Lambda SR1 Operation Manual

SR1 Audio Analyzer

Operation Manual

Stanford Research Systems

Audio

Revision 3.0.0 January, 2014

Distribution in the UK & Ireland

Lambda Photometrics Limited

Lambda House Batford Mill Harpenden Herts AL5 5BZ United Kingdom

E: info@lambdaphoto.co.uk W: www.lambdaphoto.co.uk T: +44 (0)1582 764334 F: +44 (0)1582 712084

Characterisation, Measurement & Analysis

SR1 Operation Manual2

Table of Contents

Foreword 0

Part I Getting Started

6

................................................................................................................................... 61 Unpacking and Safety

................................................................................................................................... 8

2 Manua l Revision History

................................................................................................................................... 9

3 Overview

................................................................................................................................... 13

4 User Interface

................................................................................................................................... 19

5 A Quick Example...

Part II SR1 Operation

28

................................................................................................................................... 281 File Menu

.......................................................................................................................................................... 29Save SR1 Configuration

.......................................................................................................................................................... 30

Save Partial Configuration

.......................................................................................................................................................... 31

Load Configuration

.......................................................................................................................................................... 32

Print SR1 Scre en

.......................................................................................................................................................... 33

Print Setup

................................................................................................................................... 342 Edit Menu

................................................................................................................................... 35

3 Panels Menu

.......................................................................................................................................................... 36Analog Gene rator Panel

......................................................................................................................................................... 41

Analog Generator Units

......................................................................................................................................................... 43

Analog Generator Wav eforms

.......................................................................................................................................................... 57

Digital Ge nerator Panel

......................................................................................................................................................... 60

Digital Gener ator Units

......................................................................................................................................................... 62

Digital Gener ator Wavef orms

.......................................................................................................................................................... 76

Analog Inputs Panel

.......................................................................................................................................................... 79

Digital I/O Panel

.......................................................................................................................................................... 87

Channel Status Panel

.......................................................................................................................................................... 90

Use r Status Pane l

.......................................................................................................................................................... 91

Sw e ep Pane l

.......................................................................................................................................................... 98

Settling Panel

.......................................................................................................................................................... 100

Monitors Pane l

.......................................................................................................................................................... 102

Multitone Pane l

.......................................................................................................................................................... 105

Clock Reference Panel

................................................................................................................................... 1074 Analyzers Menu

.......................................................................................................................................................... 108Com m on An alyze r Features

......................................................................................................................................................... 110

Analyzer Units

.......................................................................................................................................................... 115

Time Domain Detector

.......................................................................................................................................................... 127

FFT (Single Channel)

.......................................................................................................................................................... 141

FFT (Dual Channel)

.......................................................................................................................................................... 157

THD Analyze r

.......................................................................................................................................................... 161

IMD Analyze r

.......................................................................................................................................................... 165

Multitone Analyz er

.......................................................................................................................................................... 171

Histogram Analyzer

.......................................................................................................................................................... 175

Octave Analyze r

.......................................................................................................................................................... 177

Jitte r Analyze r

.......................................................................................................................................................... 183

Dig it iz e r

3Contents

................................................................................................................................... 1915 Displays Menu

.......................................................................................................................................................... 192Graph

......................................................................................................................................................... 199

Trace Calculator

.......................................................................................................................................................... 202

Bar Ch ar t

.......................................................................................................................................................... 205

Dig itiz e r Di s p la y

.......................................................................................................................................................... 212

Other Dis play M enu Options

................................................................................................................................... 2136 Tools Menu

.......................................................................................................................................................... 214Preferences Panel

.......................................................................................................................................................... 220

Eve nts Panel

.......................................................................................................................................................... 226

Switcher Configuration Panel

.......................................................................................................................................................... 230

Hardware Status

.......................................................................................................................................................... 231

Ne tworking

......................................................................................................................................................... 231

Network Setup

......................................................................................................................................................... 232

Netw ork Places

......................................................................................................................................................... 233

Map Netw ork Drive

......................................................................................................................................................... 233

Remo ve Ne tw o rk Driv e

......................................................................................................................................................... 234

Share SR1

.......................................................................................................................................................... 236

Compute r Functions

......................................................................................................................................................... 236

Pr inters Panel

......................................................................................................................................................... 237

Eje ct Dr iv e

......................................................................................................................................................... 237

Pow er Options

......................................................................................................................................................... 238

Date Time

......................................................................................................................................................... 238

Virtual Keyboard

......................................................................................................................................................... 238

Updating SR1

................................................................................................................................... 2417 Automation Menu

.......................................................................................................................................................... 242Remote Inte rface Panel

.......................................................................................................................................................... 243

Scripting Window

.......................................................................................................................................................... 252

Learning Mode

................................................................................................................................... 2538 Quick Measurement Menu

.......................................................................................................................................................... 254Setup Panel

.......................................................................................................................................................... 255

SNR Pan e l

.......................................................................................................................................................... 257

Re ference Panel

.......................................................................................................................................................... 259

Level Panel

.......................................................................................................................................................... 261

THD+N Pa ne l

.......................................................................................................................................................... 263

Frequency Res ponse Panel

.......................................................................................................................................................... 265

Distortion Pane l

.......................................................................................................................................................... 267

IMD Panel

.......................................................................................................................................................... 269

Crosstalk Panel

.......................................................................................................................................................... 271

Interchannel Phase Panel

.......................................................................................................................................................... 273

In/Out Phas e

.......................................................................................................................................................... 275

Automated Measurements and Reports

................................................................................................................................... 2789 Setups Me nu

.......................................................................................................................................................... 279Analog-Analog

.......................................................................................................................................................... 281

Analog-Digital

.......................................................................................................................................................... 283

Digital-Analog

.......................................................................................................................................................... 285

Dig it al -Di gi ta l

.......................................................................................................................................................... 287

Digital IO

................................................................................................................................... 28810 Help Menu

Part III SR1 Reference

291

................................................................................................................................... 2911 Front Panel Description

SR1 Operation Manual4

................................................................................................................................... 2932 Rear Panel Descritpion

................................................................................................................................... 296

3 Specifications

................................................................................................................................... 305

4 Filter Reference

................................................................................................................................... 306

5 File Reference

................................................................................................................................... 310

6 Hardw are Reference

Index 312

Part

I

Getting Started

Audio

SR1 Operation Manual6

1 Getting Started

1.1 Unpacking and Safety

Removing the Instrument From Its Shipping Container

Use care in removing the instrument from its shipping container. The SR1 weighs approximat ely 50 lbs, and can be awkward to handle while being removed from the box. In partic ular, please tak e care that the front panel LCD sc reen is not damaged while unpac king. Retain the original packing materials in case the unit ever needs to be returned for service.

Connecting The Power Cord

Your SR1 was shipped with a power cord appropriate to your location. SR1 operates from a 100V, 120V, 220V or 240V nominal AC power source with a line frequency of 50 or 60 Hz. Before connecting the power cord to the rear panel power entry module, please ensure the the LINE VOLTAGE SELECTOR card, located in the rear panel fuse holder, is set so that the correct AC input voltage value is vis ible. The fuse rating should also be checked t o see if it matches the line voltage setting. For 100V/120V operation a 4A fuse is used. For 220V/240V a 2A should be installed. The instrument has a 3-wire power cord. Be sure to connect it to a properly grounded outlet t o guard against elect rical shock.

After connecting the power cord to an AC power source, the unit can be turned on by pressing the power button at the lower left of the front panel. The green power LED above the power button illuminates to indicate the unit is on. After turning the power on the unit will take about 50 seconds to run through its boot-up sequence before it is ready for use.

Safety

Dangerous voltages, capable of causing injury or death, are present in this inst rument. Use extreme caution whenever the instrument cover is removed. Do not remove the instrument's cover while the power cord is connected to a live outlet. Do not expose the instrument to rain or exc essive moisture. Do not attempt to disconnect the internal cooling fans or block the fan vents.

Service

Refer all servicing to qualified, SRS-authorized service personnel. Do not attempt to substitute parts or perform any unauthorized modification to the instrument. Contact SRS for inst ructions on how to return the ins trument for authorized service, calibration, or adjus tment.

Stanford Research Systems 1290-D Rea mw ood Ave. Sunnyvale, CA, 94089 USA

p

hone 408.744.9040

email info

@

thinksrs.com

web www.thinksrs.com

Getting Started 7

SR1 Operation Manual8

1.2 Manual Revision History

No part of this manual may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or by any information storage and retrieval system without permission in writing from Stanford Research Syst ems, Inc.

Manua l Revision History

Version Date Author Comments

1.0 1/06 jahan Original Version

2.0 7/09 ajm Preliminary Version shipped with first SR1s

2.1 10/09 ajm 2nd Preliminary version

2.2 12/09 ajm Complete Through Tools Menu

2.3 1/10 ajm Complete Manual

2.4 3/10 ajm For SR1 v 1.1

2.5 3/10 ajm Minor Printing Corrections

2.6 5/10 ajm Updated for SR1 v1.1.6

2.7 7/10 ajm Updated for SR1 v1.2

2.8 6/11 ajm Updated for SR1 v1.4

3.0 1/14 ajm Updated for SR1 v2.1.13

Copyright and Trademark Acknowledgements

Windows is a trademark of the Microsoft Corporation

Apache Xerces

This product includes software developed at The Apache Software Foundation (http:/ /www.apache.org/).

Portions of this software were originally based on the following:

NI-De vice

FastReport

Getting Started 9

1.3 Overview

SR1 is versatile and complex instrument capable of making a wide a variety of precision audio measurements in both the analog and digital domains. The following is a brief introduct ion to t he different pieces of SR1 and their capabilities.

Measurement Setups

SR1 includes pre-configured setups for many common audio measurements. To get up and running quickly, see the Setups Menu

.

Generators

SR1 contains precise and flexible analog and digital audio generators. Eac h generator is built around several core waveforms which can be either generated individually or combined in the generator and output as a composit e signal. For the Analog Generator, the core waveforms include Sine, Low-Disortion Sine, Phased Sine, Noise, USASI Noise, Squarewave, Ramp (triangle), FFT Chirp, Multitone, Arbit rary, and Constant (offset). The analog generator can be output either as a balanced or unbalanced signal and ouputs a maximum peak output voltage of 20 V (unbalanc ed) or 40 V (balanced).

The Digital Generator offers the same core waveforms as the analog generator and additionally offers a number of waveforms optimized for digital interface test ing including Digit al Constant, Digital Counter, Walking Bits, and a J-test waveform designed to test the jitter susc eptibility of devices.

Analog Inputs

SR1 offers both balanced and unbalanced analog inputs with full scale input ranges from 160 Vrms down to 62 mVrms. SR1's analog inputs are autoranging, meaning that for most input signals, the analyzer automatically s ets the input range without any user interaction.

Digital Audio Inputs and Outputs

SR1 has 2 sets of XLR and BNC connectors and is c ompatible with both consumer and professional digital audio signals from 50 mVpp up to 10.2 Vpp. All significant parameters of the digital audio carrier signal are measured including s ignal amplitude, digital audio effective sampling frequency, and input/ output delay. Status bit s are fully decoded in both the the professional and consumer standards. User bits are also display ed in raw binary format.

Several impairment signals can be applied to the output digital audio carrier inc luding Common Mode Sinewave, Normal Mode Noise, and Jit ter. Jitter waveforms include Sine, Square, Noise, and Bandpass Noise with a peak jitter amplitude of ~13UI.

Analyzers

There are 8 different types of Analyzers in SR1, s ummarized below.

Time Domain Detector Makes wideband amplitude, ratio, and THD+N measurements. The time

domain detector signal chain includes bandpass or notch filters, bandwidt h limiting filters, and a variety of different weighting filters. Peak , RMS and Quasi-Peak responses are selectable

FFT (1 ch) Provides single-channel FFT functionality.Measurements inc lude power

spectrum, time record, phase. Both zoom (changing the FFT frequency range) and heterodyne (moving t he FFT frequency range) are included.

FFT (2 ch) Provides dual-channel FFT functionality.Meas urements include power

spectrum and time record for both channels, plus frequency response

SR1 Operation Manual10

(transfer func tion), and interchannel phase. Zoom (changing the FFT frequency range) is supported in the dual-channel analy zer.

THD Ana lyze r Makes frequency selective Total Harmonic Distortion (THD) measurements,

both ratio and absolut e. Includes the ability to measure only selected harmonics.

IMD Analyzer Makes st andard Intermodulation Distortion measurements including

SMPTE/DIN, CCIF (difference frequency), and DIM/TIM.

Multitone Analyzer Makes single-shot multitone measurements allowing fast measurements of

common audio parameters including noise, distortion, and level.

Jitter Analyze r Measures the jitter of the digital audio c arrier in both the time and frequency

domain including variable high and low pass filtering.

Histogram Analyzer Creates histograms of the analog and digital audio input s ignals.

Octave Analyzer Displays 1, 1/3, and 1/12 fractional octave spectra.

Each type of analyzer has a c orresponding panel with the appropriate controls for that analyz er and readouts for the analyz er's measurements. At any instant, there are two active analy zers, designated A0 and A1. The user can select the ty pe of A0 and A1 from any of the allowed analyzer types. Each analyzer has c ontrols which set the input domain to analog or digital audio and s elect the appropriate input c hannel.

For analog inputs SR1 offers an additional choice between two Analog-to-Digital c onverters, each optimized for different meas urements . The high-bandwidth (Hi BW) 16-bit ADC operates at a fixed sampling rate of 512 kHz. The high-resolution (Hi Res) ADC is a 24-bit converter which operates at fix ed sampling rates of 128 kHz and 64 kHz and and variable rates which can be sync hronized with the digital audio output or input s ignal to perform cross-domain measurements.

Sweeps and Free Run

SR1 operates in two different measurement modes: free-run and sweep. In free-run mode the analyzers make continuous measurements and continually updates the measurement results on the analyzer panels.The second mode, sweep mode, requires that several options be s et. First , a sweep source must be configured which determines whether SR1 will be sweeping an internal parameter (e.g. generator frequency) over a specified range, an externally measured parameter (e.g. input frequency), or at regular time intervals. Once the s weep source is configured the user must s elect the measurements (up to 6) that will be recorded during the sweep. Swept measurements mus t be settled to be included in the sweep meaning that t he transient variability of the measurement must drop below a user set value before being included in the sweep result. Sweep sources and data are setup on the Sweep Panel

, while

Settling parameters are set in the Settling

panel.

Displays

Three different types of displays are available for graphically displaying measurement data. The graph is the main display ty pe and is capable of displaying many different live and off-line data t races both. Graphs include cursors for reading out absolute and delta values, the ability to export to bitmap and Windows Metafiles, movable onscreen annotations, and a variety of data calculations (smoothing, linearit y, maximum and minimum, etc.) for manipulating data. The Bar Chart

is a simpler display optimized for displaying a single measurement value which reports the instantaneous value of the measurement as well as maximum, minimum, and standard deviation. The Digit izer Display

is designed to work with the optional digitizer and displays various meas urements calculated by the digitiz er including full-color eye diagrams.

Getting Started 11

Digitizer (Optional)

The optional digitizer digitizes the digital audio carrier signal at an 80 MHz s ampling rate. The digitizer calculates the overall clock rate of the signal as well as jitter as a function of time and probability density for pulse width, pulse amplitude, input amplitude, and jitter amplitude. The digitizer als o calculates the s pectra of both the carrier signal as well as the jitter signal. Finally the digitizer calculates an eye diagram which shows the probability of the carrier signal as a function of amplitude and time. The off-line measurements made by the digitizer complement the real-time jitter measurement capabilities of the Jitter Analyzer.

Remote Interfacing

SR1 Supports a variety of remote interfaces:

IEEE-488.2 (GPIB)

SR1 has a rear-panel IEEE-488 connector and fully supports the IEEE-488.2 standard. All instrument features c an be set and queried from the remote interface.

Serial

GPIB c ommands may also be sent over the rear-panel serial connec tor which supports baud rates up to

115.2 kBaud.

TCP/IP

GPIB c ommands may also be sent over a TCP/IP network via the rear-panel ethernet connector. SR1 follows the VXI-11 standard for the transmission of commands over TCP/IP.

COM

SR1 is fully COM enabled allowing applications such as Visual Basic to set and query instrument internals. COM enabled applications may also control and query the instrument remotely over ethernet. Not that firewall settings may need to changed to fully enable this functionality .

SR1 Operation Manual12

Getting Started 13

1.4 User Interface

The SR1 audio analyzer user interface is based on software that runs on the Microsoft Windows operating system. As such, the basic user interface, based on standard Windows menus and controls, should be familiar to most users who have used Microsoft Windows. The s ame software that runs on the instrument is available for free download from Stanford Research Syst ems (www.thinksrs.com

) and can be run on any W indows PC. While no measurements can be made while running on a PC, this mode is perfect for offline viewing of saved datafiles or simply becoming familiar with the software.

Like all Windows software, operating SR1 requires a point ing device and a means of entering text and numeric data. The instrument provides several options depending on the intended environment.

External Mouse and Keyboard Control

SR1 can be used with an external mouse and keyboard. The mouse and keyboard must be connect ed to the rear-panel connectors before the instrument is turned on to be properly recognized by the instrument. Operation with an external mouse and keyboard is convenient when SR1 will be used in a benchtop environment.

Using the Trackpad

For situations where it's inconvenient to use an external mouse (e.g. rac kmount), SR1 has a front-panel trackpad which can be used as a pointing device. (Note that the trackpad is always active, even when an external mouse is connected.) To use the trackpad, drag your finger over the surface of the pad to move the cursor on the s creen. To "left-click" gently tap your finger. To "double-click" tap your finger twice. Finally, to "right-click" tap your finger in the upper-right triangle (colored in a light er shade of gray).

Using the Front-Panel Keypad

The front-panel keypad provides a convenient way to enter numeric values as well to access some commonly used SR1 functions without having to reach for the mous e or keyboard.

SR1 Operation Manual14

Standard Function of Keypad Keys

Key Function

Nume ric Entry Ke ys

Numbers 0-9 Enters the c orresponding digit at the current cursor position.

. (Decimal Point) Enters the decimal point at the c urrent cursor position.

± Changes the sign of the number in the current entry field.

Backspace. Deletes the character to the left of the cursor.

Exp Inserts the "E" character at the current cursor position allowing entry in

scientific notation: e.g. 1.2E3

Esc Aborts numeric entry and returns the value in the selected field to the

previous value.

micro

inserts the "u" modifier at the cursor position, interpreted as x10-6.

milli

inserts the "m" modifier at the cursor position, interpreted as x10-3.

kilo

inserts the "k" modifier at the curs or posit ion, interpreted as x103.

Mega

inserts the "M" modifier at the cursor position, interpreted as x106.

Enter Finishes entering the new value.

Function Keys

Page Rotates through the seven pages of the page control on the SR1 screen.

(Tab Left /Right)

Moves the control with "focus" either to the next or previous control.

Sweep

Starts a Sweep. Equivalent to press ing the button on the speedbar.

Pause Pauses and resumes both sweeps and free-run mode. Equivalent to pressing

the

and but tons on the speedbar.

Run

Starts free-run mode. Equivalent to pressing on the speedbar.

Translate graph left/right. Once pressed, the keys will move the data in t he current graph left and right. Press "Esc" to exit this mode.

Zoom X-axis. Once press ed the keys will zoom the X-axis in and out. Press "Esc" to exit this mode.

AutoScale. Autoscales the X and Y ax es of the c urrently selected graph.

Max Moves the active cursor in the current graph to the position corresponding to

the maximum value displayed in the graph.

Cursor If the selec ted graph cursor is off, this key turns cursors on. If they are on,

this key toggles the active cursor between the two cursors.

Alt Selec ts the Alt function (written in Green above the keys) for the keypad

keys.

Alt-Function Keys

Menu Moves focus to the main menu. Once Menu is pressed, the knob and enter

keys can be used to acces s the main menu s elections without us ing a pointing devic e.

Sticky Normally, the knob varies whatever control on the screen currently has focus.

Press Sticky to "Stick" the knob to the current control. Even when focus is moved to a different control the knob continues to modify the sticky control. The sticky control is drawn with a

yellow background. Press sticky again to

Getting Started 15

exit sticky mode.

Local Upon receipt of a command from one of the remote interfaces SR1 is placed

in "Remote" mode. Using this key returns the unit to local c ontrol.

Ref AutoReference. The contents of the currently focused control is examined. If

it is a frequency, the frequency is moved to the frequency reference of the selected analyzer. The analyzer, A0 or A1 is selected by press ing the

keys after pressing "Ref". If the contents of the currently focus ed window is not a frequency then the contents of the A and B levels for the selected analyzer will be transferred to the dBrA and dBrB references (either analog or digit al, depending on the analyzer input.)

Hex, Hex Digits A-F

Hex Entry mode. Places a "0x" charact er in the c urrently focused c ontrol to begin hexadecimal entry. In this mode, the "A", "B", "C","D","E", and "F" characters above the micro, milli, kilo, meta, Exp, and Page keys are act ive allowing the entry of a hexadecimal value. Hex Entry mode is terminated when "Enter" is pressed.

Generator

After pressing this key press to open the analog generator panel or

to open the digital generator panel.

Analy zer

After pressing Analyzer press to open t he A0 panel or to open the A1 panel.

Alpha Calls up the virtual keyboard.

Translate graph up-down. Once press ed, the keys will move the data in t he current graph up and down. Press "Esc" to exit this mode.

Zoom Y-axis. Once pressed the keys will zoom the Y-axis in and out. Press "Esc" to exit this mode.

Autoscale X, Y

After pressing the key, use t he keys to select autoscale of either the the X or Y axis.

Min Moves the active cursor in the current graph to the position c orresponding to

the minimum displayed value in the graph.

Help Brings up the online help.

Using the Knob

Turning the knob modifies the currently focused control. If the control is a unit entry control, the knob increments and decrements its value with an appropriate resolution. If the control is a drop-down list the knob cycles through the entries in the list. Three different knob acceleration profiles c an be selected from the preferences panel

. A control can be selected as "Sticky" in which case the knob will continue to control it even though focus is given to another control. When cursors on a graph are active the knob controls the active cursor position.

Using the Virtual Keyboard

For situations where it's necessary to enter text into a cont rol and an ext ernal key board is not available the Virtual Keyboard can be selected from the SR1 keypad

or from the Tools Menu. The virtual keyboard offers the full functionality of a standard PC keyboard but c an be operated with just a mouse or the trackpad.

SR1 Operation Manual16

Keyboard Shortcuts

A number of keyboard shortcuts are available (us ing either an external keyboard or the virtual key board) to simplify the execution of common functions.

Key Sequence Action

<Ctrl> 1-7 Selec t the designated page (1-7) on the page control as the active page.

<Ctrl> D Opens the digital generator panel.

<Ctrl> G Opens the analog generator panel.

<Ctrl> I Opens the digital i/o panel.

<Ctrl> A Opens the analog inputs panel.

<Ctrl> M Opens the monitors panel.

<Ctrl> W Opens t he sweep controller panel.

<Ctrl> T Opens the scripting window.

<Ctrl> [ Opens the A0 analyzer panel.

<Ctrl> ] Opens the A1 analyzer panel.

F4 Auto-reference analyz er A0. Moves the current A0 level A and B values to the dBrA

and dBrB reference values.

<Ctrl> F4 Auto-referenc e analyzer A1.Moves the current A1 level A and B values to the dBrA

and dBrB reference values.

F12 Emergenc y shutoff. Turns off all channels of the analog and digital generators.

<Ctrl> F12 Restore generators. Turns on generator channels that were turned off with F12.

Scripting Window Shortcuts

<Ctrl> S Save the current script.

<Ctrl> O Open a script.

<Ctrl> N Create a new script.

<Ctrl> C Copy selected text to the clipboard.

<Ctrl> X Cut selected tex t and copy to the clipboard.

<Ctrl> V Paste clipboard text at the cursor location.

<Ctrl> F Brings up the dialog for finding text in the script.

<Ctrl> R Brings up the dialog for finding and replacing text in the s cript.

<Ctrl> P Prints the current script.

Getting Started 17

Unit Entries

The Unit Entry is a type of control used extensively throughout SR1 that allows entry of numeric data in a range of different unit s. The example below shows the generator amplitude control for example. W hen

the down-arrow

is clic ked, a the current value of the

entry is shown in the drop-down lis t expressed in each of the allowed units. Selecting a different unit makes it the current unit for subs equent entries. To enter a new value into a unit entry first click anywhere on the current text, and then enter a new numeric value followed by an optional modifier character. The allowed modifiers are:

Character Modifier Numeric Value

f femto

x10

-15

p pico

x10

-12

n nano

x10

-9

u micro

x10

-6

m milli

x10

-3

k kilo

x10

3

M mega

x10

6

G giga

x10

9

T tera

x10

12

(Note that the front-panel k eypad contains dedicated keys for the unit-modifiers just to the right of the Enter key.) To complete the entry press the "Enter" k ey on the front panel or an external keyboard. To abort the entry press the "Esc" key on t he keypad or keyboard.

Somet imes the precision of the value represented by a unit entry may exceed the number of digits displayed. To s ee the value of any unit entry displayed with full double precision hold the cursor over the unit ent ry— the full double precision value will be shown as a "hint."

Unit Displays

Unit Displays are the controls with a black bac kground and green text which are used to display measurement results and other quantit ies whose value can't be changed by the user. As with unit

entries , the units of the unit display can be changed by using the mouse or trackpad to click on the at the right of the control and select a unit from the drop-down list. Right-clic king the Unit Display brings up a menu which offers some more options:

SR1 Operation Manual18

Normally the Unit Display auto-selects the appropriate unit-modifier for the currently displayed value. For instance 1.2x10

-6

Vrms would be displayed as 1.2 Vrms. There are situations where it might be

desirable to lock the unit-modifier selection. For instance we might want the display to readout as

0.0012 mVrms. To do this, select the appropriate modifier from the right-click menu. Select "Aut o" from the right-click menu to return to normal operation.

The second feature offered by Unit Displays is selected in the bottom half of the right-click menu. In "Standard" mode, the Unit Display displays each new value that is sent to it . If one of the other modes are selec ted, the current value of the display is saved as the "reference" and subsequent updates are displayed as follows:

Mode Operation

Standard Each update to the Unit Display's value is displayed.Data is displayed in Green.

Max Updates are display ed only if they are greater than the reference value. When the

data exceeds the reference that data becomes the new reference value. Data is displayed in Re d.

Min Updates are display ed only if they are less than the reference value. When the

data is less than the reference that data becomes the new referenc e. Data is displayed in Bl ue .

Delta The difference between the update value and the reference value is displayed.

Data is displayed in Purple.

To reset the reference double-click the display .

Like unit entries, it is possible to s ee the value represented by a unit display with full double precision by holding the cursor over the unit display— the double precision value will be shown as a "hint."

Getting Started 19

1.5 A Quick Example...

In this example we'll use the analog generator to c reate a signal with a known amount of distortion and we'll use the Time Domain Detector to measure the distortion and the FFT analyzer to look at the distortion in the frequency domain. To begin, turn on SR1 and wait for the instrument to finish its s tartup sequence. No external cables will be necessary for this demo. Feel free to use the front panel trackpad and keypad keys to control the instrument, or if you've got an external mouse and key board you can those. We won't go into ex cruciating detail on how to select items and use the controls because they're standard Windows controls and their operation should be familiar.

Start out by using the speedbar at the top of the SR1 screen to open the Analog Inputs panel and the Analog Generator panel, and from the Analyzers menu, set Analyzer 0 to Time Domain Detec tor. Thes e three panels may automatically open when SR1 is powered up.

SR1 Spe edbar

Note that the icons for the Analog Inputs panels and the Analog Generator panel are both orange . SR1 uses orange to denote items associated with the analog domain and blue to denote items ass ociated with the digital audio domain. Most panels have color bars under the title of the panel indicating the domain associated with the panel.

The three panels y ou've jus t opened should look like this:

Now let's configure the instrument for this example. On the Analog Inputs panel, change the Input Source for both channels from BNC to GenMon. With the inputs set to GenMon the Ch. A analog input is directly connected t o the Ch. A generator output and the Ch. B analog input is directly connec ted to the Ch. B generator output. Leave the "Auto" box checked for each of the range c ontrols. With Auto Range on, SR1 automatically adjusts the range to the optimum value for the c urrent input signal. Note that the ranges are set to their minimum value (62.5 mVrms) and the Input Level indicators are showing blue (below half scale). That's because the generator hasn't been set up yet.

SR1 Operation Manual20

Take a look at the Analog Generator panel. We haven't selec ted any waveforms yet, so the tab cont rol at the bottom only contains the configuration tab. By default, the generator is in "Mono" mode which means that the same waveform will be output on the A and B channels . W e can adjust the channel amplitudes s eparately, but the waveform is the s ame. (In "Stereo" mode we can select different waveforms for A and B but we don't need to do that for this example.) Now press the "New" button on the Analog Generator panel. This brings up the menu of available waveforms. From the Sine submenu choose "Normal Sine". After the Sine waveform shows up in the tab control set an amplitude of 1Vrms. Note how the range c ontrols on the Analog Input panel both move to the 1 Vrms input range and the Input Level indicators turn green, indicating the ranges are optimally adjus ted. (The Input Level indicators are also visible at the bottom right of the SR1 screen.) Now we can add a little bit of distortion to t he signal. Pres s the "New" button again on the Analog Generator panel and once again select a "Normal Sine". This time set the frequency to 2 k Hz and the amplitude to 1 mVrms. We've just illustrated a key feature of the SR1 generator's architecture— the ability to combine several waveforms in the generator. The 1 kHz 1 Vrms signal and the 2 k Hz 1 mVrms signals are added in the generator. Using this technique an almos t infinite variety of waveforms c an be created in the generator to suit almost any test situation.

Now let's measure the properties of the signals just created. Look at the Time Domain Detector panel and change the source from Digital A to Analog A. The "Converter" field will read "HiRes" indicating that the analy zer is using SR1's 24-bit High-Resolution converter. The current s ampling rate for this converter, 64 kHz, is displayed in the "Fs" field next to the converter selection. SR1 uses two high quality analogto-digital converters (ADCs) for analysis of analog signals— a 24bit high-resolution converter that can operate over a variety of sampling rates and a 16 bit high-bandwidth converter that operates at a fixed sampling rate of 512 kHz giving the instrument an analog bandwidth of 200 kHz. The differences between the two converters will be discussed in detail later but for now we can leave the converter selection at "HiRes."

Press the

button at the top left of the screen to start the measurements. Note that the Status Indicator at the bottom left of the screen. SR1 operates in two distinct measurement modes. In "Free Run" mode, which we jus t started, all the analyzers make continuous measurements and cont inuously update the results on the analyzer panels and displays . This mode is us eful for benchtop ex ploration like we're doing now. "Sweep" mode is a more structured measurement mode in which the instrument sweeps a certain parameter and only measures data at certain defined values of that parameter. Sweep mode is more useful for repetitive testing to standards. We'll do a sweep at the end of this demo as an example. For now observe how in Free-Run mode the analyz er's level and amplit ude displays are continuously updated.

To measure the " distorted" sine signal we've c reated, select "THD+N Ratio" as the Measurement in the Time Domain Detector. Change the units of the Amplitude display to dB, and the three panels should appear as they do below:

Getting Started 21

When " THD+N" ratio is selected, the analyzer inserts a deep notch filter at the frequency of the fundamental. In this case, becaus e the notch filter is set to be tuned to the measured frequency, it is s et at the 1 kHz dominant frequency of our generator signal. The Time Domain detect or then performs an RMS integration of the remaining signal, which is distortion plus noise, and displays the ratio of that signal to the total amplitude of the input Note that the measured THD+N ratio is -60 dB. (1 mV / 1 V = 60 dB).

To show how much more SR1 brings to a standard distortion meas urement s elect the second analy zer (A1) as the FFT1 analyzer. W hen the panel is displayed, change the source of the Analyzer to "Other Analy zer". In this mode the FFT analyzer and the Time Domain Analyzer work as a team; the FFT analyzer looking at the notch filtered signal from the Time Domain Detector. Take a look at the information displayed on the FFT1 analyzer panel:

Like all analyzers t he input s ource is displayed at the upper left. The analyzer sampling rate is displayed at the upper right. Because we've connec ted the FFT analyzer to the output of the Time Domain Detector

SR1 Operation Manual22

the sampling rate for the FFT analyzer is also 64 kHz. Just underneath is the control for setting the number of FFT lines (resolution). The resolution can be set to values between 256 lines and 32k lines. Unlike most Audio Analyzers, SR1's FFT analyzer doesn't operate at a fixed frequency range from DC to Fs/2. The Bandwidth control allows s etting the meas urement range to Fs/2, Fs/4, etc., all the way down to Fs /2048. The full FFT resolution is applied to this narrower frequency range, which can be moved to any position in the range of DC to Fs/2 using the "S tart," "Center," and "End" controls. We will illustrate this shortly.

Averaging can be applied t o the FFT t o lower the shot-to-shot variation in the noise, or in some cases to actually lower the amount of noise. Select 5 averages in the "# Avgs" field to create a nice stable FFT display.

To display the FFT results we'll need to create a graph. Click on "Page 2" of the page control to give us

some room for the graph and click on the

icon to create a new graph. Maximize the graph with the standard maximize c ontrol in the upper right. Now we need to add some data to the graph. Clic k the "Plus" sign icon at the top left of the graph to add a trace to the graph. The "Add Trace" menu appears. Open the "A1 FFT" node to see the measurements produced by the A1 FFT analyz er.

Note that scalar measurements, like frequency or level, are denoted with the icon while vector

measurements like s pectra are accompanied by the

icon. Selec t "Power Spectrum", click ok, and the FFT will appear. Since we're looking at a very wide dynamic range, some logarithmic units will help. Click on the "Ymax " Unit Entry and change the Y units to " dBVrms". Now click the "Log" box in the X axis row to select a logarithmic X-axis. Click on the

icon (autoscale) on the graph speedbar to

autoscale the display. Now turn on the graph cursors by clic king the

icon. Use the knob or the

mouse to drag cursors as shown below. The graph should look like this:

Getting Started 23

Now we're ready to zoom in on a portion of the the distortion product s pectrum. Go back to Page 1 of the page control, and in the bandwidth control of the FFT analyz er selec t 500 Hz.In the "Center Frequency " field s elect 1 kHz. We're narrowing the bandwidth by a factor of 64, still using 1k FFT lines, and centering the new bandwidth on the notc hed out fundamental. Go back to Page 2, autoscale the spectrum, which should now look like this:

SR1 Operation Manual24

Note how more detail is resolved inside the notch. Go back to the FFT analyzer on page 1 and press the "Baseband" button to return the analy zer to it's full measurment range. We're now ready for the las t step in the demonstration.

Setting Up a Sweep

On page 1 click on the icon to open the sweep controller panel.W e're going to sweep the amplitude of our "distortion" sine wave and record the measured THD+N from the Time Domain Detector: Clic k on the Sweep Source button to bring up the sweep source selection menu:

SR1 has 3 main ty pes of sweep sources: Time Sweeps, where the s weep occurs at fix ed time intervals, Internal Sweeps, where the s weep occurs at fixed values of some internal parameter, and External Sweeps, where the sweep occurs at fixed values of some externally measured parameter. Since we're going to s weeping the amplitude of the sinewave we created in the generator, this will be an "Internal" sweep. Open the Internal node on the tree, and then open the AnlgGen (Analog Generator) node to show the associated parameters that can be swept. Note that there are two sine amplitudes and frequencies shown, Sine(0) and Sine(1). That's because we created two sinewaves in the generator. The first, Sine (0), refers to the 1 kHz fundamental. The second, Sine(1) is the "distortion" s inewave whose amplitude we're going to sweep. Double-click on ChA:Sine(1):Amp to select it and return to the sweep panel:

Getting Started 25

Selec t the start amplit ude as 100 uVrms and the stop amplitude as 100 mVrms. Leave the number of sweep steps at 30, but select "Log Step Size." Next we need to select that data that will be measured in the s weep. Up to 6 separate measurements can be recorded at each sweep point. Click on the Sweep Data "()..." to specify the sweep data. From the Sweep Data Selection menu, open the A0 node since the measurement we're going to record, THD+N, is made by the currently active Time Domain Detector on A0:

SR1 Operation Manual26

Selec t Analog THD Ratio A by double-clicking it. We're now ready to set up the graph to display our sweep.

Return to Page 2 of the page control. In the t race listing panel at the bottom of the graph unclick the Power Spec trum trace that we were looking at previously. Now use the "Plus" button at the top of the display to add another trace to graph. This time open the "Sweep" node and selec t "THD Ratio A". Selec t a log X-axis (to match the log sweep we just specified, and s elect dB as the Y-axis units with the unit ent ry controls. Select a Y axis range from -95 to -10 dB. Now start the sweep by pressing the "Sweep" button on the front panel. After a few seconds you'll see the results of the sweep:

This, of course, is exactly what we expect. At an amplitude of 100 uVrms, the THD+N is simply 20*log (100 uV/1V) = -80 dB. At the other of the s weep the the THD+N is 20*log( .1V / 1V) = -20 dB.

This quick example only scratches the surface of SR1's capabilities, but should give you a feeling for how the ins trument operates.

Part

II

SR1 Operation

Audio

SR1 Operation Manual28

2 SR1 Operation

2.1 File Menu

The File Menu contains options for saving and recalling instrument configurations and also for printing.

Save SR1 Configuration

Saves the entire inst rument s etup to a configuration file.

Save Partial Configuration

Saves the entire inst rument s etup to a configuration file.

Load Configuration Loads set up information from a configuration file.

Print SR1 Screen Prints the currently displayed screen to the currently selected printer.

Print Setup Displays the standard Windows Print Setup dialog allowing the selec tion of

an installed printer and paper options.

SR1 Operation 29

2.1.1 Save SR1 Configuration

Selecting File Save SR1 Configuration saves the entire instrument setup to an SR1 configuration file. Configuration files are XML files whose structure is detailed in the SR1 File Reference

. The default extension for configuration files is ".XML".All operating parameters, as well as the the pos ition of all panels and display s are recorded in the configuration file. After loading the file the instrument state will be exactly what it was when saved.

The trace data option governs how SR1 will save data stored in graphs. "Never Save" means that no graph data will be saved along with the configuration file. The file, in t his case, is a pure "settings" file. "Always Save" means that all graph data, including live measurements, will be saved with the configuration file. "Save if Offline" means that only offline graph data, such as reference curves or limits, will be saved with the configuration.

SR1 Operation Manual30

2.1.2 Save Partial Configuration

Selecting File Save Partial Configuration allows a choice of which portions of the ins trument setup will be saved to the SR1 configuration file. After selecting this option, the Save Partial Configuration dialog box is diplayed.

Selec t the portions of the instrument configuration to save and click "OK" to display the s tandard SR1 file save dialog box .

SR1 Operation 31

2.1.3 Load Configuration

File Load Configuration loads the instrument's configuration based on the values found in the file

selected with the standard Windows file open dialog box. After selecting the file, a dialog is displayed allowing s election of individual configuration areas. The default is to load all the configuration information in the file. Only configuration areas found in the s elected file have a clickable checkbox, the rest are grayed out.

Selec t the portions of the instrument configuration to load and click "OK" .

SR1 Operation Manual32

2.1.4 Print SR1 Screen

File Print SR1 Screen prints the full main window of the program, including menus and borders, to the current printer. Printer and paper options are selected from the File

Print Setup dialog. Note that

File

Print SR1 Screen always prints the entire screen exactly as it appears. Other options are

available for more formatted printing and ex porting of data from displays

.

SR1 Operation 33

2.1.5 Print Setup

File Print Setup displays the s tandard Windows print setup dialog box.

When running the SR1 program from a W indows c omputer, use whatever printers have already been installed. When using the SR1 instrument, use the Tools

menu to connect SR1 to a network and install

and configure network printers .

SR1 Operation Manual34

2.2 Edit Menu

The Edit menu supplies the standard Windows edit ing functions: Cut, Copy, Pas te, and Delete.

Cut Deletes the c urrently selec ted text and c opies it to the clipboard.

Copy Copies the currently selected text to the clipboard without deleting it.

Paste Copies the clipboard contents to the current cursor location.

Delete Deletes the currently selected text wit hout copying it to the clipboard.

Note that in addition to being useful for transferring text, the edit commands may be used to transfer Graph Traces between different graphs

.

SR1 Operation 35

2.3 Panels Menu

The Panels menu provides access to the various panels which c ontrol the operation of the instrument. SR1 panels are fixed size windows— they're not resiz able. They can be minimiz ed, maximized, or

closed with the standard Windows tools :

.

Multiple copies of the s ame panel may be maint ained on different pages of the main display. In general, changes made to a panel on one page are automatically updated on t he other pages.

Panels are color coded according to the domain to which they apply. Panels relevant to the digital domain have a light blue bar under the title bar

.

Panels which are relevant t o the analog domain have an orange bar under the title.

Analy zer Panels, which can operate in either domain, have either the light blue or orange bar depending on whether the analyzer is operating in the digital or analog domain.

The following panel selections are available from the panels menu.

Analog Generator Panel

Controls the operation of SR1's Analog Generator.

Digital Generator Panel

Controls the operation of SR1's Digital Audio Generator.

Analog Inputs Panel Configures t he analog inputs.

Digital I/O Panel Configures the Digital Audio Carrier Input and Output configuration.

Sweep Panel Sets up one or two dimensional sweeps.

Settling Panel Configure the settling parameters for sweep measurements.

Monitors Panel Configures the source and level for the monitor outputs.

Multitone Panel Configures the analyzer and generator settings for multitone measurements.

Clock Reference Panel Locks the SR1 system clock to a variety of external sources.

SR1 Operation Manual36

2.3.1 Analog Generator Panel

The Analog Generator Panel controls the operation of SR1's analog generator. The generator can be populated with many different waveforms— sines, square waves, ramps, etc. Many of the waveforms can be combined by the generator. For instanc e, if the generator is populated with sinewave and noise, than the output will be the sum of the sinewave and noise signals. The amplitudes of each component of the composite signal are adjustable separately as is the overall amplitude of the combined signal. Some waveforms, (USASI noise, for instance) are special-purpose test signals and may not be combined with other waveforms.

The tabs corresponding to each particular waveform are described in Analog Generator Waveforms section. This sec tion des cribes the controls and settings of the analog generator that are relevant to all waveforms.

Note that the SR1 Analog Generator is completely separate and independent of the Digital Audio Generator. The t wo generators operate simultaneously and independently with different waveforms.

Output Controls

Fs c ontrols the output sampling rate and D/A converter selection for the analog generator. SR1 uses

two different types of D/A converters to generate high-quality analog waveforms, a 16-bit converter operating at a fixed output sampling rate of 512 kHz and a 24-bit converter which operates at a variety of sampling rates. Each converter has advantages depending on the specific application. See the

Specifications

section for detailed information on each of the converters.

512 kHz Selects the Hi-Bandwidth 16-bit converter operating at a fixed output rate of 512 kHz.

This setting allows a maximum waveform frequency of 200 kHz.

128 kHz Selects the Hi-Resolution 24-bit converter operating at a fix ed sample rate of 128 kHz

providing a maximum waveform frequency of 57.6 kHz

64 kHz Selects the Hi-Resolution 24-bit converter operating at a fix ed sample rate of 64 kHz

SR1 Operation 37

providing a maximum waveform frequency of 28.8 kHz

OSR Synchronizes the sampling rate of the analog generator to the digital audio output

sampling rate set in the Digital I/O

panel.This setting is useful for performing cros s-

domain measurements using the FFT Chirp waveform or Multitone

techniques.

Maximum waveform frequency is 45% of the digital audio sampling rate.

ISR Synchronizes the sampling rate of the analog generator to the sample rate of the

received Digital Audio signal. Maximum waveform frequency is 45% of the digit al audio sampling frequency.

Mode c ontrols the output mode of the Analog Generator.

Mono The same waveform is output to both the A and B channels. The amplitude of each

channel is still separately adjus table, but the waveform is the same.

Stereo Each channel can be configured with a different waveform.

Output Configuration selects the output connector configuration. (See the diagram below)

Unbal Gnd. Outputs to the both the XLR and BNC connectors . The BNC shield and XLR pin 3(-) are

connected to chass is ground through a 5

resis tor. XLR pin 1 is connected directly to chassis ground. The BNC center pin and XLR pin 2 bot h are connected to the unbalanced signal.

Unbal Floa t Outputs to the both the XLR and BNC connectors. The BNC shield and XLR pin 3(-) are

connected to chass is ground through a high impedanc e (~100k,1uF). XLR pin 1 is connected directly to chassis ground. The BNC center pin and XLR pin 2 both are connected to the unbalanced signal.

Bal Gnd. Outputs to only the XLR connectors. XLR pin 1 is connected directly to chassis ground.

XLR pins 2(+) and 3(-) c arry the balanced s ignal whic h is symmetric around chas sis ground.

Bal Floa t Outputs to only the XLR connectors. XLR pin 1 is connected directly to c hassis ground.

XLR pins 2(+) and 3(-) c arry the balanced s ignal whic h is unreferenced to chassis ground.

Bal Com mon Similar to Balanced Ground except that t he same signal is present on pins 2 and 3.

This allows testing the Common Mode Rejec tion Ratio of external devic es.

SR1 Operation Manual38

Analog Gene rator Output Connections

Output Impedance selects the Analog Generator output impedance.

SR1 Operation 39

25 , 75 , 600 Allowed impedance values for unbalanced out puts

50 , 150 , 600 Allowed impedance values for balanced outputs

Waveform Controls

The New button displays the Waveform Selection Submenu.

The selected waveform will either be added to the output for one or both channels depending on the Mode setting. Certain waveforms (for instance Low Distortion Sine) cannot be combined with other waveforms. When one of these waveforms is selected all of the current waveforms are deleted. Other waveforms simply add to the current output when selected.

The Delete button deletes the currently selected waveform.

The A/B selection buttons only appear when the generator Mode is set to Stereo. The buttons determine which channel a newly added waveform will appear on. When the mode is c hanged to stereo, any waveforms present will be assigned to channel A. When the mode is changed from stereo to mono, all channel B waveforms are deleted and the channel A waveforms are output on both channels.

Amplitude Controls

The Channel Gain control varies modifies the total output amplitude for the channel from 0% to 1000% of the sum of the waveform amplitudes for that channel. The Total Channel Amplitude control display s that value. For instance, if the channel has 2 sine waveforms, one with an amplitude of 1 Vp, and the second with an amplitude of 3 Vp, and if the Channel Gain control is set to 50%, then Total Channe l Amplitude will display 2 Vp. In general, The A and B channels can have separate Channel Gains, however, if the A/B Lock checkbox is checked, the A and B values are always the same. If the sum of the waveform amplitudes exceeds the maximum output voltage of the generator, then the Channel Gain will automatically adjust to a value such that the total output amplitude reamains within range.

Auto-On affects the behavior of the generator output during a sweep

. If Auto-On is checked the

SR1 Operation Manual40

generator output will automatically turn on (if it was off) at the beginning of a sweep and turn off when the sweep is completed.

The large green/red On/Off buttons turn on and off their respective channels, while the Invert buttons invert the output for each channel.

Reference Controls

The Reference controls allow setting several parameters used in the computation of different generator amplitude units. See the Generator Units section for a complete description of all these units. Note that there is one set of referenc es for both generator channels.

Burst Controls

The SR1 Analog Generator implement s two different types of burst functionality. Sy nchronous Burst provides a burst sine wave with a variety of triggering options where the burst transitions are guaranteed to be synchronous with the zero crossings of the sine wave. This ty pe of burst is implemented in SR1 as a separate waveform. SR1 also offers the capability of bursting any waveform that can be configured in the generator, although with no guarantee that bursting will occur at zero-crossings. This type of burst will be referred to as "generator burst " as opposed to sync hronous burst.

Generator Burst Mode selects t he burst triggering mode

Timed The waveform outputs at the high amplitude then the low amplitude and repeats. The

total period is determined by the Burst Period control. The high-amplitude fraction of the period is determined by the Burst Duty Cycle.

Gated (hi) The waveform amplitude is determined by the TTL gating signal applied to the rear-

panel TTL burst trigger input. When the ext ernal signal is high the generator output is at

the high amplitude, when the external signal is lo the generator runs at the lo amplitude. Burst Period and Burst Duty Cycle are ignored.

Gated (lo) The waveform amplitude is determined by the TTL gating signal applied to the rear-

panel TTL burst trigger input. When the ext ernal signal is lo the generator output is at

the high amplitude, when the external signal is high the generator runs at the lo amplitude. Burst Period and Burst Duty Cycle are ignored.

Shaped Similar to Timed Burst ex cept that a c osine-squared window is applied to the signal

through the "hi" portion of the burst.

Triggered The output is zero until a TTL rising edge is detected at the rear panel burst trigger

input. The output then goes high for the interval specified by Burst Period.

Lo Amp selects the lo burst amplitude as a fraction of the original generator amplitude. For Triggered

SR1 Operation 41

Bursts the lo amplitude is fixed at zero.

Burst Pe riod controls the duration of triggered bursts and the total on/ off period for Timed and Shaped bursts.

Burst Duty Cycle c ontrols the fraction of the burst period during which the generator output is at the hi amplitude.

EQ Controls

Certain waveforms c an have their amplitudes s caled as a function of frequency according to the information contained in an EQ File. EQ files are XML files which specify a relative frequency respons e as a function of frequency by either interpolating a table of (frequency, respons e) pairs or by calculation from a set of pole and zero locations. The structure of EQ Files is detailed in the File Reference

section.

Use the

button to open a file dialog to spec ify the EQ File. Check the Invert EQ box to have the amplitude sc aled by the inverse of the EQ file respons e. W aveforms that are capable of being used with EQ files will have an "EQ" checkbox in their waveform tab. This box must be checked for EQ to be active regardless of whether an EQ file is selected in the file selection control. W hen an EQ file is selected and the checkbox is checked the amplitude control in the waveform tab will continue to s how the constant user-selected waveform amplitude, however, the Total Channel Amplitude control will display the amplitude with the EQ response included.

2.3.1.1

Analog Generator Units

The amplitude and frequency of generator waveforms can be spec ified using a variet y of units all of which are useful in different audio test scenarios. Because of the large number of waveforms that SR1 can generate and because it's useful to define amplitude in a way that simplifies the coupling between the details of the waveform and its amplitude, SR1 us es the following two conventions for analog generator amplitudes:

1. Analog generator amplitudes, regardless of the waveform or the units they are expressed in, refer to

the peak value of the waveform. W hen waveforms are combined in the generator, the amplitudes add simply, regardless of the phase relation of the waveforms.

2. RMS units always, regardless of waveform, have the same relat ion to peak units that they do for a

sine wave.

Thus, a square wave with instantaneous amplitude of ±1V is said to have an amplitude of 1 Vp, or .707 Vrms even though this is not the actual value of the RMS amplitude derived from a computation. While this may seem counterintuitive it simplifies the s pecification of amplitude units and is the c onvention used by most audio tes t equipment.

The following table desc ribes t he units available for setting the amplitude of analog generator waveforms.

Unit

Description

Vp Volts Peak, or s imply volts. (The p is added to reduce ambiguity with other volt-oriented

units ) An analog waveform with an amplitude of 1 Vp has an ins tantaneous peak value of 1 Volt.

Vrms A sine wave with an amplitude of 1.414 Vp has an RMS amplitude of 1 Vrms. In SR1,

SR1 Operation Manual42

Unit Description

Vrms and Vp always have this fix ed relationship. Irrespective of waveform, 1 Vrms = 1.414 Vp.

Vpp Similar to rms, Vpp (Volts peak-to-peak) has the same relation t o Vp that it does for a

sinewave. Thus, 1Vpp = .5 Vp.

dBVrms Decibels relative to 1 Vrms. A s ignal wit h an amplitude of -20 dBVrms has a peak

amplitude of 100 mVrms or 141.4 mVp.

dBu Decibels relative t o 0.7746 Vrms. Note that even though historically the value of 0.7746

Vrms was chosen because it represents the voltage required to dissipate 1 mW in a 600

load, in SR1 dBu specifies an open-circuit voltage without regard to the actual load

connected to the output.

dBr Decibels relative to the dBr Referenc e specified in the References Box.

dBm Decibels relat ive to 1 mW into a load specified by the dBm Reference in the References

Box. Specifying t he waveform amplitude in dB m asks SR1 to set the amplitude necessary

to deliver a certain amount of power to a specified load tak ing into account the output impedance of the generator. If the amplit ude is measured across the open-circuited output terminals with a high-impedanc e meter, you may get a different result.

W Watts into a load s pecified by the dBm Reference in the References Box. Specifying the

waveform amplitude in dBm asks SR1 to set the amplitude necessary to deliver a certain amount of power to a specified load taking into account the output impedance of the generator. If the amplitude is measured ac ross the open-circuited output terminals with a high-impedance meter, you may get a different result.

The value of "0" has no exact representation in dB units. When a generator amplitude of 0 is shown in a control displaying dB units the value "-1000 dB" is shown (which may display as "-1.0 kdB". This is not meant to imply an actual value of negative 1000 dB but merely to provide a convenient way to represent 0 in dB units.

Analog Generator Frequency Units

The following table desc ribes t he units used by SR1 in setting the frequency of digital generator waveforms. All frequency units except Hz mak e use of the Frequency Reference which is set in the

References Box

on the Analog Generator Panel.

Unit

Description

Hz The fundamental unit of frequency. 1 Hz = 1 cycle-per-second.

F/R Ratio relative to the Frequency Reference. A value of 3 F/R with reference of 2 kHz gives a

waveform frequency of 6 kHz.

dHz Difference relative to the Frequency Reference. A value of 500 dHz wit h a reference of 2

kHz gives a waveform frequency of 2.5 kHz.

%F re f Percent of the Frequency Reference. A frequency value of 50 %Fref with a reference value

of 10 kHz gives a waveform frequency of 5 kHz.

cents A "cent" is a logarithmic unit which represents 1/100 of a semit one of the musical scale.

12 semitones make up an octave. Thus a cent is 1/1200 of an octave.

octaves An octave is a factor of 2 in frequency. Thus, a frequency value of 3 octaves with a

reference of 1 kHz gives a waveform frequency of 8 kHz.

SR1 Operation 43

Unit Description

decades An decade is a factor of 10 in frequency. Thus, a frequency value of 2 decades with a

reference of 2 kHz gives a waveform frequency of 200 kHz.

2.3.1.2 Analog Generator Wave forms

SR1's Analog Generator is capable of generating an enormous variety of different audio waveforms, from simple ultra- lo-distortion sines to complex synchronous multitone waveforms. Because of its unique archit ecture which allows different waveforms to be combined the generator offers almost limit less flexibility in providing the perfect audio test output. In this section each waveform, the building blocks of the generator output, will be described in detail.

Sine Waveform Tab

When a waveform is added to the generator output using the Waveform Controls, the associated waveform tab shows up on t he generator panel. For inst ance, the Sine Waveform tab is shown above. If the Generator is in t he stereo output mode (separate waveforms for each channel) the tab title contains a channel designator indicating which channel the waveform is associated with. If the generator is in mono output mode, the channel designator is omitted and the title contains jus t the name of the waveform. Some of the controls found on the waveform tabs are common to many waveforms. These will be described first to avoid repetition.

Controls Common to Most Waveforms

The Waveform On c heckbox turns the selected waveform on and off. If the selected waveform is currently the only waveform in the generator, checking and unchecking this box has the same effect as turning on and off the generator using the Amplitude Controls

or by simply setting the waveform amplitude to zero and back. When the generator is outputting a combined waveform this checkbox allows the selected waveform to be toggled on and off while still outputting the remainder of the waveforms.

The EQ checkbox appears for only certain waveforms. If EQ is check ed, and an EQ file is selected on the generator panel, the actual generated amplitude for the waveform will be the nominal amplitude multiplied by the frequency response of the EQ file at the current frequency.

SR1 Operation Manual44

The Waveform Amplitude control sets the peak amplitude of most waveforms.

The Waveform Frequency control sets the frequency of many waveforms .

Generator Trigger

Certain generator waveforms c an generate a trigger, known as a "generator trigger" whic h can be used by the analyzers to synchronize the analyzer to a certain portion of the waveform. Triggering is a complex subject (which is fully described in the Analyzers

section), and there are many different possible analy zer trigger sources besides generator trigger, so in this section the disc ussion will be limited to those waveforms that provide generator triggers, and where in the waveform the trigger generated. When the generator is c onfigured with multiple waveforms, the first waveform whic h is generator-trigger capable will be the source of all generator triggers.

The Analog Generator Waveforms

In the following list, waveforms that may not be combined with other waveforms are marked with an asterisk (*) next to their names.

Normal Sine Low Distortion Sine*

The sine wave is the most basic audio test waveform. Sine waveforms are specified only by their amplitude and frequency. The Normal Sine waveform may be combined with other waveforms. The Low Dist ortion Sine waveform uses additional signal proces sing to obtain ultra-low distortion sine waves. Because this extra signal processing would interfere with other waveforms, the Low Distortion Sine may not be combined with other waveforms.

Low Distortion Sine and Phase

Due to the additional signal processing used to obtain ultra low distortion outputs, significant (~10º) phase differences may exist between the A and B channel outputs when the low distortion waveform is selected. For this reason it is not recommended to use low distortion sine for testing phase.

SR1 Operation 45

Phased Sine*

The phased sine waveform cons ists of two s ines, one on channel A and one on Channel B with a specified phase differenc e between them. This waveform may not be combined with other waveforms.

Synchronous Burst Sine*

The synchronous burst sine is a sinewave capable of fast s witching between two amplitude levels. Amplitude shifts occur synchronously with the zero-crossings of the sinewave . In addition to t he standard amplitude and frequency controls, the Synchronous Burs t Sine tab contains several controls which govern the burst options:

Burst Type selects the burst triggering mode

Internal The sine output alt ernates between the hi and lo amplitudes Both the hi and lo intervals

are integer numbers of cycles of the sine. The total period is determined by the Burst Rep. Ra te control. The Hi amplitude interval is determined by the Burst On Time

control.

Ext. Gated The waveform amplitude is determined by the TTL gating signal applied to the rear-

panel TTL burst trigger input. When the ext ernal signal is high the generator output is set to the high amplitude, when the ex ternal signal is lo the generator switches to the lo amplitude. Amplitude swit ching is performed synchronous with the sine zerocrossings regardless of the actual moment at which the external gating signal switches.

Ext. Triggered

The output is at the lo amplitude until a TTL rising edge is detected at t he rear panel burst trigger input. At the next zero c rossing the output then goes high for the number of cycles specified by Burst On Time .

Burst Repeti tion Rate is only valid for internal bursts. It sets the total on/off period of the burst cycle. The rate may be entered as a number of cycles, a frequency, or a time interval. In the latter two cases the value will be rounded to the nearest integer number of cycles.

Burst On Ti me . For internal bursts, Burst On Time specifies the number of cycles the sine is at the

SR1 Operation Manual46

high amplitude during the burst cycle. For externally triggered bursts the Burst On Time specifies the number of cycles the sine is output at the high amplitude following a trigger.

Lo Amplitude s pecifies the burst "Lo Amplitude" as a fraction of the nominal waveform amplitude.

Synchronous Burst Sine, Re petition Rate = 6 cycle s, Bur st On Time = 2cycle s

The green burst indicator will flash when the burst is triggered in either the Ext . Gated or Ext. Triggered modes. The red burst error indic ator will flash in the externally triggered mode to indicate a rate error condition.

Noise

The noise waveform outputs random nois e with an almost-gaussian amplitude probability density function with several options. (A true gaussian probability density function has finite probability for any amplitude, no matter how large, which is impractical for a physical device.)

Amplitude c ontrols , as with all SR1 waveforms, the peak value of the noise out put. The crest factor of the nois e waveform, the ratio of the peak value to the rms value of the nois e, is approximately 4.

The Repeat checkbox governs the repetition interval of the generated nois e. If not checked the repeat interval is sufficiently long that it won't observable under mos t conditions . If, however, it is desired for the noise to repeat after a fixed interval, check the Repeat box and enter the Repeat interval below it. If Repeat is selected, the noise waveform produces a generator trigger each time a waveform repeat is initiated.

The Pink checkbox specifies that the noise output should be filtered by a 3 dB/octave "pink ing" filter. While the power contained in a whit e noise signal is linearly proportional to the measurement bandwidth, pink noise will have equal power in equal logarithmic frequency intervals, e.g. the power contained in the 100 Hz to 200 Hz interval will be the same as the power contained in the 10 k Hz to 20 kHz interval.

White or Pink noise can be further filtered according to the c ontrols in the filter group.

SR1 Operation 47

Noise Filter

None White or Pink noise is directly output without further filtering.

Lowpa ss The white or pink noise is filtered with a 4th order Butterworth lowpass filter at the

frequency s pecified in the filter frequency control.

Highpass The white or pink noise is filtered with a 4th order Butterworth hipass filter at the

frequency s pecified in the filter frequency control.

1/3 Octa ve The white or pink noise is filtered wit h a 4th order 1/3 oc tave bandwidth Butterworth

bandpass filter at the frequency specified in the filter frequency c ontrol.

The noise waveform outputs a generator trigger when only when "Repeat" is checked. The trigger occurs each time the waveform is repeated.

MLS Noise

The MLS noise waveform output s a Maximum Length Sequenc e with a specified repetition interval and frequency profile. MLS waveforms are typic ally used as a stimulus in impuls e response measurements where several special properties of the MLS (the autocorrelation of an MLS sequence is a delt a function) simplify the calc ulation of the impulse response. Because SR1 uses a full 2-channel FFT analyzer to make impulse response measurements it is not necessary to use MLS noise as a stimulus— any broadband signal will work. Nevertheless SR1 includes the MLS waveform because of its his toric al association with impulse response measurements.

Amplitude c ontrols , as with all SR1 waveforms, the peak value of the noise out put. The crest factor of the MLS waveform, which is essentially a square wave, is close to 1.

The Length selection controls the length of the MLS sequence. Selecting "13," for example, chooses an MLS s equence whose repetition interval is 2

13

-1 samples.

The Pink checkbox specifies that the noise output should be filtered by a 3 dB/octave "pink ing" filter. While the power contained in a whit e noise signal is linearly proportional to the measurement bandwidth, pink noise will have equal power in equal logarithmic frequency intervals, e.g. the power contained in the 100 Hz to 200 Hz interval will be the same as the power contained in the 10 k Hz to 20 kHz interval.

The MLS noise waveform output s a generator trigger each t ime the MLS cycle repeats.

SR1 Operation Manual48

USASI Noise*

USASI noise is a special type of filtered noise designed to mimic the content of audio program material. USASI noise is typically used in testing broadcast transmitters to measure compliance with transmission bandwidth requirements . Because the frequency c ontent of USASI noise is fixed, only an amplitude control appears on the waveform tab. USASI noise may be used in conjunction with generator

bursting

to generate a burst USASI signal suit able for transmitter testing.

Freque ncy Spe ctrum of USASI Noise : 100 Hz 6dB/oct hipas s + 320 Hz 6 dB/oct lopass

Square Wave*

SR1 square waves us es special hardware to generate clean analog square waves. As a result, s quare waves may not be combined with other waveforms in the analog generator. The square wave frequency is limited to a maximum of 50 kHz regardless of the selected analog generator sampling rate. Because of the finit e bandwidth of the analog generator, square waves will have finite risetime and overshoot depending on the frequency and the s elected D/A converter.

SR1 Operation 49

Ramp

The ramp waveform cons ists of repetitive runs of integer numbers of "rising" and "falling" samples to produce triangle-like output waveforms. Because the runs are restricted to integer number of samples, the Ramp Frequency and Ramp Fractional Rise Time have limited resolution which is a function of the selected generator sample rate. The lowest amplitude sample has the value assigned in the Low

Amplitude c ontrol. The highest amplitude s ample has the value given in the High Amplitude c ontrol.

1 kHz Ramp with Vm ax=+1,Vmin=-1,25% Rise Tim e

The ramp waveform generates a generator trigger each time the ramp begins its rising segment.

Arbitrary Waveform

The arbitrary waveform plays a sequence of values found in a user supplied table. Arbitrary waveform files are simple ASCII files with one or more columns of floating point numbers representing t he values of the

SR1 Operation Manual50

arbitrary waveform at each sampling interval.. Use t he button to open a file dialog to select an arbitrary waveform file. If multiple columns are detected in the file, SR1 displays a dialog asking whic h column to load. The number of points read from the table is then displayed in the corresponding control.

The amplitude entered in the Arb amplitude control is assigned t o the max imum value found in the table. The absolute s caling of the table values does not affec t the output waveform. Thus t he following table of values in the file:

0, 0.1, 0.2, 0.3, 0.4, 0.5,

produces a linear ramp from 0 to 2.0 Vrms if the amplitude control is set to 2.0 Vrms. The maximum amplitude for arbitrary waveforms is half that of sinewaves due to the fact that non-bandlimited arbitrary waveforms may ex hibit overshoot.

The Output Rate control governs how fast table points are output. At 100% the output rate is 1 table point per output sample. At 200% the generator skips a table point and outputs every other table point each output sample. For fractional output rates the waveform is interpolated. So at 50% Output Rate the generator outputs a table point, then and interpolated point and then the next table point. Bandlimited interpolation is used where memory allows. Otherwise linear interpolation is used. A maximum table length of 128 kpoints is allowed, subject to other waveforms or instrument features us ing the DSP memory.

The arbitrary waveform generates a generator trigger each time the output returns to the beginning of the t able.

FFT Chirp

The FFT Chirp waveform is designed to work in combination with one of SR1's FFT Analyzers. The c hirp waveform provides a tone ex actly at the bin c enter of each the FFT Analyzer's analysis bins. In the default case, each tone has equal amplitude, however, the Chirp waveform can be us ed with generator

EQ to generate chirp signals with custom tailored frequency response.

Chirp signals are useful for quickly measuring the frequency response of a device under test . Unlike noise signals which are not deterministic and require long averaging times to measure frequency response, a chirp signal can precisely measure frequency response in a single FFT record.

The Chirp waveform is sync hronized to the settings of a partic ular FFT analyzer. If the resolution or frequency s pan of that analyzer changes, the chirp waveform automatically reconfigures to provide a full set of bin-center tones. If t he corresponding analyz er is set to "show aliased lines

" the chirp outputs a tone in every single FFT bin, from near DC to Fs/2. If "show aliased lines " is off, the chirp outputs tones from near DC up to the alias limit for the analyzer's selected converter and frequency span. See the FFT

SR1 Operation 51

Analy zer section for more details on these topics. Becaus e of the sy nchronous nature of the chirp

signal, a uniform window should be selected in the analyzer when using the chirp waveform.

Selec tion of the associated FFT Analyz er is done with the Chirp Source control.

Chirp Source Associated Analyzer

A0: FFT1 Analyzer 0, Single Channel FFT Analyzer

A0: FFT2 Analyzer 0, Dual Channel FFT Analy zer

A1: FFT0 Analyzer 1, Single Channel FFT Analyzer

A1: FFT1 Analyzer 1, Dual Channel FFT Analy zer

Synchronous chirp generation requires there to be a relationship between the selected generator sampling frequency and the ass ociated analyzer sampling frequency. In general, the two frequencies need to be eit her exactly the same or some integer multiple of one another. If the generator and analyzer sampling frequencies are incompatible, the "Compliance" led will glow red and no waveform will be output. The compliance led may also show red if SR1 runs out of table memory to create a long chirp signal (say for a large number of FFT lines, or when large amounts of fft zoom are used. The chirp waveform may attempt to use interpolation in situations when not enough memory is available for the complete table, in which case the "Compliance" led will glow yellow. Some degradation of flatness c an be expected in this c ase.

Using t he chirp signal it is possible to make cross domain measurements of both amplitude and phase. For instance when testing a D/A c onverter a chirp can be output in the digital domain, and the D/A frequency res ponse and phase recorded in the analog domain. To ensure cross-domain sampling rate compatibility use the following sampling rate selections for the generator and analyzer.

Type of Mea surement Ge nerator Fs Analyzer Fs

Analog Source, Digital Measurement (ADC)

Selec t Digital ISR as the analog generator Fs.

Selec t Digital as the Analyzer s ource which aut omatically choos es ISR as the analy zer Fs.

Digital Source, Analog Measurement (D/A)

Selec t the desired digital audio output frequency using the Digital I/ O panel.

Selec t the Analog Hi-Res converter on the analy zer panel and set the Hi-Res converter Fs to Digital OSR or digital OSRx2 using the Analog Inputs panel.

Because the sync hronous chirp source has a time-dependent amplitude profile, it may fool the input aut oranging cont rol into switching ranges too frequently. Depending on the FFT bandwidth (which determines the chirp length) it may be us eful to turn off input autoranging when using the synchronous chirp signal.

For the s ame reason, be sure to select the " Uniform" window when using the synchronous chirp. Window functions attenuate the beginning and the end of the timre record for the FFT analyzers which when using the chirp means that certain frequencies will be attenuated more than others. This destroy s the "flat" nature of the synchronous chirp signal.

Using Chirp With Eq and Inverse Eq

By using the EQ feature of the generator it is possible to tailor a stimulus with a precisely defined frequency profile. EQ files spec ify a relative frequency response as a function of frequency. The format of EQ files is described in the SR1 File Reference

. W hen an EQ file is on the Configuration tab of the generator panel, the amplitude in each frequency bin will be multiplied by the frequency response of the EQ file at that frequency. If t he "Invert EQ" checkbox is c hecked, the amplitude in each bin will be

SR1 Operation Manual52

multiplied by the inverse of the frequency response of the EQ file.

When EQ is selected with chirp, the "Variable Sweep Rate" feature is enabled. Selecting Variable Sweep Rate c hanges the chirp sweep rate to equalize the time domain amplitude in a chirp with variable frequency domain amplitude.

For instance, the graph above shows the time response of a chirp weighted with the CCIR EQ curve. The yellow trace was taken with Variable Sweep rate off, and the green with Variable Sweep Rate on. Even though the two chirps have identical amplitudes in the frequency domain notice how more uniform and how much lower the crest factor the variable sweep rate chirp has. The lower crest factor makes it much more suitable waveform for audio testing.

The chirp waveform outputs a generator trigger once each cycle. Be sure to use generator trigger as the analy zer trigger source when using the c hirp waveform with the FFT analyzer.

Log-sine Chirp*

The log-sine chirp waveform is designed to work in c ombination the dual-channel FFT analyzer to make impulse respons e measurements. The log-sine chirp waveform is a sinusoid whose frequency is swept in a logarithmic fashion over the frequency span of its ass ociated FFT analyz er. The log-sine chirp waveform has a "pink" frequency roll off of 3 dB/oct.

The log-sine chirp waveform is synchroniz ed to the settings of a particular FFT analyzer. If the resolution or frequency s pan of that analyzer changes, the log-sine chirp waveform automatically reconfigures to

SR1 Operation 53

sweep over the frequency span of the selected analyzer. Because of the synchronous nature of the c hirp signal, a uniform window should be selected in the analyzer when using the log-sine chirp waveform.

Selec tion of the associated FFT Analyz er is done with the Chirp Source control.

Chirp Source Associated Analyzer

A0: FFT1 Analyzer 0, Single Channel FFT Analyzer

A0: FFT2 Analyzer 0, Dual Channel FFT Analy zer

A1: FFT0 Analyzer 1, Single Channel FFT Analyzer

A1: FFT1 Analyzer 1, Dual Channel FFT Analy zer

If the analyz er span is set to frequencies which are unreachable with the current generator sampling the "Compliance" led will glow red and no waveform will be output.

Be sure to select the "Uniform" window when using the log-sine c hirp. W indow functions attenuate the beginning and the end of the time record which means that some frequencies will be attenuated more than others by the window.

The advantages using log-sine chirps for impulse response measurements are detailed by Miller and Massarini ("Transfer Function Meas urements with Sweeps", J. Audio Eng. Soc., vol. 49, pp. 443-471, June 2001.) They report better results us ing log-sine stimulus compared to MLS s timulus for a wide range of audio DUTs. One particular advantage concerns the unique ability of the log-sine chirp to differentiate between the linear and non-linear portions of the DUT response. Because of the properties of the group delay of the log-sine chirp waveform, harmonic responses appear offs et in time relative to the linear response. This can be clearly s een in this impulse response measurement of a consumer stereo amplifier:

When t he purely linear response is gated and transformed bac k into the frequency domain a much better measurement of the DUT frequency response is obtained. (This is detailed in the FFT2 analyzer discuss ion. See "Meas urement of audio equipment with log-swept sine chirps", by Thomas Kite, Presented at the 117th AES Convention, San Francisco, CA, October 2004 for a concise explanation of the unique group-delay properties of the log-sine chirp.)

The log-sine chirp waveform outputs a generator trigger at the beginning of each FFT time record. Be sure to use generator trigger as the analyzer trigger source when using the logsine chirp waveform with the FFT analyzer.

SR1 Operation Manual54

MultiTone*

Like FFT Chirp, the MultiTone Waveform is a special waveform containing a series of tones that are generated in s ynchronous fashion to ensure bin-center plac ement in the MultiTone Analyzer

. Using the MultiTone generator and analyz er many different characteristics of a device—nois e, distortion, frequency response, can be measured quic kly and simultaneous ly without the need for multiple swept measurements.

All of the details of the multitone waveform— tone frequency and amplitude, phase, etc . are configured using the MultiTone Configuration Panel

. As a result, only the amplitude is specified on the waveform tab. The Export button allows t he current multitone waveform to be saved in arbitrary waveform format for off-line analys is. Because of the special properties of the MultiTone waveform it may not be combined with other waveforms. The Multitone waveform cannot be selected from the analog generator panel unless the MultiTone configuration panel specifies the use of the analog generator.

The MultiTone waveform outputs a generator trigger once eac h cycle. When performing multitone analysis with the local SR1 generator be sure to use generator trigger as the analyzer trigger s ource to ensure proper phase calibration.

IMD Waveform*

IMD Tab for SMPTE/DIN

And for CCIF

The IMD Waveform can be configured to output the three classic audio IMD tes t signals— SMPTE, CCIF, and DIM.

SR1 Operation 55

IMD Type

SMPTE/DIN Combines a High Frequency Sinewave with a low frequency sinewave. For a generator Fs

of 512 kHz t he low frequency can be set between 10 Hz and 1 k Hz. The High Frequency can be anywhere down to 5x the low frequency. The Amplitude Ratio (low freq/high freq) can be set to either 1:1 or 4:1 with the Amplitude Ratio control.

CCIF/DFD Two sines centered around the Center Frequency separated in frequency by the IM

frequency. The amplitude ratio is fixed at 1: 1.

DIM B Outputs a ~14 kHz sinewave and ~2.96

kHz squarewave. Squarewave is filtered with a s ingle pole 30 k Hz filter.

For all the DIM options the ratio of the squarewave to sinewave peak-to-peak amplitudes is 4:1. Because the s quarewave needs to be "perfect" frequency, with an exactly equal number of positive and negative samples, the exac t squarewave frequency is chosen by the generator, depending on t he generator Fs, to be as close as possible to the squarewave frequenc y given by the standard. The sinewave frequency is then s et in the same ratio to the squarewave frequency as would be for the signals in the standard.

DIM 30 Outputs a ~15 kHz sinewave and ~ 3.15

kHz squarewave. Squarewave is filtered with a s ingle pole 30 k Hz filter.

DIM 100 Outputs a ~15 kHz sinewave and ~ 3.15

kHz squarewave. Squarewave is filtered with a s ingle pole 100 k Hz filter.

IMD tab for DIM selection

In all cases the Total Amplitude control sets the c ombined amplitude of all signals .

The IMD waveform is designed to be used with the IMD analyzer. The analyzer automatically determines the type of IMD signal is being generated and automat ically configures itself for the correct analysis. See the IMD Analyzer

section for more details.

Polarity Check Waveform

SR1 Operation Manual56

The polarity check waveform uses a phased combination of two sine waves to produce a deliberately asymmetric waveform that points "up". When this waveform is applied to a device under test it is easy to see if the devic e properly maintains or inverts polarity by checking the output waveform us ing the time record of the FFT Analyzer

. If the output waveform still points "up" the device maintains polarity. If the

waveform points "down" the device is inverting.

Polarity Wavefor m Non-Inve rted

...And Inverted

Constant (Offset)

The constant waveform simply adds a DC offs et to the output. The offset can be set anywhere over the full positive and negative range of the generator output. Offset waveforms take up space in the generator's D/A converter and reduce the resolution available to ot her waveforms. For the best distortion and noise keep the offset as small as possible.

SR1 Operation 57

2.3.2 Digital Generator Panel

The Digital Generator Panel controls the operation of SR1's digital audio generator. The generator can be populated with many different waveforms— sines, square waves, ramps, etc. Many of the waveforms can be combined by the generator. For instanc e, if the generator is populated with sinewave and noise, than the output will be the sum of the sinewave and noise signals. The amplitudes of each component of the composite signal are adjustable separately as is the overall amplitude of the combined signal. Some waveforms, (USASI noise, for instance) are special-purpose test signals and may not be combined with other waveforms.

The tabs corresponding to each particular waveform are described in the Digital Generator W aveforms section. This sec tion des cribes the controls and settings of the digital generator that are relevant to all waveforms.Note that the controls on the generator panel and the waveform tabs are mainly c oncerned with the properties of the embedded digit al audio output— controls which govern the properties of the digital audio carrier signal are found on the Digital I/O

panel.

The SR1 Digital Generator is separate and independent from the Analog Generator. The two generators operate simultaneously and independently with different waveforms. The two generators, however, do share memory used for arbitrary waveforms and FFT chirps. Deleting an arbitrary waveform in the analog generator mak es memory available for the digital generator and vice versa.

Output Controls

Mode c ontrols the output mode of the Digital Generator.

Mono The same waveform is output to both the A and B channels. The amplitude of each

channel is still separately adjus table, but the waveform is the same.

Stereo Each channel can be configured with a different waveform.

SR1 Operation Manual58

Dither c ontrols the type of dither us ed by the Digital Generator. The digital generator generates the waveform internally with higher precision than the maximum 24-bit digital output word. Noise with the selected probability distribution is added to the internal representation, and the result is truncated to the width s pecified in the Digital I/O Output Resolution control.

Off No dither is used in calculating the output word.

Triangular Dither with a triangular probability distribution and a width of ±1 lsb is added to the

signal.

Rectangular Dither with a rectangular probability distribution and a width of ±1/2 lsb is added to the

signal.

Fs displays the current generator output sampling rate. This value is c hosen on the Digit al I/O panel.

Waveform Controls

The New button displays the Waveform Selection Submenu.

The selected waveform will either be added to the output for one or both channels depending on the Mode setting. Certain waveforms (for instance USASI Noise) cannot be combined with other waveforms. When one of these waveforms is selected all of the current waveforms are deleted. Other waveforms simply add t o the current output when selected. See the Digit al Audio Waveform

section for a detailed

description of all available waveforms.

The Delete button deletes the currently selected waveform.

The A/B selection buttons only appear when the generator Mode is set to Stereo. The buttons determine which channel a newly added waveform will appear on. When the mode is c hanged to stereo, any waveforms present will be assigned to channel A. When the mode is changed from stereo to mono, all channel B waveforms are deleted and the channel A waveforms are output on both channels.

SR1 Operation 59

Amplitude Controls

The Channel Gain control varies modifies the total output amplitude for the channel from 0% to 1000% of the sum of the waveform amplitudes for that channel. The Total Channel Amplitude control display s that value. For instance, if the channel has 2 sine waveforms, one with an amplitude of .3 FFS, and the second with an amplitude of .5 FFS, and if the Channel Gain control is set to 50% , then Total

Channel Amplitude will display .4 FFS. In general the A and B channels can have separate Channe l Gains, however, if the A/B Lock checkbox is checked, the A and B values are always the same. Auto- On affects the behavior of the generator output during a sweep

. If Auto-On is checked the generator

output will automatically turn on at the beginning of a sweep (if it was turned off) and turn off when the sweep is completed.

The large green/red On/Off buttons turn on and off their respective channels, while the Invert buttons invert the output for each channel.

Reference Controls

The Reference controls allow setting several parameters used in the computation of different generator amplitude units. See the Digital Generator Units

section for a complete description of all these units.

Note that there is one set of references for both generator channels.

Burst Controls

The SR1 Digital Generator implements a Timed Burst mode which switches the overall amplitude of the combined waveform output between two different values.

Burst Mode turns the burst feature on and off.

Lo Amp selects the lo burst amplitude as a fraction of the original generator amplitude.

Burst Pe riod controls the total hi+lo period of the burst cycle. This value may be entered in seconds or

in cycles of the current waveform.

Burst Duty Cycle c ontrols the fraction of the burst period during which the generator output is at the hi amplitude.

SR1 Operation Manual60

Burs t Digital Noise, Period = 20 ms , Duty Cycle = 25%

Lo Amplitude = 10%

EQ Controls

Certain waveforms c an have their amplitudes s caled as a function of frequency according to the information contained in an EQ File. EQ files are XML files which specifiy a relative frequency response as a function of frequency by either interpolating a table of (frequency, respons e) pairs or by calculation from a set of pole and zero locations. The structure of EQ Files is detailed in the File Reference

section.

Use the

button to open a file dialog to spec ify the EQ File. Check the Invert EQ box to have the amplitude sc aled by the inverse of the EQ file respons e. W aveforms that are capable of being used with EQ files will have an "EQ" checkbox in their waveform tab. This box must be checked for EQ to be active regardless of whether an EQ file is selected in the file selection control. W hen an EQ file is selected and the checkbox is checked the amplitude control in the waveform tab will continue to s how the constant user-selected waveform amplitude, however, the Total Channel Amplitude control will display the amplitude with the EQ response included.

2.3.2.1

Digital Generator Units

The amplitude and frequency of generator waveforms can be spec ified using a variet y of units all of which are useful in different audio test scenarios. Because of the large number of waveforms that SR1 can generate and because it's useful to define amplitude in a way that simplifies the coupling between the details of the waveform and its amplitude, SR1 us es the following two conventions for digital generator amplitudes:

1. Digital generator amplitudes , regardles s of the waveform or the units t hey are expressed in, refer to

the peak value of the waveform. W hen waveforms are combined in the generator, the amplitudes add simply, regardless of the phase relation of the waveforms.

2. RMS and Peak-to-peak unit s always, regardless of waveform, have the same relation to peak units

that they do for a sine wave. In other words, think of rms and peak-to-peak units as s imply units with a a fixed scale relative to peak units rather than as a quantity derived through a calc ulation on the waveform.

The following table desc ribes t he units available for setting the amplitude of digital generator waveforms.

SR1 Operation 61

Unit Description

FFS According to AES17-1998 (r2004), "Full-scale amplitude is the amplitude of a 997 Hz

sinewave whose positive peak value reaches the positive digital full scale leaving the negative maximum code unused." The FFS (Fraction Full Scale) unit expresses the peak amplitude of any SR1 generator waveform relative to this definition of full-sc ale amplitude. When dither is on, full scale amplitude is reduced s ymmetrically by 1 bit to allow for dither. Small values of FFS may be expressed as mFFS (milli-FFS) or uFFS (microFFS).

%F S Same as FFS (above) but ex pressed as a percentage of full-scale amplitude. 50 %FS = .5

FFS.

Vrms This digital waveform amplitude unit is directly convertible to FFS depending on the value

of the V FS (Volts Full Scale) set in the references

section of the digital generator panel.. If the value of V FS is 2 Vrms, for instance, then an amplitude of 1 Vrms corresponds to an amplitude of .5 FFS. These units allow digital amplitudes to be ex pressed as analog voltages as is often useful when working with D/A converters where the V FS value can be thought of as the DAC's full scale output volt age.

Vp This unit of digital wave form amplitude is convertible to FFS depending on the value of the

V FS (Volts Full Scale) reference

and the fixed relations hip of peak voltage to rms voltage for a sinewave. If the value of V FS is 1 Vrms, for instance, then an amplitude of 1.414 Vp would correspond to an amplitude of 1 Vrms which in turn would correspond to an amplitude of 1 FFS.

Vpp This unit of digital wave form amplitude is convertible to FFS depending on the value of the

V FS (Volts Full Scale) reference

and the fixed relations hip of peak voltage to peak -topeak voltage for a sinewave. If the value of V FS is 1 Vrms , for instance, then an amplitude of 2.0 Vpp would correspond to an amplitude of 1 Vrms which in turn would correspond to an amplitude of 1 FFS.

dec The peak value of the waveform expressed as a decimal code. The convers ion of decimal

code to FFS depends on the setting of the Output Resolution in the Digital I/O

panel. For

the default 24-bit output resolution setting 1FFS = 2

23

-1 = 8,388,607 dec.

hex The peak value of the waveform expressed as a hexadec imal code. The conversion of

hexidecimal code to FFS depends on the set ting of the Output Resolution in the Digital I/

O panel. For the default 24-bit output resolution setting 1FFS = 223-1 = 0x 7fffff hex.

dBFS Decibels relative to the full scale amplitude definition. (See FFS above) For instance, 0.1

FFS = -20 dBFS. (20*log10(0.1))

dBV Decibels relative to the Vrms value calculated with the V FS (Volts Full Scale) reference

set in the digital generator panel. For example, with a V FS value of 2 Vrms an amplitude of -20 dBVrms corresponds to .1 Vrms which in turn corresponds to an amplitude of 0.05 FFS.

dBu Decibels relative t o 0.7746 Vrms. (Hiistorically the value of 0.7746 Vrms represents the

voltage required to dissipate 1 mW in a 600

load.) If V FS is s et to 1 Vrms than an

amplidue of 0 dBu correesponds to 0.7746 which in turn corresponds to 0.7746 FFS.

dBr Decibels relative to the dBr reference set in the references section of the digital generator

panel. The dBr reference is always set in units of FFS. Thus, with the dBr reference set to .5 FFS, an amplitude of 0 dBr corresponds to .5 FFS.

Bits Computed from dBFS using the relation bits = 1.76 + (dBFS/6.02). For instance, half

scale (-6.02 dBFS) is 0.76 bits.

Digital Generator Frequency Units

The following table desc ribes t he units used by SR1 in setting the frequency of analog generator

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waveforms. All frequency units except Hz mak e use of the Frequency Reference which is set in the References Box on the

Digital Generator Panel.

Unit

Description

Hz The fundamental unit of frequency. 1 Hz = 1 cycle-per-second.

F/R Ratio relative to the Frequency Reference. A value of 3 F/R with reference of 2 kHz gives a

waveform frequency of 6 kHz.

dHz Difference relative the Frequency Reference. A value of 500 dHz with a reference of 2 kHz

gives a waveform frequency of 2.5 kHz.

%F re f Percent of the Frequency Reference. A frequency value of 50 %Fref with a reference value

of 10 kHz gives a waveform frequency of 5 kHz.

cents A "cent" is a logarithmic unit which represents 1/100 of a semit one of the musical scale.

12 semitones make up an octave. Thus a cent is 1/1200 of an octave.

octaves An octave is a factor of 2 in frequency. Thus, a frequency value of 3 octaves with a

reference of 1 kHz gives a waveform frequency of 8 kHz.

decades An decade is a factor of 10 in frequency. Thus, a frequency value of 2 decades with a

reference of 2 kHz gives a waveform frequency of 200 kHz.

2.3.2.2 Digita l Ge ne ra tor W aveforms

SR1's Digital Generator is capable of generating an enormous variety of different audio waveforms, from simple sines to complex synchronous multitone waveforms . Because of it s unique architec ture which allows different waveforms to be combined the generator offers almos t limitless flexibility in providing the perfect audio test output. In this section each waveform, t he building blocks of the generator output, will be described in detail.

Sine Waveform Tab

When a waveform is added to the generator output using the Waveform Controls, the associated waveform tab shows up on t he generator panel. For inst ance, the Sine Waveform tab is shown above. If the Generator is in t he stereo output mode (separate waveforms for each channel) the tab title contains a channel designator indicating which channel the waveform is associated with. If the generator is in mono output mode, the channel designator is omitted and the title contains jus t the name of the waveform. Some of the controls found on the waveform tabs are common to many waveforms. These will be described first to avoid repetition.

Controls Common to Most Waveforms

The Waveform On c heckbox turns the selected waveform on and off. When the generator is outputting

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a combined waveform this checkbox allows the selected waveform to be toggled on and off while still outputting the remainder of the waveforms.

The EQ checkbox appears for only certain waveforms. If EQ is check ed, and an EQ file is selected on the generator panel, the actual generated amplitude for the waveform will be the nominal amplitude multiplied by the frequency response of the EQ file at the current frequency.

The Waveform Amplitude control sets the peak amplitude of most waveforms in one of the digital

generator amplitude units. Becaus e generator amplitudes refer to peak waveform values, amplitudes

cannot exceed 1 FFS regardles s of waveform.

The Waveform Frequency control sets the frequency of many waveforms in one of the digital generator

frequency units. Digital generator frequencies range from 10 Hz up to Fs/2 where Fs is the current digital

output sampling rate (OSR). The current OSR is display ed at the top of the digital generator panel.

Generator Trigger

Certain generator waveforms c an generate a trigger, known as a "generator trigger" whic h can be used by the analyzers to synchronize the analyzer to a certain portion of the waveform. Triggering is a complex subject (which is fully described in the Analyzers

section), and there are many different possible analy zer trigger sources besides generator trigger. In this sec tion the discuss ion of triggering will be limited to those waveforms which provide generator triggers, and where in those waveform is t he trigger occurs. When the generator is configured with multiple waveforms , the first waveform which is generator-trigger capable will be the source of all generator triggers.

The Digital Generator Waveforms

In the following list, waveforms that may not be combined with other waveforms are marked with an asterisk (*) next to their names.

Sine

The sine wave is the most basic audio test waveform. Sine waveforms are specified only by their amplitude and frequency. The Normal Sine waveform may be combined with other waveforms.

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Phased Sines*

The phased sine waveform cons ists of two s ines, one on channel A and one on Channel B with a specified phase differenc e between them. This waveform may not be combined with other waveforms. Phases may be entered in any 360º interval (for instance 0º to 360º or -180º to 180º) specified on the

Preferences Panel

.

Noise

The noise waveform outputs random nois e with an almost-gaussian amplitude probability density function with several options. (A true gaussian probability density function has finite probability for any amplitude, no matter how large, which is impractical for a physical device.)

Amplitude c ontrols , as with all SR1 waveforms, the peak value of the noise out put. The crest factor of the nois e waveform, i.e. the ratio of the peak value to the rms value of the nois e, is approximately 4.

The Repeat checkbox governs the repetition interval of the generated nois e. If not checked the repeat interval is sufficiently long that it won't observable under mos t conditions . If, however, it is desired for the noise to repeat after a fixed interval check the Repeat box and enter the Repeat interval below it.If Repeat is selected, the noise waveform produces a generator trigger each time a waveform repeat is initiated.

The Pink checkbox specifies that the noise output should be filtered by a 3 dB/octave "pink ing" filter. While the power contained in a whit e noise signal is linearly proportional to the measurement bandwidth, pink noise will have equal power in equal logarithmic frequency intervals, e.g. the power contained in the 100 Hz to 200 Hz interval will be the same as the power contained in the 10 k Hz to 20 kHz interval.

White or Pink noise can be further filtered according to the c ontrols in the filter group.

Noise Filter

None White or Pink noise is directly output without further filtering.

Lowpa ss The white or pink noise is filtered with a 4th order Butterworth lowpass filt er at the

frequency s pecified in the filter frequency control.

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Highpass The white or pink noise is filtered with a 4th order Butterworth hipass filter at the

frequency s pecified in the filter frequency control.

1/3 Octa ve The white or pink noise is filtered wit h a 4th order 1/3 oc tave bandwidth Butterworth

bandpass filter at the frequency specified in the filter frequency c ontrol.

MLS Noise*

The MLS noise waveform output s a Maximum Length Sequenc e with a specified repetition interval and frequency profile. MLS waveforms are typic ally used as a stimulus in impuls e response measurements where several special properties of the MLS (the autocorrelation of an MLS sequence is a delt a function) simplify the calc ulation of the impulse response. Because SR1 uses a full 2-channel FFT analyzer to make impulse response measurements it is not necessary to use MLS noise as a stimulus— any broadband signal will work. Nevertheless SR1 includes the MLS waveform because of its his toric al association with impulse response measurements.

Amplitude c ontrols , as with all SR1 waveforms, the peak value of the noise out put. The crest factor of the MLS waveform, which is essentially a square wave, is close to 1.

The Length selection controls the length of the MLS sequence. Selecting "13," for example, chooses an MLS s equence whose repetition interval is 2

13

-1 samples.

The Pink checkbox specifies that the noise output should be filtered by a 3 dB/octave "pink ing" filter. While the power contained in a whit e noise signal is linearly proportional to the measurement bandwidth, pink noise will have equal power in equal logarithmic frequency intervals, e.g. the power contained in the 100 Hz to 200 Hz interval will be the same as the power contained in the 10 k Hz to 20 kHz interval.

USASI Noise*

USASI noise is a special type of filtered noise designed to mimic the content of audio program material. USASI noise is typically used in testing broadcast transmitters to measure compliance with transmission bandwidth requirements . Because the frequency c ontent of USASI noise is fixed, only an

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amplitude control appears on the waveform tab. USASI noise may be used in conjunction with generator

bursting

to generate a burst USASI signal suit able for transmitter testing.

Freque ncy Spe ctrum of USASI Noise : 100 Hz 6dB/oct hipas s + 320 Hz 6 dB/oct lopass

Square Wave

Perfect digital square waves (equal integer numbers of up and down samples) are possible only for a limited number of frequencies for each digit al OSR. If Precision Frequencies is chec ked, square wave frequencies will be limited to these "perfect" frequencies. If Precis ion Frequencies is unchec ked, the digital generator will interpolate a square wave at any frequency with significantly less fidelity t o an ideal square wave.

Ramp

The ramp waveform cons ists of repetitive runs of integer numbers of "rising" and "falling" samples to produce triangle-like output waveforms. Because the runs are restricted to integer number of samples, the Ramp Frequency and Ramp Fractional Rise Time have limited resolution which is a function of the selected generator sample rate. The lowest amplitude sample has the value assigned in the Low

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Amplitude c ontrol. The highest amplitude s ample has the value given in the High Amplitude c ontrol.

The ramp waveform generates a generator trigger each time the ramp begins its rising segment.

Arbitrary Waveform

The arbitrary waveform plays a sequence of values found in a user supplied table. Arbitrary waveform files are simple ASCII files with one or more columns of floating point numbers representing t he values of the

arbitrary waveform at each sampling interval.. Use t he

button to open a file dialog to select an arbitrary waveform file. If multiple columns are detected in file, SR1 displays a dialog asking which column to load. The number of table points read from the table is then displayed in the corresponding control.

The amplitude entered in the Arb amplitude control is assigned t o the max imum value found in the table. The absolute s caling of the table values does not affec t the output waveform. However, when operating at arbitrary output rates the SR1 interpolates t he user supplied table and normalizes to the peak interpolated value thereby insuring that the peak amplitude remains constant at different output rates. Thus the following table of values in the file:

0, 0.1, 0.2, 0.3, 0.4, 0.5,

produces a linear ramp from 0 to 0.2 FFS if the amplitude control is set to 0.2 FFS.

The Output Rate control governs how fast table points are output. At 100% the output rate is 1 table point per output sample. At 200% the generator outputs every other table point each output sample. For fractional output rates the waveform is interpolated. So at 50% Output Rate the generator outputs a table point, then and interpolated point and then the next table point.

The arbitrary waveform generates a generator trigger each time the output returns to the beginning of the t able.

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