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DigiPro DA795
Operation Manual
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Sencore DigiPro DA795 Operation Manual

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DA795
DigiPro
Digital Audio Analyzer
Operation Manual
(Firmware version 1.17)
3200 Sencore Drive, Sioux Falls, SD 57107
http://www.sencore.com mailto:sales@sencore.com 1.800.736.2673 or 1.605.339.0100
WARNING
PLEASE OBSERVE THESE SAFETY PRECAUTIONS
There is always a danger present when using electronic test equipment.
Unexpected voltages can be present at unusual locations in defective
equipment and distribution systems. Become familiar with the equipment
with which you are working, and observe the following safety precautions.
Every precaution has been taken in the design of the DigiPro DA795 Digital Audio Analyzer to insure that it is as safe as possible. However, safe operation depends on you, the operator.
1. Never exceed the limits of the DigiPro DA795 as given in the specifications
section or other special warnings provided in this manual.
2. Always be sure that your equipment is in good working order. Broken or
frayed test leads or cables can be extremely dangerous and may expose you to high voltages.
3. Remove test leads immediately following measurements to reduce the
possibility of shock.
4. Do not work alone when working under hazardous conditions. Always have
another person available in case of an accident.
5. Never assume that a cable shield is at earth ground potential. Both static
and electrical voltages can be present on a cable’s sheath.
6. Always follow standard safety procedures.
When in doubt, be careful.
Sencore reserves the right to make changes in specifications and other information contained in this publication without prior notice, and the reader should in all cases consult Sencore to determine whether any such changes have been made. This manual may not be reproduced, and is intended for the exclusive use of Sencore users.
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DA795
DigiPro
Digital Audio Analyzer
Operation Manual
(Firmware version 1.17)
3200 Sencore Drive, Sioux Falls, SD 57107
iii
TABLE OF CONTENTS
SAFETY PRECAUTIONS ...................................................................... inside front cover
DESCRIPTION................................................................................................................ 1
Introduction ............................................................................................................................1
Features.................................................................................................................................2
Specifications .........................................................................................................................4
Accessories............................................................................................................................6
I/O CONNECTIONS........................................................................................................ 7
Input Panel (Bottom when viewing display) .......................................................................7
Digital Input 1.....................................................................................................................7
Digital Input 2.....................................................................................................................7
Power Adapter Input Jack..................................................................................................7
Power Switch.....................................................................................................................7
Battery Compartment.........................................................................................................7
Output Panel (Top when viewing display) ..........................................................................8
Digital Audio Outputs .........................................................................................................8
Analog Audio Outputs........................................................................................................8
Word Clock In / Video Input ...............................................................................................8
DB-9 Connector.................................................................................................................8
LCD Contrast.....................................................................................................................8
Speaker.............................................................................................................................8
Battery Module Information .................................................................................................9
Battery Module Introduction ...............................................................................................9
Charging............................................................................................................................9
Automatic Power Switch ....................................................................................................9
Battery Life & Charging Times ...........................................................................................9
Clocks & Routing ...............................................................................................................10
Master Clock....................................................................................................................10
Output Clocking ...............................................................................................................10
USER INTERFACE....................................................................................................... 11
User Interface Features......................................................................................................11
Control Knob Operation ...................................................................................................11
Menus..............................................................................................................................11
Saving Preferred Settings................................................................................................12
Top Toolbar ........................................................................................................................12
Function Control and Information.....................................................................................12
Input Control and Information...........................................................................................12
Bottom Toolbar...................................................................................................................13
Analog Output Control .....................................................................................................13
Digital Output and Generator Control...............................................................................14
ANALYSIS FUNCTIONS MENU................................................................................... 16
Bitstream Analyzer ...............................................................................................................17
Digital Watchdog ..................................................................................................................20
Clock/Sample Counter..........................................................................................................22
Bitscope ...............................................................................................................................23
Distortion Meter....................................................................................................................25
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DIGITAL TESTS MENU................................................................................................ 27
Digital Lock Test...................................................................................................................28
Video Lock Test....................................................................................................................30
Transparency Test ...............................................................................................................32
Latency Test.........................................................................................................................34
Jitter Meter...........................................................................................................................36
SYSTEM TOOLS MENU............................................................................................... 38
Level Meter ..........................................................................................................................39
LAeq Dialog Level ................................................................................................................41
Signal Generator ..................................................................................................................42
Sweeps ................................................................................................................................44
Pass Mode ...........................................................................................................................47
UTILITIES MENU.......................................................................................................... 49
Digital Cable Tester..............................................................................................................50
Capture Sample Data...........................................................................................................51
Save Defaults.......................................................................................................................53
About....................................................................................................................................54
GLOSSARY .................................................................................................................. 55
WARRANTY & SERVICE INFORMATION............................................inside back cover
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DESCRIPTION
Introduction
The DigiPro Digital Audio Analyzer is a multi-function, dual-domain precision digital audio test instrument.
The DigiPro provides a powerful, complete set of test, troubleshooting and utility functions for digital audio analysis, in a hand-held DSP-powered device.
The DigiPro allows you to analyze any professional or consumer format stereo digital audio signal, and generate low-noise digital test signals, all at up to 24-bit/96k-sample rate resolution. Digital audio analysis features and functionality, normally found only on expensive bench test equipment, are now available in a portable, easy-to-use and cost-effective package.
The DigiPro features a Transparency Test, Bit-Stream Analyzer, Lock Test, Bit-Scope, Latency Test, Digital Watchdog, Jitter Meter, Clock/Sample Counter, Distortion Meter, and more!
The DigiPro provides all the connections you’ll need; two sets of AES/EBU and SP/DIF inputs, including Toslink and ADAT, plus Word Clock in. Digital outputs include AES/EBU, SP/DIF, and Toslink/ADAT, and Word Clock out. Analog stereo headphone and unbalanced mono analog outputs provide for testing of dual-domain devices, such as analog to digital converters (ADCs) or digital mixing consoles. Also included are ADAT sync and RS-232 serial for computer interfacing.
Multi-Tasking
The DigiPro has independent input, output, and monitor sections. This allows simultaneous analysis, signal generation, and analog headphone monitor.
Multi-Function
The DigiPro Digital Audio Analyzer employs a powerful DSP engine. All functions, filters, and processing are implemented in DSP firmware algorithms. As each function is loaded into internal memory and executed, the DigiPro takes on a completely new personality.
Precision Test & Measurement
The DA795 DigiPro digital analyzing and generator functions, with digital inputs, digital outputs, and analog outputs, provide an integrated level of dual-domain test and troubleshooting efficiency that smple digital monitoring devices can’t begin to offer. This allows you to easily test digital signal integrity , check for digital equipment compatibility, and check for status information that doesn’t match the audio data.
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Features
Bitstream Analyzer- Totally analyzes digital audio stream characteristics, checking header
status bytes, plus actual word length and sample rate, bit activity, and low voltage.
Digital Watchdog - Captures signal errors for a test period and graphs the errors.
Clock / Sample Counter - Measures the actual digital sample rate, word clock, and superclock
frequencies for a digital audio signal.
Bitscope - Shows distortion, noise or jitter on an S/D or X-Y scope, and also applies the results
to the internal speaker, headphones, and line output.
Distortion Meter - Measures THD+N (Total Harmonic Distortion & Noise)
Digital Lock Test - Tests whether a digital audio input (AES/EBU or S/PDIF format) is locked
to another digital audio input, word clock, superclock, ADAT input, or ADAT sync (to <1ppm).
Video Lock Test – Tests whether a digital audio signal in AES/EBU, S/PDIF, or ADAT format
is locked (to <1ppm) with a video sync signal (black burst).
Transparency Test - Verifies that a device passes digital test waveforms without errors, using
either synchronous or asynchronous test. Any modification of the digital data stream will be detected.
Latency Test - Checks the amount of signal delay through a device with a digital device input,
and either a digital or analog device output.
Jitter Meter - Tests RMS interface jitter on a digital signal (to 150ps) or clock (to 35ps), as
referenced to an internal crystal or external master clock.
Level Meter - Monitors the level of a digital source signal. Numeric, VU (volume units), and
PPM (peak program meter) meters are available.
LAeq Dialog Level - LAeq refers to the "equivalent" average sound level, measured using A-
weighting which is most sensitive to speech intelligibility frequencies of the human ear. LAeq is prescribed in the AC-3 DTV audio standard as the proper means to set the "dialnorm" value, which sets the volume of dialog in every consumer DTV receiver.
Signal Generator - Creates standard digital audio test signals with sine, square, white, and pink
waveforms.
Sweeps – Provides both amplitude and sine sweep modes. Amplitude sweep generates a swept sine wave, outputs it to both the analog and digital outputs,
and measures the incoming digital audio signal level. Results are plotted on the screen.
Sine sweep generates a swept sine wave, between two selected end frequencies, and repeats the
sweep until turned off.
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Pass Mode – Passes a digital input signal through to the output with any selected modifications.
Possible signal modifications include changing header information, performing sample-rate conversion (from 44.1 kHz to 96 kHz), changing signal formats (AES/SPDIF/ADAT), adding digital gain or attenuating the signal.
Digital Cable Tester - Tests digital audio cables for functional quality. Provides a method of
comparing digital audio cables.
Capture Sample Data - Captures a buffer of data from the AES or SP/DIF input, and then
allows you to step through the buffer to examine the data, or search for particular values.
Digital Monitor - Allows you to hear a digital signal with headphones or built-in speaker.
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Specifications
Digital Input/Output
Digital Signal Formats
AES-3 S/PDIF coaxial S/PDIF optical (Toslink) ADAT BNC
Lock Detect
Lock detect: <1 ppm.
Digital Watchdog
Minimum Test Period: 1 minute Maximum Test Period: 24 hours Minimum length of detected error, all test times: 1 sample
Transparency Test
Maximum number of errors per channel: 65,536. Maximum length of test: unlimited.
Frequency Counter
Signal Generator
Latency Test
Jitter Meter
Analog Output
Frequency Accuracy: 0.1 ppm, or ±0.01 Hz in a word clock or sample clock, or ±4 Hz in a master clock signal (256xFs).
Sine wave output frequency: 1 Hz to 20 kHz Sine wave distortion: Better than –130 dB THD+N
Accuracy: ±2 samples
Jitter Range
AES/EBU or S/PDIF Input: 150 ps to 100 ns Clock/Super clock Input: 35 ps to 100 ns
Jitter Accuracy: greater of ±5% of reading or ±10ps
Output voltage range:
Unbalanced: 0 dBu to –66 dBu
Balanced: +6 dBu to –60 dBu Output voltage accuracy: ±1 dB Sine wave distortion: Better than –85 dB THD+N
Standards
AES-3 VU/PPM: DIN 45406 (IEC 60268)
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General/Environmental
Input Impedances
XLR digital inputs: 110 kohms, nominal S/PDIF digital inputs: 75 kohms, nominal BNC Word Clock/Video input: 75 kohms, nominal
Output Impedances
XLR digital output: 110 ohms, nominal S/PDIF digital output: 75 ohms, nominal Word Clock digital output: 75 ohms, nominal ¼” Stereo Headphone analog output: 5 ohms, nominal RCA phono unbalanced analog output: 110 ohms, nominal
Display: 64x128 pixel blue LCD with backlight Size: 5 1/2" x 12 1/2" x 2 1/4" (HWD) Weight: 4.5 lbs.
Temperature Range
5°C to 45°C, non-condensing
Power
Battery: Sealed Lead Acid 6 Vdc module. AC adapter/charger: 100-240 Vac, 47-63 Hz, 7.5 Vdc, 4 A
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Accessories
DA795 Digital Audio Analyzer Accessories
Sencore Part #s
13G122
13G124
17G46
60G81
Description Photo
XLR Audio Cable – a 12 ft. microphone cable for interfacing balanced audio inputs and outputs to the DA795.
supplied
Serial Interface Adapter Cable – a
6’ computer serial interface adapter cable (straight through), connects between the unit’s RS232 jack and a computer serial port.
supplied
Sealed Lead Acid Battery Module
– 6 volts
supplied
AC Power Adapter/ Charger 7.5
VDC, 4A - plugs into the DA795 to charge the battery or to provide AC operation.
supplied
Battery not pictured
Soft Carry Case padded carrying case to transport unit; includes extra
10B897
storage capacity for supplied accessories.
supplied
http://www.sencore.com mailto:sales@sencore.com 1.800.736.2673
Specifications and accessories subject to change without notice.
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I/O Connections
Input Panel
(Bottom – when viewing display)
Digital Input 1
Digital Input 1 connectors include an AES/EBU input, the S/PDIF input, and an optical input connector, which supports both ADAT and S/PDIF (Toslink) format. These inputs are selectable within most DigiPro functions. Note that the S/PDIF and Toslink inputs share circuitry, so only one of the inputs should be used at a time.
Digital Input 2
Digital Input 2 connectors include one AES/EBU input and one S/PDIF input. These inputs are selectable within the Digital Lock Test, Jitter Meter, and the Digital Cable Tester functions. The actual digital audio data is not decoded from these inputs. The Digital Input 2 signal is used only for timing, jitter, and lock measurements.
Power Adapter Input Jack
The power input powers the DigiPro and charges the battery when the DigiPro is switched off. Using an incorrect power adapter can damage the battery, battery charger, and/or the DigiPro. The Digital Audio Analyzer requires 7.5 Vdc unregulated at a minimum of 800ma. The input connector is a 2.1mm coaxial power connector, positive on the center pin.
Power Switch
The power switch is mounted on the DigiPro input panel, and switches the DigiPro on or off when it is powered by the internal battery or the AC power adapter.
Battery Compartment
The Digital Audio Analyzer includes an internal rechargeable sealed lead acid (SLA) battery. The battery can be accessed by unscrewing the thumbscrew and opening the battery compartment door on the front of the unit. The battery is removable by sliding the battery module out of the DigiPro and disconnecting the circuit board.
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Output Panel (Top – when viewing display)
Digital Audio Outputs
Digital output connectors include an AES/EBU output, S/PDIF coaxial output, ADAT/Toslink optical output, and a Word Clock Output. The ADAT output sends out a copy of the stereo digital audio data on all four ADAT stereo pairs. The Word Clock output is derived from the output digital audio transmitter, and so follows the lock source selected for the generator.
Analog Audio Outputs
Analog output connectors include an unbalanced RCA phono output and a 1/4” TRS (tip, ring, sleeve) output that can be configured as a stereo output (suitable for headphones) or as a balanced mono output. The analog outputs monitor the digital input, or provide an analog copy of the digital output. (See the Top Toolbar section of this manual.)
Word Clock In / Video Input
The Word Clock In (BNC connector) is used to lock the DA795 to an external clock, and also as an input to the jitter/lock tester board, as a 256xFs sample clock. The DigiPro digital output can be locked to this source, if desired. Also, this connector can be selected by the Clock/Sample Counter function, to measure the frequency of the signal. This connector also functions as a video input for the Video Lock Test function, for testing lock between a video sync signal (black burst or other video signal) and an AES, S/PDIF, Toslink, or ADAT digital audio signal.
DB-9 Connector
This connector is used both as a serial RS-232 interface port and as an ADAT sync input port. The ADAT sync signal is a word clock signal on pin 8 of this connector, and does not interfere with RS-232 communications, which uses pins 2, 3, and 5 on the DA795. The ADAT Sync input and the Word Clock Input share circuitry, so only one of these inputs should be used at a time.
LCD Contrast
Use this control to adjust the contrast of the blue super-twist LCD display for optimum viewing.
Speaker
The speaker outputs a mixed left and right channel audio that can be switched on or off independently of the analog line outputs. However, if the main analog output is switched off, the speaker audio is also off. The internal speaker may be used for monitoring digital signals when headphones are not available or convenient.
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Battery Module Information
Battery Module Introduction
The battery module consists of a battery with a battery charger board mounted directly on the battery. It has two coaxial power connectors mounted on it, one that accepts the AC power adapter plug, and one that mates with the DigiPro internally. These connectors are different sizes so that the power plug cannot be plugged into the wrong connector. Also, the battery module cannot be inserted the wrong way.
Charging
Anytime the AC power adapter is plugged into the battery module, the battery will be charging. You cannot overcharge the battery. It is best to leave the AC power adapter plugged into the battery module whenever possible. When the battery is mounted in the DigiPro, and the DigiPro is switched on, the battery charges very slowly, since most of the power from the AC power adapter is being used to run the DigiPro. You can charge the battery either in the DigiPro, or with the battery module removed. If you have a spare battery module, you can charge one battery module with the AC power adapter while you operate the DigiPro with the other, charged, battery module.
Automatic Power Switch
The battery module uses an automatic relay to switch from AC to battery power, and to prevent the SLA battery from being completely discharged, which can damage it. The switchover happens automatically as the AC power adapter is plugged into the battery module. In some cases, it is possible to latch the relay into a state in which the battery, even though it is charged, will not operate the DigiPro. These conditions include plugging the AC power adapter into the battery module with no or very low AC power present, and extreme physical shock. To correct this condit io n, just remove the AC power adapter plug from the battery module, make sure the AC power adapter is getting good power, and plug it back into the battery module.
Battery Life & Charging Times
The display backlight is always on, since the blue LCD is not visible without the backlight.
Battery Life Charge Time DA795 On 1.1 hours 7.0 hours DA795 Off (or battery removed) 3.0 hours
Warning: Storing the DigiPro for long periods of time with a discharged battery can shorten the life of the battery, or possibly destroy the battery. The battery should be kept charged at all times, and cannot be overcharged, so it is best to leave it the power adapter plugged into the battery connector when the DigiPro is not in use.
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Clocks & Signal Routing
Digital audio equipment locks an oscillator to an incoming digital audio signal, clock, super­clock or sync signal. The DA795’s internal receiver (Master Oscillator) may be locked to an internal clock (a crystal), or an external input signal which can come from various input signal sources. Input sources include a word clock, an AES or S/PDIF signal, an ADAT sync signal, or from a super clock signal. This provides maximum versatility when analyzing digital audio signals with the DA795.
Master Clock
The DA795’s Master Clock is an internal clock that runs at 256 or 512 times the sample rate (word clock). It is used to clock the digital output and the internal analog-to-digital converter (ADC). The possible locking sources for the Master Clock are:
x Internal 32 kHz crystal
x Internal 44.1/88.2 kHz crystal
x Internal 48k/96 kHz crystal
x Recovered master clock from the digital input receiver
x External word clock, after running through the PLL at 256 times the sample rate
x ADAT recovered clock from the ADAT receiver circuit.
x ADAT Sync, after running through the PLL at 256 times the sample rate
None of the ADC derived features of the DA795 are available when the Master Clock is not locked. These include the battery level/AC indicator, Digital Lock Test, Video Lock Test, Jitter Meter, Level Meter, and the Digital Cable Tester. The Master Clock lock source is selected at the right end of the Bottom Toolbar. The frequency of this clock is always being counted, and if it is running at a frequency that is too slow to be considered valid, the locking source selection field will blink. A valid Master Clock can always be obtained by selecting any of the DA795’s internal crystals such as “Int 48 k” as indicated in the bottom right toolbar field.
Output Clocking
The DA795 can operate in one of two output modes: (1) Generator output mode or (2) Pass­through mode. In a generator mode, the internal generator creates a test signal and sends it to the digital output. In a pass-through mode (Pass Mode function only), the DA795 sends the input signal to the output, possibly with modifications. In either case, you need to select a valid lock source for the digital output, using the Bottom Toolbar.
There are times when may you want to re-clock a digital signal to match a different sample rate. The Sample Rate Converter (SRC) in the DigiPro Pass Mode function can convert an input signal at any supported sample rate (32 kHz to 96 kHz) to an output signal at any other supported sample rate (32 kHz to 96 kHz).
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User Interface
User Interface Features
The DA795 has many functions, features, and options. To make it easier to use the functions, commonly used control fields are located in the Top Toolbar and Bottom Toolbar, and are the same on most screens. Once you learn how to operate one function, you will have an easier time using the next one. The following sections discuss common user interface features.
Control Knob Operation
The Control Knob is used like a mouse on a computer. It provides a means of navigating the screens, selecting values, and changing the contents of control fields. To move around the menus, or the fields in a function, just turn the Control Knob clockwise or counterclockwise. The moves the control focus (highlight) around the screen. With the focus on a menu item or control field, clicking the Control Knob does one of three things:
1. Selects the choice (as on a menu)
2. Changes the option in a control field (if there are only a few choices, like on and off)
3. “Locks” the cursor to allow you to turn the Control Knob and change the value of a control field. Turning the Control Knob clockwise increases the value, counterclockwise decreases the value.
Figure 1
Menus
When you initially power up the DA795, after the initialization screen you will see the main menu screen. It has four menu items (Fig. 1). Clicking on one of these menu items displays a second menu which includes a list of named functions. Clicking on one of these function names starts the selected function. To exit a function, or to move from a function list to the main menu, just click on the Back character (< ) in the upper left corner (Fig. 2).
Figure 2
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Saving Preferred Settings
Many DA795 functions have control fields that you might want to have default to the same setting every time you turn the unit on. The following control fields can have their current setting saved as their default value: digital input source, sub-menu choices on all of the functions, and generator settings, including lock source, word length, frequency, and level. To store the current settings so that the DA795 will start up next time set this way, set up the DA795 the way that you want it, go to the Setup & Calibration function on the Utilities menu, and select “Save” on the Save Defaults screen. The next time you power up the DA795, your selections will be restored as the default settings.
Top Toolbar
The top line on every function screen has control fields that are used to identify and control the function and select inputs.
Function Control and Information Input Control and Information
Exit Arro
Battery Indicator Screen Title
Function Name
Input Lock
Input Select
Input Sample Rate
Input Level Meter
Function Control and Information
These items are on the left side of the Top Toolbar. x Exit Arrow. The exit arrow in the upper left corner of the screen exits the function and returns
you to the menus when you click on it. (see Figure 2)
x Battery Indicator. This field shows the relative battery level, or remaining charge in the
battery, when operating on the internal battery. When operating with the AC power adapter, this field shows the AC power symbol.
x Function Name. The name of the function currently running is shown in a box. The control
focus cannot highlight this field.
x Screen Title. Some functions have more than one function screen available. This field will
display the title for the active function screen. If you can move the control focus to highlight this field, you can click here to select the other screens.
Input Control and Information
These items are on the right side of the Top Toolbar. They are shown for all functions that use Digital Input 1 for the input signal source.
x Input Lock. The lock icon (padlock) will be open (unlocked) if no input lock is detected, or
closed (locked) if input lock is detected for the currently selected input. Clicking on this lock icon will take you to the Bitstream Analyzer screen, to get more information about the input signal.
x Input Select. The Digital Lock Test, Jitter Meter, and the Digital Cable Tester functions
receive input from Digital Input 2. For the other functions, the sources will be from Digital Input 1: AES, SPDIF/Toslink, or any of the four ADAT pairs. If you select SPDIF/Toslink, be sure that only one of those inputs is connected at a time, to prevent conflicts.
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x Input Sample Rate. This field displays the measured sample rate of the digital input signal,
with a resolution of 0.1 kHz. Note that this is the actual running sample rate, not just a reporting of the signal status bytes. This sample rate is computed by the digital receiver circuit DSP, so if the sample rate converter is running, you will see the letters “SRC” rather than a frequency. This is because the incoming frequency is being sample-rate converted within the receiver circuit, before the DSP; thus, the incoming frequency is not known to the DSP. If no valid digital input signal is detected, this field indicates “n/a.”
x Input Level Meter. The far right end of the Top Toolbar displays the digital level of the input
signal, with a 7-segment bar graph. The bar graph consists of two vertical lines, for the left and right channel levels. Each dot represents approximately 6 dB. When all seven segments are lighted, the digital input level is 0 dB FS.
Bottom Toolbar
The bottom line on every function screen has control fields that are used to control the analog outputs and the digital generator (The Latency Test doesn’t need nor display all of the Toolbar controls).
Analog Output Control Digital Output and Generator Control
Analog Output Control
The control fields for the analog output section are on the left side of the Bottom Toolbar.
x Output Type. This control field changes the 1/4” Headphone connector from
a stereo headphone output to a balanced mono output. Select Headphone to use the Toolbox as a high-quality analog headphone amplifier with integral DAC. Select Balanced (XLR) when you need a balanced analog output, for example for a generator output.
x Analog On/Off. The 1/0 icon switches all the analog audio outputs on or off
(including the speaker).
x Analog Output Level. This level gauge icon controls the analog output level.
Every rotating click of the Control Knob changes the output level by approximately 1 dB.
x Speaker On/Off. This field switches only the speaker on or off. The speaker
has its own amplifier, and can be switched off independently from the other analog outputs. To enable the speaker output, both the Analog On/Off and the Speaker On/Off fields must be switched on.
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x Analog Output Source. This field switches between Monitor and Generator for
the analog output. M selects the digital input for monitoring; G selects the internal generator (or whatever digital output signal is present). Switching from Monitor to Generator changes the source data for the DAC from the input
digital receiver circuit to the output digital transmitter. Therefore, in Monitor mode you will hear exactly what is being received, as selected by the input select field on the top toolbar, and in Generator mode, an exact copy of the digital output signal will be routed to the DAC. In either case, a valid clock source is required. For example, if G is selected, and the output clock select is flashing, there will be no analog output. Likewise, if M is selected, a valid input signal is required.
Headphone Warning: Be careful when wearing headphones and changing sample rates, analog monitor source, or input connections. Although the analog output is muted in most situations that may cause high analog levels, it is not always possible. We recommend that you remove headphones before switching any clocks, or changing functions, until a stable clock and lock has been established, and the DigiPro has had a chance to regain control of the analog outputs.
Digital Output and Generator Control
The control fields for the digital output and generator are on the right side of the Bottom Toolbar. Some fields control only the digital generator, while other fields control aspects of the digital output, whether the output source is the generator or another source, such as a digital input.
x Generator Jump. The sine icon jumps to the Generator function
screen for more output control options, such as frequency and waveform selection.
x Digital On/Off. The 1/0 icon switches the digital audio outputs on or
off.
x Digital Output Level. This level gauge icon controls the digital
generator output level. Every rotating click of the Control Knob changes the output level by exactly 1 dB.
x Word Length. This number field controls the word length (bit depth)
of the digital output. You can select any word length from 8 to 24 bits.
x Output Lock Source. This control field selects the lock source
(master clock) used for the digital output. You can select any of the five internal crystals (32 kHz to 96 kHz), the Word Clock input, the AES or S/PDIF input, the ADAT optical input, or the Super clock. The
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ADAT sync connector (pin 8 of the DB-9 connector) and the Word Clock BNC input share the same input line. To use the ADAT sync connector (DB-9 connector, pin 8), select the Word Clock input and remove any connectors from it. Likewise, when using the Word Clock input, do not connect an ADAT sync connector. Note that if you select a lock source with no input signal, there will be no digital output. In this case, the Lock Source select field will blink. Also, since the ADC is driven by the output clock, the Battery Indicator, Jitter Meter function, and Input Level Meter will not function.
x Lightpipe Format. The A/T icon selects the output format for the optical output
connector. A selects ADAT format; T selects Toslink. Note that in ADAT format, the digital stereo output signal is copied to all four sets of ADAT stereo pairs.
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ANALYSIS FUNCTIONS
The Analysis Functions menu contains functions that are useful in analyzing digital audio signals. The standard input source is Digital Input 1. The Analysis Functions menu includes the following functions:
Bitstream Analyzer Digital Watchdog Clock/Sample Counter BitScope Distortion Meter
The Analysis Functions menu, showing the available test functions.
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Bitstream Analyzer
Description
The Bitstream Analyzer displays a complete analysis of a digital audio signal, including the digital signal type, sample rate, word length, carrier amplitude, digital audio level, bit activity, and digital receiver integrity analysis. The Bitstream Analyzer displays both reported channel status information and
Bitstream Analyzer Applications
x Any time you need to know what’s going on in a digital wire, plug it into the Bitstream
Analyzer.
x Check actual word length (compared to reported or claimed word length), actual running
sample rate, signal voltage, or channel status information.
Bitstream Analyzer Display/Controls
Top Toolbar. The Top Toolbar provides control fields that allow you to switch between the
Status screen and the Detail screen; select the Digital Input 1 connector you wish to use; and see a low resolution measurement of the sample rate of the selected digital input signal (to 0.1 kHz).
actual digital data to allow you to detect status errors. Being able to view a complete set of channel data allows you to quickly remedy digital interface problems that would otherwise put your digital system entirely out of service or cause poor quality operation.
Status Screen. The Status Screen provides information on many aspects of a digital audio signal, including signal voltage, actual sample rate, channel status information, digital audio levels, bit depth and bit activity. Click on the “Status” title to switch to the Detail screen.
Top Toolbar
Channel Status
Confidence
Indicators
Bit Activity
Bottom Toolbar
Channel Status
Signal Voltage
Sample Rate Counter
Audio Level
Word Length
o Channel Status. The second line on the screen displays the information translated from the
input channel status data. Channel Status can be thought of as a “header” that contains information about the digital audio stream. It is set by the device creating, or transmitting, the digital audio. In some cases, discrepancies between the reported channel status information and the actual digital audio stream can cause problems with devices that are receiving and trying to decode the digital audio. Receivers use channel status information to configure themselves automatically to decode a received bit stream. Discrepancies can cause intermittent or no receiver operation.
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Field 1: Status Use. (Pro/Con) AES3 connections generally send professional data.
SPDIF and Toslink connections generally send consumer data. This bit determines how other channel status information is interpreted.
Professional:
Field 2: Sample Rate. 32 kHz; 44.1 kHz; 48 kHz; not indicated (---) Field 3: Word Length. 16 to 24 bits; not indicated (---) Field 4: Channel Mode. 2ch; 1ch; not indicated (---) Field 5: Emphasis. CCITT J.17; 50/15 us; no pre-emphasis; not indicated (---)Field 6: Validity. PCM Audio; No PCM (V) Field 7: Fs Down Scaling. No scaling; Scale indicated sample rate by 1/1.001
Consumer:
Field 2: Sample Rate. 32 kHz; 44.1 kHz; 48 kHz; not indicated (---) Field 3: Word Length. 16 to 24 bits; not indicated (---) Field 4: Category Code. Code indicates equipment type. Field 5: Emphasis. 50/15 us; no pre-emphasis; not indicated (---)Field 6: Validity. PCM Audio; No PCM (V) Field 7: Copy Bit (SCMS). Copyright asserted; No copyright asserted
o Confidence Indicators. Starting on the third line, to the left, is a box of “confidence
indicators” that should all have check marks. These confidence indicators are received from the digital receiver circuit; signal voltage check (Vpp), eye pattern pass/fail (Eye), left channel bit presence (BitsL), right channel bit presence (BitsR), biphase status (BIP), cyclic redundancy check (CRC), sample rate check (SR), and parity check (Par). Any X’s that are shown could be cause for concern and should be investigated.
o Signal Voltage. On the third line, to the right, is a peak-to-peak volt meter, with indicator
marks at the recommended max and min voltage levels for either an AES or S/PDIF digital signal. Note that, if you connect an optical cable, the voltage will always read 0.
o Validity Bit. Every frame of digital audio has a Validity bit that may be set to indicate
that the data stream is not “normal” digital audio (PCM), and therefore should not be decoded. Examples of this are Dolby Digital (AC-3) or MPEG data. These data streams use the normal digital audio bitstream as a carrier, but are sending packed bursts of data that must be decoded using a particular algorithm, known as a codec. If the Validity bit is set (indicating non-PCM audio), a letter “V” appears to the left of the signal voltage meter.
o Sample Rate Counter. On the fourth line, to the right, is a sample rate counter that
displays the precise running sample rate of the digital audio frames.
o Audio Level ( dB FS). This horizontal graph shows the audio level of the digital input
signal, referenced to full scale output. 0 dB FS equals the highest audio level (digital number) that the employed word length is capable of representing.
o Bit Activity. This displays the bits that are changing, by alternating between a ‘+’ and a
‘-.‘Any non-changing (stuck) bits are shown as their actual value (0 or 1).
o Word Length. These two fields, at the right end of the Bit Activity display, show the
word length of the left and right channels of the incoming digital audio, computed from actual changing bits. Note that if there is no incoming signal, or if the signal is “digital black,” the word length is not computed.
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Detail Screen. The Detail screen provides a detailed view of the channel status bytes. Click on the “Status” title to switch to the Detail screen. Click on the title “Detail” to switch back to the Status screen.
Channel Status
Validity Bit
Channel Status
Bytes
Channel Status
Bytes
Channel Status
o Status Information (Ch A). The second line on the screen displays the channel status
information, translated from the channel A (left) input channel status data.
o Validity Bit. If the Validity bit is set (indicating non-PCM audio), the letter “V” appears
on the left end of the third line, just below the channel status information.
o Channel Status Bytes. All 24 channel status bytes for both channels (A and B) are
displayed, starting on the fourth line on the screen. These byte values are all shown in hex format.
Bitstream Analyzer Operation
x Connect and select the input signal. Connect a digital signal to one of the Digital Input 1
connectors; AES/EBU, S/PDIF/Toslink, or ADAT. Select this input on the Top Toolbar.
x Select a Lock source in the Bottom Toolbar. Hint: Select “Int 48k” for most input signal
analyzing measurements.
x Confirm Lock: A lock symbol should be shown in the top center if it is locked to an
incoming signal.
x Read the display results.
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Digital Watchdog
Description
The Digital Watchdog monitors a digital signal over an extended time period to detect errors or level overloads. It will run up to 24 hours, and will find as little as one sample error in 24 hours.
Any selected test length period is divided into 120 data periods, so time resolution depends on the test length. Although all errors are logged, errors are combined for reporting within each data period.
Digital Watchdog Applications
x Locate intermittent faults in equipment and cabling. x Monitor digital levels for conformity to level restrictions.
Digital Watchdog Display/Controls
For example, if you set the test length to 2 hours (120 minutes), at the end of each minute, if any errors have occurred in that minute, a new error bar will be drawn on the screen. If there were no errors, the screen will stay blank for that data period. Then, you can come back later and pinpoint any error to the closest minute.
Level Threshold
Error Bars
Cursor Time Test Length
Error Codes
Progress Bar
Cursor
# of Errors
o Level Threshold. You can select a level that, if exceeded, triggers a Signal Over error (Ov).
Or, leave it set to 0.0 dBFS to look for Digital Overs (defined here as four or more consecutive samples of full signal value).
o Cursor Time. Displays the time placement of the cursor, relative to the starting time of the
test.
o Test Length. Set the test duration time using the time field in the lower right corner. Choose
from 1 min, 5 min, 10 min, 15 min, 1 hr, 2 hrs, 8 hrs, or 24 hrs.
o Progress Bar. A horizontal bar runs over the top of the error graph to indicate the relative
period of time tested, compared to the Test Time.
o Error Bars. Any errors that are detected within the test time produce a vertical bar on the
screen. The more errors detected within that data period, the taller the bar. You can place the control cursor over any error bar to display the error code(s) for that data period.
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o # of Errors. The total number of errors within the data period selected by the cursor is
displayed here.
o Error Codes. The error codes are displayed when the cursor is placed over any data period
that displays an error bar. Following are the possible error codes:
CR – CRC error. The digital receiver has found a CRC (data integrity) error. This usually indicates a serious problem with the signal or transmitter. Check cabling. Lk – Lock error. Lock has been lost. Usually many other errors will be reported if lock is lost. If this error is occurring intermittently, it may indicate connection problems or non­locked signals.
V – Validity flag. Ey – Eye error. The digital receiver chip has determined that the incoming signal does not
meet minimum eye pattern criteria. The eye pattern is used to check that the digital audio waveform is high enough (has enough voltage difference between high and low states) and is wide enough (rise and fall times are not too slow). This pattern looks like an eye when viewed on a high-speed digital oscilloscope. Although we do not show this pattern, the digital receiver in the DigiPro detects waveforms that are on the verge of eye pattern problems. Eye pattern errors may indicate a cable problem, such as poor cable quality (high capacitance will lower rise and fall times) or excessive cable length, which can reduce signal voltage level. Bp – Biphase error. Digital signals are biphase encoded. This way, the overall signal has no offset – it averages to 0 volts. If the biphase encoding is not done correctly, this error will be detected. You should never see this error in normal operation. Pr – Parity error. The digital receiver circuit has determined that the incoming signal has a parity error. Ov – Signal over. This error will be triggered if the set dB level is exceeded, for even one sample. If the trigger level is 0.0 dBFS, the error will be triggered if more than four consecutive samples are detected at full signal level.
Digital Watchdog Operation
x Connect and select the input signal. Connect a digital signal to one of the Digital Input 1
connectors; AES/EBU, S/PDIF/Toslink, or ADAT. Select this input on the Top Toolbar.
x Select the test conditions. Select the desired test length and possibly a level threshold.
x Run the test. Click the Run icon to start the test.
x View the results. Check whether any errors occur within the test period (an “X” will appear in
the center of the Top Toolbar). Place the cursor over any error bars to check when the error occurred, and view the associated error codes.
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Clock/Sample Counter
Description
The Clock/Sample Counter accurately measures incoming sample rates (FS) of digital signals, as well as bit clock, word
Clock/Sample Counter Applications
x Identify word clock signals.These signals generally exist on coaxial cables with BNC
connectors. You can see the actual clock rate in MHz.
x Accurately measure sample rates of digital signals. x Identify equipment that is not running at the correct sample rate, or that requires a sample rate
converter.
Clock/Sample Counter Display/Controls
clock (Fs) and video frame frequencies. For bit clocks and word clocks, the corresponding sample rate is also computed.
Input Select
Clock Frequency
Sample Rate
Frequency Error
o Input Select. Select the input signal you wish to count.
o Clock Frequency. Displays the word clock or super clock frequency.
o Sample Rate. Displays the sample rate of a digital audio signal, or the frame rate of a
composite video signal (black burst).
o Frequency Error. The sample rate of the input signal is compared to the selected internal
clock signal and the frequency error is expressed in parts per million (ppm).
Clock/Sample Counter Operation
x Connect and select the input signal. Connect a digital signal to one of the Digital Input 1
connectors; AES/EBU, S/PDIF/Toslink, or ADAT. Or, if desired, connect a word clock, bit clock or composite video signal to the BNC Word Clock In connector. Select the input that you are using in the Input Select field.
x Read the results. The measured clock rate, sample rate/frame rate, and error are displayed.
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BitScope
Description
The BitScope displays a decoded digital audio signal in the time domain, on an oscilloscope­like screen. Auto trigger makes it easy to view the audio waveform for troubleshooting
BitScope Applications
x Look for audio signal distortion. x Increase the signal gain (lower dB FS vertical range) to listen to dither, or a signal below the
dither threshold.
x Increase the signal gain, with no audio signal, to listen for converter noise. x View dither and converter noise with high digital gain applied. x Align equipment phase delays. x View the program phase content (stereo separation) in X-Y mode.
BitScope Display/Controls
S/D Mode (Samples/Division). This mode allows you to view the decoded audio signal on a
standard oscilloscope type display. Changes in the amplitude of the audio signal are plotted along the vertical axis. Changes in the audio signal over time are plotted along the horizontal axis. To view the phase relationship between left and right channel audio signals, click on the “S/D” title to switch to the X-Y Mode screen.
purposes. Two channels of a digital audio signal can also be compared, in the X-Y mode, to view the phase relationship between the channels of audio.
Channel Select
OVER
Vertical Range Time Scale
o Channel Select. You can choose to view either the left or right channel audio signal. To
view the phase relationship between left and right channels, select the X-Y Mode screen.
o OVER. Indicates when the digital signal exceeds the dB FS level selected in the Vertical
Range field. This is often desired, as when “zooming” into a digital signal, to see or hear distortion, converter noise, or dither noise.
o Vertical Range. This field selects the level of digital signal that will fill the screen from top
to bottom. When the vertical range is set to 0 dB FS, a 0 dB FS digital audio signal will fill the screen from top to bottom. A lower level signal will be occupy less of the screen. Setting this field to –6 dB FS applies 6 dB of gain (1 bit), and any signal that appears full screen is
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actually at –6 dB FS. By setting this field to a lower negative number, you can zoom into the digital signal, essentially applying gain to the input. You can reduce this number to -120 dB FS, applying 120 dB of digital gain.
o Time Scale. You can set the time scale as fine as 2.5 samples per division, or as coarse as
250 samples per division. Choose whatever time scale provides the best picture.
X-Y mode. You can select X-Y mode to view the incoming stereo signal on a phase scope. Signals that are in phase will show up as a diagonal line pointing to the 0 mark on the screen (upper right). If the phase of the two signals shifts, approaching 90 degrees, the line will open to an oval, pointing up. Further phase shift will close the oval back to a single line, pointing to the 180 mark on the screen (upper left).
As the phase angle increases, approaching 270 degrees, the line will again open to an oval, pointing down. Since an oval is symmetrical, pointing up and pointing down looks the same. Therefore, you cannot distinguish between 90 degrees and 270 degrees, but nonetheless, the absolute phase relative to 0 degrees appears clearly. The Vertical Range field, described above, can be used to magnify the signal on the screen.
Click on the “S/D” title to switch to the X-Y screen. Click on the title “X-Y” to switch back to the S/D screen.
Channel Select
Vertical Range
BitScope Operation
x Connect and select the input signal. Connect a digital signal to one of the Digital Input 1
connectors; AES/EBU, S/PDIF/Toslink, or ADAT. Select this input on the Top Toolbar.
x Run the test. Make sure the Run/Pause icon is set to Run. (Pause is used for freezing results).
x View & hear the results. The decoded digital audio waveform will be shown on the screen.
Any digital gain applied with the Vertical Range control is also applied to the analog monitor, so you can listen to amplified signal, either through the internal speaker, headphones, or via the line output. Any signal exceeding the screen upper and lower limits will cause the “OVER” indicator to appear.
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Distortion Meter
Description
The Distortion Meter measures the total harmonic distortion plus noise (THD+N) of a digital audio signal. A narrow digital notch filter eliminates the fundamental frequency from one channel of a digital input. The result ing filtered RMS signal level is compared to the unfiltered RMS signal level to determine the dB and percent THD+N.
Distortion Meter Applications
x Measure the distortion from an analog-to-digital converter (ADC). The distortion of the
DA795 analog sine wave generator output is near –90 dB, so any distortion measured above that level is coming from the ADC.
x Measure the distortion from a sample rate converter (SRC). Sample rate converters are
usually implemented using digital filters, which can cause distortion.
x Measure the distortion from any digital device which modifies the signal without changing
the frequency or waveform content. For example, an ADC/DAC pair, or the busses in a DAW can be tested.
The Distortion Meter can measure distortion down to about -118 dB (the distortion in the DA795 digital sine wave generator is near the theoretical minimum of -145 dB), so any distortion above about -118 dB is coming from the DUT. The measured THD+N is shown two ways: as a percent of the input signal magnitude, and as an absolute dB level, referenced to 0 dB FS.
Distortion Meter Display/Controls
Test Frequency
dB Distortion
Distortion Scale
o Test Frequency. The distortion test can be run at several frequencies, starting at 63 Hz and
increasing in octave steps: 63 Hz, 125 Hz, 250 Hz, 500 Hz, 1000 Hz, 2000 Hz, and 4000 Hz. The signal generator source needs to be set to the same audio frequency.
o Channel Select. Selects whether the test is performed on the left channel or right channel
digital audio signal.
o dB Distortion. Displays the distortion level, referenced to 0 dB FS.
o % Distortion. Displays the distortion level, as a percentage of the input signal magnitude.
Channel Select
% Distortion
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o Distortion Scale. Displays the percentage distortion with a pointer on a linear distortion bar
scale. The midpoint marks are half the value of the marked points to their left (50, 5, 0.5, etc.).
Distortion Meter Operation
x Connect and select the input signal. Connect a digital signal from the device under test
(DUT) to one of the Digital Input 1 connectors; AES/EBU, S/PDIF/Toslink, or ADAT. Select this input on the Top Toolbar.
x Connect the output and select the lock source. Connect the DA795 digital output to the
input of the DUT and select an internal crystal lock source, at the desired sample rate, on the Bottom Toolbar.
x Select the audio channel. Select either the left or right audio channel for testing.
x Select the test frequency. Set the Test Frequency field to the frequency at which you wish
to run the test. To set the generator frequency, click on the sine wave icon in the Bottom Toolbar to jump to the generator screen and select the desired sine wave test frequency.
x Set the level. Set the digital level of the sine wave test signal to 0 dB FS.
x Read the results. Read the distortion in dB or percentage.
Note that the notch filter frequencies are referenced to 48 kHz, so if other sample rates are detected at the input, the notch filter and generator frequencies will be scaled to that sample rate.
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DIGITAL TESTS
The Digital Tests menu contains functions that are used to test equipment, and to isolate potential problems. The input source for these tests is Digital Input 1 and/or Digital Input 2. The Digital Tests menu includes the following tests:
Digital Lock Test Video Lock Test Transparency Test Latency Test Jitter Meter
The Digital Tests menu, showing the available test functions.
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Digital Lock Test
Description
The Digital Lock Test tests whether a digital input (AES/EBU or S/PDIF) is locked to another digital input, to the word clock, a super clock, ADAT input or ADAT sync. It uses very accurate frequency counters to determine signal lock. Differences in frequency of less than 0.01 Hz are detected, which provides lock verification to better than 1ppm.
Digital Lock Test Applications
x Check for lock between two digital signals. x Check whether a digital signal is locked to a word clock or super clock.
Digital Lock Test Display/Controls
Top Toolbar. The Top Toolbar provides input select fields.
Note that if the frequency difference is large (defined here as greater than 4 Hz) the signals are considered out of lock. If the difference is less than 4 Hz, but greater than 0 Hz, the signals are considered “drifting.” If the frequency difference is 0 Hz, the two signals are considered locked.
Signal 1 Frequency
Frequency Drift
Scale
o Signal 1 Frequency. The frequency of the signal at the Digital Input 1 connector.
o Signal 2 Frequency. The frequency of the signal at the Digital Input 2 connector.
o Frequency Drift. The difference in frequency between the two signals.
o Frequency Drift Scale. Displays the frequency difference with a pointer on a logarithmic
distortion bar scale. The midpoint marks are at 0.2 and 0.5 of the value of the marked points to their right (0.2, 0.5; 1.2, 1.5; 2, 5; etc.).
Signal 2 Frequency
Frequency Drift
Digital Lock Test Operation
x Connect and select one input signal. Connect a digital signal to one of the Digital Input 2
connectors; AES/EBU, or S/PDIF. Select this input on the Top Toolbar.
x Connect and select a second input signal. Connect the signal to check for lock to either
Digital Input 1, a word clock (Fs) or super clock (256xFs) to the BNC input, an ADAT signal
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to the input optical connector, or an ADAT sync signal to the DB-9 connector. Select this input on the Top Toolbar.
x Read the results. Read the absolute frequency drift on the numeric display, or on the
horizontal bar scale.
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Video Lock Test
Description
The Video Lock Test allows you test whether a digital audio signal in AES/EBU, S/PDIF, or ADAT format is locked with a video sync signal (black burst). It uses very accurate crystal-based frequency counters to determine signal lock. Differences in frequency of less than 0.01 Hz are detected, which provides lock verification to better than 1ppm. Results are shown in terms of video frames per hour of drift. Note that since the BNC input connector is used for the video input, it is not possible to compare video sync directly with either word clock or super clock (signals that are normally on a BNC line).
Since the signals we are comparing are several orders of magnitude different in frequency, true synchronicity testing (like a phase comparison) is not practical. Rather, the ratio of frequencies is computed and compared to an ideal ratio to determine the amount of drift between the video signal and the digital audio signal.
The DigiPro compares the digital audio frequency to a list of known, typical sample rates, and the nearest sample rate is chosen. We call this the Nominal Sample Rate. The same is done for the video frame frequency, to determine the Nominal Video Rate. The ideal frequency ratio is determined and the actual frequency ratio of the two signals is
then compared to the ideal ratio, to determine the amount of drift, using this formula:
Vf/hr = ABS(1 – (VRa/VRn * SRn/SRa)) * 3600 secs/hr * VRn
Where:
VRa = Actual Video Rate VRn = Nominal Video Rate SRa = Actual Sample Rate SRn = Nominal Sample Rate
The drift result is in units of Video Frames per Hour.
It is assumed that the audio track was recorded at a “normal” sample rate. These include the standard 32 kHz, 44.1 kHz, 48 kHz, 88.2 kHz, and 96 kHz rates, as well as these rates pulled up or down by 0.1%. It is important to know the intended sample rate of the audio. The Video Lock Test will show lock, if the audio is playing at a correct ratio, even if the sample rate at which the audio is playing is not the rate at which it was recorded.
Note that if the phase difference is large (defined here as greater than 4 video frames per hour (vf/hr) the signal is considered out of lock. If the difference is less than 2 vf/hr, but greater than 0 vf/hr, the signal is considered “drifting.” These values are arbitrary, and in cases of true lock the drift will be less than
0.1 video frames per hour.
Video Lock Test Applications
x Check lock between a digital audio signal and a video signal to determine whether an audio
track is locked to a video signal.
x Test whether a piece of equipment is able to lock to video and generate digital audio that is
locked to that video.
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Video Lock Test Display/Controls
Digital Sample
Rate
Frame Drift
Scale
Video Frame Freq.
Frame Drift/hr.
o Digital Sample Rate. The actual sample rate of the signal at Digital Input 1. o Video Frame Frequency. The frame rate of the video signal at the BNC Video In connector.
o Frame Drift/hr. Drift, in units of video frames per hour.
o Frame Drift Scale. Displays the frame drift with a pointer on a logarithmic bar scale. The
midpoint marks are at 0.2 and 0.5 of the value of the marked points to their right (0.2, 0.5;
1.2, 1.5; 2, 5; etc.).
Video Lock Test Operation
x Connect and select a video input signal. Connect a video sync signal to the BNC input.
x Connect and select a digital audio input signal. Connect a digital audio signal to Digital
Input 1, an ADAT signal to the input optical connector, or an ADAT sync signal to the DB-9 connector. Select this input on the Top Toolbar.
x Check the frequencies. Verify that both the digital signal sample rate and the video frame
rate, shown on the DigiPro screen, match the intended signal frequencies.
x Read the result. Read the amount of drift in video frames/hour.
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Transparency Test
Description
The Transparency Test checks whether a piece of digital equipment passes a signal without modifying it. The Transparency Test supplies one of several bit pattern test signals to the DUT (Device Under Test) input, then monitors the DUT output for that pattern. Any errors are counted and logged.
Transparency Test Applications
x Test digital recording equipment to check whether whatever is recorded digitally will play
back unaltered. This test is even more important when encoded signals, such as Dolby E, are recorded using PCM recorders.
x Test DAT machines, digital multi-track recorders, or CD recorders. x Check whether a DAW will pass a transparency test at unity gain (it should). If ANY gain,
attenuation, EQ, compression, reverb, or other effects are present, the test will fail.
x Test an ISDN line, or any long-distance digital audio transmission line that is supposed to be
lossless. You can send the test signal out and back, or record the test signal and send it back from the other end.
The DigiPro Transparency Test can run synchronously (analyzing the input as the DigiPro generates the test signal), or asynchronously (analyzing a previously recorded signal, or a signal transmitted from a remote location).
Transparency Test Display/Controls
L / R Input
Test Waveform
DC Value
Errors L / R
o L / R Input: Shows the digital input values as hex values during the test. o Output: Shows output digital hex values during the test. o Test Waveform:
x Walking 1s. One bit is set to 1, the rest are set to 0; the single 1 bit moves one bit left each
update.
Output
x Walking 0s. One bit is set to 0, the rest are set to 1; the single 0 bit moves one bit left each
update.
x Monotonicity. The value of the word increases by 1 each update (0, 1, 2, 3, …to max
value for the selected word length).
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x Digital DC. You may select any particular word value, in hex, for the output signal.
o DC Value. Used to set the output value for the Digital DC test waveform. o Errors L / R. Displays the number of errors since the test was started, for both the left and
right channels. After an error field reaches its maximum value of 65,536, it wraps back around to 0.
Transparency Test Operation
x Connect the output and select the lock source. Connect any digital output from the
DA795 to the DUT (Device Under Test). Select the desired output lock source and word length from the Bottom Toolbar.
x Connect and select the input signal. Connect the output of the DUT to one of the Digital
Input 1 connectors; AES/EBU, S/PDIF/Toslink, or ADAT. Select this input on the Top Toolbar. Or, record the test signal and play it back from the device under test.
x Run the test. If running synchronously, turn on the test using the signal generator on/off
icon on the Bottom Toolbar. If running asynchronously, turn on the output and record the test signal for as long as you wish the test to run.
x Read the results. Once lock occurs, you will ideally see a 0 in both left and right Errors
columns. Any non-zero result indicates that the DUT is modifying the digital signal in some way. If you wish to clear the error fields, just click on the word “Errors:.” Note that when many errors are occurring, such as loss of lock, the error field will “wrap” back around to 0 after it reaches its maximum value of 65,536.
x Troubleshoot errors. If the Transparency Test is recording errors, you should first verify
that no EQ, compression, or other signal modifiers are present. Next, turn off any sample rate converters, even if the incoming and outgoing sample rates are nominally identical. If you still have errors, try using the Digital DC waveform. Set a simple value, such as 000100 hex, and see what you are getting back. In some cases, you will be able to tell something from the return value.
o Value exactly one less. If you send out 000100 and get back 0000FF (one less in hex)
you should suspect that a multiplier is in the circuit, and is not being removed when unity gain is selected.
o Value exactly double. This may indicate that the digital stream is being doubled, for
example by monitoring a signal and also feeding a copy of it back in.
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Latency Test
Description
The Latency Test measures the amount of delay (latency) that a piece of digital equipment is applying to a signal. Results are shown both in numbers of clock samples and
Latency Test Applications
x Test latency through digital systems, such as live or broadcast systems, to eliminate phase
errors.
x Test the delay through an analog to digital converter (ADC). This is useful if you are using
several converters while recording, to determine that the difference in delays between channels does not cause phasing errors in the recorded signal.
x Test the delay through a DAW or digital recording console. Differences in delay through
different paths in a console can contribute to phase errors.
Latency Test Display/Controls
in milliseconds. The Latency Test can be performed on a piece of equipment with a digital output and either a digital or analog input.
Run/Pause
Signal Delay Samples
Signal Delay ms
Output Type
o Run/Pause. Click on the Run icon to start the test. (The icon then changes to the Pause icon,
which is used for freezing results.)
o Signal Delay Samples. Displays the signal delay time, rounded to the closest number of
clock samples.
o Signal Delay ms. Displays the signal delay time in milliseconds.
o Output Type. Selects whether an analog or digital output signal is fed from the DigiPro to
the input of the device under test.
Latency Test Operation
x Connect the output and select the lock source. Connect any digital output from the
DA795 to the DUT (Device Under Test). Select the desired output lock source and word length from the Bottom Toolbar.
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x Select the output type. You can select analog or digital output. Select analog when you are
testing the delay of analog-to-digital converters. Select digital for testing delay through digital systems.
x Connect and select the input signal. Connect the output of the DUT to one of the Digital
Input 1 connectors; AES/EBU, S/PDIF/Toslink, or ADAT. Select this input on the Top Toolbar.
x Run the test. Click on the Run icon to start the test. If testing an analog to digital converter,
you may need to adjust the converter input level or DA795 analog output level to avoid clipping at the converter input stage.
x Read the results. Read the signal delay, both in number of clock samples, and in
milliseconds (ms).
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Jitter Meter
Description
The Jitter Meter measures the RMS interface jitter through a digital AES/EBU or S/PDIF input, or the RMS clock jitter through the BNC input. Interface Fs jitter is measured in the range of 150ps to 100ns. Clock jitter (sample clocks at Fs or super clocks at 256xFs) is measured in the range of 35ps to 100ns. Jitter is measured directly, rather than
Jitter Meter Applications
x Measure jitter on digital outputs from any digital equipment. x Directly measure high-speed digital clocks, with a direct probe connected from the Word
Clock Input to an internal converter clock test point, to find the conversion jitter of ADCs or DACs.
Jitter Meter Display/Controls
being extrapolated from sideband information derived from an FFT of an analog domain signal.
The Jitter Test can be performed on a piece of equipment with a digital output and either a digital or analog input.
High Pass Filter
Jitter Scale
Jitter Indicator
o High Pass Filter: Applies a high pass filter to the jitter measurement at either 0, 50, 700,
1250 Hz
o Jitter Scale. Displays the Jitter RMS with a pointer on a logarithmic distortion bar scale. The
midpoint marks are at 0.2 and 0.5 of the value of the marked points to their right (0.2, 0.5;
1.2, 1.5; 2, 5; etc.).
o Jitter Indicator. Indicates the jitter as a value. Indicates “low” when the jitter is extremely
low.
Jitter Meter Operation
x Connect and select the input signal. If you are measuring jitter on an AES/EBU or S/PDIF
line, connect to Digital Input 2. If you are measuring jitter on a clock line, connect to the BNC clock input. Select the appropriate input on the Top Toolbar.
x Select the clock lock source in the bottom ToolBar. Usually, you will want to select one
of the internal crystals such as “Int 48k.”
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x Read the results. The jitter is shown in the scale and/or displayed as a measurement value
below the scale in nonoseconds (nS) or picoseconds (pS).
Note: The internal analog-to-digital converter (ADC), which is used to measure the output of the jitter board, is clocked by the system master clock. For this reason, a valid master clock is required for this function to work. If you get the message “VALID MASTER CLOCK REQUIRED,” then the selected clock (which may be set to the external word clock, for example) is not valid. Select a different master clock on the bottom toolbar, such as one of the internal crystals.
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SYSTEM TOOLS
The System Tools menu contains general purpose digital audio tools. The standard input source is Digital Input 1. The System Tools menu includes the following functions:
Level Meter LAeq Dialog Level Signal Generator Sweeps Pass Mode
The System Tools menu, showing the available functions.
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Level Meter
Description
The Level Meter measures the level of both left and right channel PCM audio signals within an AES, S/PDIF, or ADAT digital audio signal, from 0 dB FS to –135 dB FS. 0 dB FS indicates the highest level audio signal that can be represented by the word length currently in use.
The Level Meter function includes two meters: a stereo audio level meter and a stereo VU/PPM bar graph meter. Click the Level/VU Meter Mode field at the top of the display to switch between the Signal Level and the VU/PPM display modes.
The Level Meter measures the Left and Right input levels simultaneously, using The Digital Input 1 connectors, and provides a digital, numeric display.
The VU/PPM meter provides a standard left and right channel VU display. The absolute signal level to which the meter’s 0 VU point is referenced may be adjusted from 0 to +24 dB FS.
The PPM (Peak Program Meter) indicator is shown as a single bar that bounces above the main bar on program audio, indicating the instantaneous program peaks. The PPM meter uses the same reference level as the VU meter.
Level Meter Applications
x Measure digital signal levels, in dB, and calibrate equipment levels. x Monitor digital audio program material with the VU/PPM meter.
Level Meter Display and Controls
Level Screen. The Level screen provides a stereo audio level meter. Click on the “Level” title to
switch to the VU/PPM screen.
Units
Level Level
o Units. The same measurement units are selected for both channels. Select one of the
following signal level units: dB rms – dB level of the waveform true RMS voltage, with 0 dB referenced to full digital
scale.
dB peak – dB level of the waveform peaks, with 0 dB referenced to full digital scale. % rms – Percentage of full digital scale of the waveform true RMS voltage.
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g
% peak – Percentage of full digital scale of the waveform peaks.
o Level. These fields display the left and right channel levels of the digital audio signals
present at the input connector.
VU/PPM Screen. The VU/PPM screen provides a stereo VU/PPM bar graph meter. Click on the “Level” title to switch to the VU/PPM screen. Click on the “VU” title to switch back to the Level screen.
Ref. Level
Left VU Meter
Right VU Meter
Left VU Meter
Max Peak Meter Left
PPM Meter
Right VU Meter
Max Peak Meter
ht
Ri
o VU Reference Level. This field sets the absolute signal level to which the meter’s 0 VU
point is referenced. It can be adjusted from 0 to 24 dB FS. This corresponds with 0 to -24 dB FS.
o VU Graphic. Graphic VU display of the Left and Right levels, relative to the reference level
set.
o VU Numeric. Numeric VU display of the Left and Right levels, relative to the reference
level set.
o PPM Meter. The PPM (Peak Program Meter) indicator is a single bar that bounces above the
main bar. It uses the same reference level as the VU meter.
o Max Level. The maximum peak level is shown for both the Left and Right inputs.
o Max Reset. Highlight and click the left channel Max title field to reset the peak readings.
Level Meter Operation
x Connect and select the input signal. Connect a digital signal to one of the Digital Input 1
connectors; AES/EBU, S/PDIF/Toslink, or ADAT. Select this input on the Top Toolbar.
x Select the Level Meter mode. Use this mode when measuring constant level test signals.
x View the results. The dB level or percent level will be displayed.
x Select the VU/PPM Meter mode. Use this mode when monitoring changing program
audio.
x View the results. The VU and peak program indicators show the changing program audio
levels.
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LAeq Dialog Level
Description
LAeq Dialog Level computes the average RMS level of the mixed (combined) digital audio signal from Digital Input 1. This information can be used to set the Dolby Digital dialog level constant (dialnorm) in a
5.1 stream. LAeq stands for the A-weighted long-term average audio level. The DTV spec for broadcast AC-3, for example, is that the program material be transmitted at -27 dB FS LAeq. This means that the A-weighted long-term average level
LAeq Dialog Level Applications
x Determine the equivalent dialog level for Dolby Digital (dialnorm), or for any digital audio
signal.
of the program material is 27 dB below maximum digital level (0 dB FS). The DigiPro assists broadcasters in meeting the FCC A/53 Annex B 5.5 Dialogue Level spec. It allows them to set their DTV encoder dialnorm parameter to the average value measured with the DigiPro, at the encoder input. The LAeq Dialog Level allows you to easily set different mixes to the same perceived loudness level.
LAeq Dialog Level Display/Controls
Run/Pause
LAeq Level
Test Time
o Run/Pause. Click on the Run icon to start the test. (The icon then changes to the Pause icon,
which is used for freezing results.)
o LAeq Level. Displays the A-weighted long-term average audio level of the program
material, referenced to maximum digital level.
o Test Time. Indicates the elapsed test time.
LAeq Dialog Level Operation
x Connect and select the input signal. Connect a digital signal to one of the Digital Input 1
connectors; AES/EBU, S/PDIF/Toslink, or ADAT. Select this input on the Top Toolbar.
x Run the test. Click the Run/Pause icon to start the function. Allow the function to run for
the desired amount of time. The elapsed test time is shown on the screen. Longer test times give a better representative sample of the long-term average audio level.
x Read the results. The LAeq level of the digital audio signal is shown, in dB FS.
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Signal Generator
Description
The DigiPro Signal Generator is a full­featured, crystal-controlled signal generator that creates digital test signal test tones and standard noise waveforms. The Digital Generator creates test waveforms that are sent to the Digital Audio Outputs, and are converted to analog that is sent to the Analog Audio Outputs. Many of the Signal Generator controls can be accessed on the Bottom Toolbar of any DigiPro function, without having to exit the function. These Bottom Toolbar generator controls include On/Off, level (in 1 dB steps), word length, and generator lock source. The Generator screen gives you additional generator control, however, compared to the
Generator controls in the Bottom Toolbar of the other functions. In the Generator screen, you can select the waveform type and frequency, set the output level with greater resolution, and view level indicators of the digital and analog signal outputs. The Signal Generator can be entered either directly, from the Tools menu, or by clicking on the sine icon on the Bottom Toolbar of any function. If entered from the toolbar, exiting the Generator screen returns you to the original function. Note: You can store default values for generator waveform type, frequency, and level, by using the Save Defaults function in the Utilities menu.
Signal Generator Applications
x Create accurate digital audio reference signals.
Signal Generator Display/Controls
Waveform Type
Audio Frequency
Digital Level Graph
Level Control
Analog Voltage
Outputs
o Waveform Type. Displays the selected audio waveform type. Click on this field to select
between Sine wave, Square wave, White noise, or Pink noise.
Frequency Step
o Audio Frequency. Displays the selected single frequency for sine wave or square wave
output waveforms.
o Frequency Step. Provides octave, 1/3 octave, or fine adjustment of the sine or square wave
output frequency. Click on the field to select the desired frequency step for the sine wave or square wave frequency adjustment.
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o Digital Level Graph. Indicated digital audio output level. The digital audio level can be
adjusted from 0 db FS to –140 dB FS.
o Level Control. The level can be adjusted from the Generator screen Level Control field, in
10, 1, or 0.1 dB steps, or from the Bottom Toolbar, in 1 dB steps.
o Analog Voltage Outputs. Indicates the actual analog audio output voltages on the
unbalanced (RCA phono) and balanced (¼” TRS) Analog Audio Output connectors.
Signal Generator Operation
x Enter the Signal Generator function screen. Click the Sine icon on the Bottom Toolbar of
any DigiPro function, without exiting the function. Or, select the Signal Generator in the System Tools menu.
x Select the desired waveform type.
x Select the desired audio frequency.
x Turn on the Generator. Use the On/Off control on the right side of the Bottom Toolbar.
x Adjust the output level. Adjust the Level Control for the desired digital audio level or
analog output voltage.
x Connect the Generator output. Connect the Digital Audio Output or Analog Audio
Output, as desired.
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Sweeps
Description
The DA795 provides two sweep modes: Amplitude sweep and Sine sweep. The sine sweep parameters are also applied to the amplitude sweep mode. You can set the beginning and ending frequencies between 20 Hz and 20 kHz, and sweep time from 1 to 99 seconds.
The amplitude sweep plots amplitude vs. frequency. The average signal level in each 1/3 or 1/12 octave band is measured as the frequency is stepped across the selected frequency range. The response is displayed
Sweeps Applications
x Use the Amplitude sweep to plot the frequency response of audio components.
graphically, and the measurement cursor can be used to read the level at the specific frequencies.
The sine sweep provides a stepped sine wave frequency sweep between two chosen frequencies over a chosen time period. Use this function to define the sweep parameters for the amplitude sweep function. You can set the beginning and ending frequency, and sweep time. The level is set by clicking the Gen field to jump to the Signal Generator control screen.
x Use the Sine sweep to step the audio frequency through a particular frequency range, for
system or component testing.
Sweeps Display/Controls
Amplitude Sweep Mode.
Mode Title
Run/Pause
Cursor Frequency
Frequency Limit
Cursor Level
o Mode Title. This title labels either the Amplitude Sweep mode or the Sine Sweep mode.
Click on the field to switch to the other mode.
o Run/Pause. Click on the Run icon to start the test. (The icon then changes to the Pause icon,
which is used for freezing results.)
o Measurement Cursor. The measurement cursor is a vertical bar that you can position
horizontally along the plot. It allows you to read the measured amplitude for each frequency
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point on the plot. To position the measurement cursor, click on the Cursor Frequency field to select it (underlined). Rotate the control knob to move the cursor to the desired frequency.
The value displayed in the Cursor Level field is the digital audio level (relative to the maximum digital level), at the frequency selected by the measurement cursor.
Sine Sweep Mode.
Run/Pause
Start Freq.
End Freq.
Sweep Time
o Mode Title. This title labels either the Amplitude Sweep mode or the Sine Sweep mode.
Click on the field to switch to the other mode.
o Run/Pause. Click on the Run icon to start the test. (The icon then changes to the Pause icon,
which is used for freezing results.)
o Start Frequency. Sets the starting sweep frequency for both the Sine and Amplitude sweep
modes. The frequency increments in 1/3-octave steps.
o End Frequency. Sets the ending sweep frequency for both the Sine and Amplitude sweep
modes. The frequency can be selected in 1/3-octave steps. The end frequency must be set higher than the start frequency for the sweep to run.
o Time Duration. Sets the time duration for both the Sine and Amplitude sweep modes. Times
from 10 to 99 seconds can be selected. When the sweep duration completes, the sweep cycle starts again and repeats indefinitely in the sine wave sweep mode. The amplitude mode sweeps through only one sweep cycle.
Sweeps Operation
Amplitude Sweep
1. Select the Sine Sweep mode and set the following parameters:
xStart frequency xEnd frequency xSweep duration, in seconds
2. Connect any of the DA795 digital or analog outputs to the input of the device under test. If you need to change the output signal level, click the Gen field and use the signal
generator control screen to set the desired level.
3. Select the Amplitude Sweep mode.
4. Connect the DUT output signal to Digital Input 1.
5. Click on the Run icon and wait for the sweep to finish.
6. Read the frequency response plot on the DA795 display. Use the measurement cursor to read dB values at individual frequencies.
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Sine Sweep
1. Select the Sine sweep mode.
2. Connect any of the DA795 digital or analog outputs to the device input.
3. Select the start frequency.
4. Select the end frequency.
5. Select the sweep duration, in seconds.
6. Click on the Run icon to run.
7. To change the DA795 output signal level, click the Gen field and use the signal generator control screen to set the output level.
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Status
Pass Mode
Description
The Pass Mode function is made to modify a digital signal. You are able to change channel status information, change the signal sample rate (sample rate conversion), change signal format, and add digital gain or attenuation.
Pass Mode Applications
x Simplify transfers between incompatible digital audio devices. Convert AES/EBU, S/PDIF
Coax and Toslink, or ADAT optical format digital audio streams to any other format. Convert from any sample rate to any other sample rate.
x Make your CD S/PDIF coaxial output at 44.1 kHz match a digital mixer AES input at 48
kHz or 96 kHz.
x Translate a pair of ADAT channels to AES or S/PDIF format, or send the AES or S/PDIF
input to the ADAT output.
x Provide jitter correction for any format or sample rate input, feeding to any format or sample
rate output, by locking to a stable internal crystal clock.
x Modify channel status information so that a piece of equipment can lock to a digital signal. x Lock a free-running digital signal to an AES stream, word clock, or ADAT signal. x Evaluate an A/D converter, using a low-level analog input signal and high digital gain. x Remove the copy bit (SCMS) from a consumer digital signal. x Up-sample a 44.1 kHz or 48 kHz signal to 88.2 kHz or 96 kHz. This can have an advantage,
when converting to analog, by pushing the conversion filters up above the audio spectrum.
The digital input data can be transferred to the digital output at the same sample rate at which it comes in, or it can be sample-rate converted by locking the output to another signal or clock.
Pass Mode Display/Controls
Input Channel
Reset
Digital Gain
o Input Channel Status.
Field 1: Status Use. (Pro/Con). AES3 connections generally send professional
data. SPDIF and Toslink connections generally send consumer data. This bit determines how other channel status information is interpreted.
Freq. Lock
Input Channel Status
Output Channel Status
SRC on/off
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Professional:
Field 2: Sample Rate. 32 kHz; 44.1 kHz; 48 kHz; not indicated (---) Field 3: Word Length. 16 to 24 bits; not indicated (---) Field 4: Channel Mode. 2ch; 1ch; not indicated (---) Field 5: Emphasis. CCITT J.17; 50/15 us; no pre-emphasis; not indicated (---)Field 6: Validity. PCM Audio; No PCM (V) Field 7: Fs Down Scaling. No scaling; Scale indicated sample rate by 1/1.001
Consumer:
Field 2: Sample Rate. 32 kHz; 44.1 kHz; 48 kHz; not indicated (---) Field 3: Word Length. 16 to 24 bits; not indicated (---) Field 4: Category Code. Code indicates equipment type. Field 5: Emphasis. 50/15 us; no pre-emphasis; not indicated (---)Field 6: Validity. PCM Audio; No PCM (V) Field 7: Copy Bit (SCMS). Copyright asserted; No copyright asserted
x Reset. Reset the Output Channel Status to be the same as the Input Channel Status.
x Output Channel Status. If desired, change any of the status items, including sample rate,
word length, copy protection, emphasis, or other items.
x Digital gain. You can apply digital gain to the signal. Up to 60 dB of gain may be added.
x SRC On/Off. This field indicates whether the input signal is being sample rate converted.
By choosing a second input signal, or an internal clock signal, as the Output Lock Source, the input signal is reclocked (sample rate converted) to the clock selected at the Output Lock Source. This is true whether the signal or clock selected as the output lock source is the same or a different sample rate, compared to the input signal.
x Output Lock Source. To send the signal out without changing the sample rate, select the
Output Lock Source to match the signal source. For example, if you are using the AES input, set the output lock source to AES/SPDIF. This will lock the output signal to the input signal. To use the sample rate converter (SRC), select one of the internal crystals, or the word clock or super clock.
Note: A valid output lock source is always required. Selecting the AES or S/PDIF input, and selecting ADAT as the output lock source will not work, for example, if there is no valid ADAT input signal. Selecting Super clock as an output lock source, when no signal is connected to the BNC input, will also not work. However, it will work to select ADAT as the input, and the AES input as the output lock source, if a valid AES input signal is present.
Pass Mode Operation
x Connect and select the input signal. Connect a digital signal to one of the Digital Input 1
connectors; AES/EBU, S/PDIF/Toslink, or ADAT. Select this input on the Top Toolbar.
x Connect the output and select the lock source. Connect the DA795 Digital Audio Output
back into your system.
x Modify the Output Status. If desired, change any of the status items.
x Apply gain. Apply any desired digital gain or attenuation to the signal.
x Use the output. The incoming digital signal will be modified and sent to the digital output.
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UTILITIES
The Utilities menu contains two general purpose digital audio functions. The Utilities menu includes the following functions:
Digital Cable Tester Capture Sample Data Save Defaults About
The Utilities menu, showing the available functions.
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eadout
Digital Cable Tester
Description
The Digital Cable Tester tests digital AES/EBU or S/PDIF cables for functional quality. The DigiPro digital cable tester uses the Julian Dunn J-test waveform to excite jitter in a digital audio cable, then uses the
The Digital Cable tester works only with AES and S/PDIF copper cables, not with optical cables. Optical cables do not induce jitter, since they do not have capacitance. To test an optical cable, use the Transparency Test, running at the maximum sample rate (96 kHz).
Digital Cable Tester Applications
x Measure the digital signal quality of various cables for troubleshooting or cable selection.
Digital Cable Tester Display/Controls
jitter detector circuit to measure the resultant jitter. Higher quality digital cables have lower capacitance, thus they induce less jitter in a signal transmitted through the cable.
Jitter Scale
Jitter dBr
Jitter R
Digital Cable Tester Operation
x Connect and select the input. Connect one end of the cable to be tested to one of the
Digital Input 2 connectors; AES/EBU or S/PDIF. Select this input on the Top Toolbar.
x Connect the output and select the lock source. Connect the other end of the digital cable
to the DA795 Digital Output. Select one of the internal crystals as the lock source.
x Read the results. Read the cable quality on the meter. Higher quality digital cables induce
less jitter into the test signal.
Note: The analog-to-digital converter (ADC), which is used to measure the output of the jitter board, is clocked by the system master clock. For this reason, a valid master clock is required for this function to work. If you get the message “VALID MASTER CLOCK REQUIRED” then the selected clock (which may be set to the external word clock, for example) is not valid. Select a different clock lock source on the bottom toolbar. You can always select one of the internal crystals.
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Capture Sample Data
Description
The Capture Sample Data function can be used to capture a buffer of data from the S/PDIF or AES input. It will capture data whether or not it is PCM (audio) data.
You can then scroll through the buffer to examine the data that is stored, and search for particular values. All data is shown and entered as 16-bit hex values. The size of the
Capture Sample Data Applications
x Compare the data actually being transmitted in an AES data stream, whether AES PCM
audio, AC-3 data, or MPEG data to the data that was intended to be transmitted.
Capture Sample Data Display/Controls
capture buffer is 0x0C00 (3,328 decimal) words.
This function was written to debug an AC-3 encoding algorithm, to compare the data being transmitted to the data stored on a DVD, in the audio tracks. No other device was found that could accomplish this with non-PCM audio data.
Start Stop Count Goto Search
Run/Pause
Checksum
Address Fields
Capture Status
Data Fields
x Capture Buffer. To begin capturing data immediately, make sure that all five Capture
Control fields (Start, Stop, Count, Goto, Search) are “0000,” and click the Play icon. Data will be captured, from the moment that you click the Play icon, until the buffer is full.
x Start Byte Value. Enter a 16-bit hex word value into the Start data field, and click the Play
icon. The Capture Status field indicates “Running....” until the specified value is detected in
one of the 16-bit values of the incoming PCM data stream. When the trigger value is detected, the capture begins, and continues until the capture buffer is full, unless a Stop value is specified, and is found before the buffer is full.
x Stop Byte Value. Enter a 16-bit hex word value in the Stop field, and a 16-bit hex value in
the Start field. When you click the Play icon, the DigiPro will not capture any data until the Start value is found in the incoming data. It will then continue capturing data until the Stop value is found, if set, or until the end of the capture buffer is reached.
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x Capture Bytes (Count). Enter a value into the Count field, leaving all of the other Capture
Control fields blank. When you click the Play icon, the DigiPro will capture the number of bytes entered.
x Address Fields. Capture buffer memory addresses are listed down the left side of the
screen, under the ADDR title, in steps of four (0000, 0004, 0008, etc.).
x Data Fields. The data in each listed buffer address is shown in the field just to the right of
that address, under the DATA title, and data in the following three addresses is shown in each successive field to the right.
x Checksum. To the right of the word “ADDR” is a 16-bit hex field. This value is the 16-bit
checksum of the bytes in the capture buffer. Even though the data can be thought of as 24­bit words, each byte is added individually to generate this checksum.
x Capture Status. Because a full buffer of data is normally captured almost immediately after
you click the Play icon, the Capture Status field normally indicates “Done” almost immediately. If a Start value has been set that doesn’t occur quickly in the incoming data, however, the Capture Status field indicates “Running...” until the specified value is detected.
After the data capture is done, you can inspect the data, go to a particular buffer address, or search for a particular data value.
x Address Scroll. Place the cursor on the first address field, under the text “ADDR.” Now click
and turn the Control Knob, and the display will scroll through memory addresses. This allows you to scroll through the buffer and inspect the data.
x Goto. To go to a particular address, enter it into the Goto address field. The display will be
adjusted to show this address. Note that this is a dynamic field, so as you change any digit, the display immediately moves to that location.
x Search. To search for a particular data value, enter it into the Search data field. Now click the
Play icon, and the buffer address listing will advance to show the location of the first occurrence of this value, if it is found in the capture buffer.
Capture Sample Data Operation
x Connect and select the input signal. Connect any AES data stream to one of the Digital Input
1 connectors; AES/EBU, S/PDIF/Toslink, or ADAT. Select this input on the Top Toolbar. This data stream can be normal digital audio (PCM), any encoded bitstream, such as AC-3 or DTS, or any other data stream that complies with the AES specification.
x Run the test. Click on the Run icon to start the capture.
x Inspect the Data.
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Save Defaults
Description
The following control fields can have their current setting saved as their default value:
o Digital input source. o Sub-menu choices on all functions. o Generator settings, including lock source, word length, frequency, and level.
Save Defaults Operation
To store the current settings so that the DA795 starts up next time set this way, set up the DA795 the way that you want it, go to the Save Defaults function on the Utilities menu, and select “Save” under Store settings. The next time you power up the DA795, your selections will be restored as the default settings.
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About
Displays the firmware version loaded into the DA795, along with technical support contact information.
54
GLOSSARY
This section defines common terms used in this manual.
ADAT – Alesis Digital Audio Tape. A digital audio transmission format invented and patented
by Alesis, originally for use with their digital tape recorders. Format usually runs at 48 kHz sample rate, with each frame containing up to eight channels of 24-bit digital audio. The physical connection uses fiber optics, using the same optical cable as Toslink.
ADC (Analog to Digital Converter) – An ADC converts an analog signal into the digital
domain. It runs at the desired sample rate – or, if over-sampling is used, at a multiple of the desired sample rate. At each sample time, the level of the analog signal is measured and converted into a number. (See Word Length).
AES/EBU –AES3 and IEC-985 define a balanced line signal that normally uses XLR connectors
to interconnect equipment. This format takes its name from the two principal advocates and is the professional audio data interface. This standard interleaves useful non-audio channel status data with the audio data, to provide information on the sampling rate, etc.
Bit Depth – See Word Length.
Clock rate – See Sample Rate.
DAC (Digital to Analog Converter) – A DAC converts a digital signal back to analog. The
samples are non-continuous (by definition), since there are a finite number of levels (see Word Length) and a finite number of samples in a second (see Sample Rate), so after conversion the numbers need to be smoothed (filtered) to get back to analog.
DAW – Digital Audio Workstation. A system designed to record, edit, and play back digital
audio. A key feature of DAWs is the ability to freely manipulate recorded sounds, much like a word processor manipulates typed words. Refers to a general combination of audio multitrack software and high-quality audio hardware —the latter being a specialized audio converter unit which performs some variety of both analog to digital (ADC) and digital to analog (DAC) conversion. Performs the same functions as a common sound card, but is an external unit, which records far less noise (hum, static), higher resolution, and better dynamic range.
dB FS - Decibel level of a digital audio signal, referenced to full scale digital output. In digital
systems, 0 dB FS equals the highest level (number) that the employed word length is capable of representing.
DigiPro – See DA795.
Dither – As a signal that is being converted from analog to digital gets to lower and lower levels,
and finally approaches the least significant bit, more and more information starts to be lost. The quietest sine wave you can play back is one bit in amplitude—and therefore plays back as a square wave. The lower the signal levels, the higher the relative distortion. Oddly, by adding low-level noise to the incoming signal (dither), the information starts coming through better, at the cost of more noise. By adding dither, we trade a little low-level hiss for a big reduction in distortion. The theory behind this is a little messy, but imagine looking through your spread fingers. You see some things, but some things are blocked by your fingers. Now wiggle your hand side to side, and you can see through everything through your fingers, at the cost of some blurring.
DA795 – DigiPro Digital Audio Analyzer.
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DUT – Device Under Test, the unit being tested. Fs – Sample Frequency. See Sample Rate.
Hex – Short for hexadecimal, or base 16 number system. A digit is 0-9 or A-F (A=10, B=11,
...F=15). Although computers work in binary arithmetic (1s and 0s only), it is considerably easier for programmers and others to work with computer and digital audio numbers in hex. Here are some examples:
Decimal Hex 0
0000
1 0001 15
000F
16
0010
-1 FFFF
Lock – In this context, lock refers to a property of two or more digital audio devices or data
streams. If lock is present, then the devices or data streams are aligned, at least on the word level. Signals that are not locked are referred to as “out of lock.”
Nyquist Frequency – One half of the sample rate. No audio data can be stored or represented
above this frequency. Just think of plotting samples. As the audio frequency goes higher and higher, there are fewer samples per wavelength. When you finally hit exactly two samples per sine wave (think of the top and bottom points of the sine wave), that is equal to the Nyquist frequency. Any higher audio frequency, and you won’t have even two points on the sine wave. If you keep going, the data actually shows up at a lower frequency – at one half the frequency of what it is supposed to be. So, very steep filters (so-called brick wall filters) are used to remove frequencies above the Nyquist frequency.
S/PDIF – (Sony/Philips Digital Interface) - defined by IEC-958 and AES-3. This unbalanced
signal is commonly connected via coaxial BNC or RCA phono connectors. This format is actually just another mode defined by AES/EBU, a direct descendant of the IEC-985. It is the ‘consumer’ mode that forgoes some of the less relevant status information, but does add the SCMS copy protection system.
Sample Rate – The number of times per second an analog signal is sampled to develop a
representative digital byte (word). The rate at which digital audio samples (words) are captured or transmitted. In general, faster is better. No audio at any frequency higher than one half of the sample rate can be represented. So, a digital signal with a 44.l kHz sample rate cannot contain any audio above 22,050 Hz. In most cases, the roll-off occurs lower, to prevent any data from sneaking in and aliasing (showing up at one half of its frequency). Also see Nyquist Frequency.
Status Bytes – The AES3 standard provides for status bits in a digital stream. The idea is that
information about the format of the data is embedded within the data stream. Information such as the sample rate, word length, emphasis, copyright, consumer, pro, and more is stored here. A few bits are stored in each frame. It takes 192 frames (left-right sample pairs) to store all of the data. A digital audio receiver extracts this data as the frames occur.
Super clock – A square wave that runs at 256 times the sample rate (256xFs). It is used as an
alternative to word clock to lock digital audio devices together.
Toslink – Defined by Toshiba as a specification that combined the S/PDIF digital signal protocol
with a cheap optical interconnect (those square plugs), designed specifically for consumer
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and prosumer equipment. The term 'Toslink' is now often used generally to describe that particular type of optical cable and connector, regardless of the digital data stream.
Word Clock –A square wave signal that runs at the sample frequency (Fs). Word clock is often
used to lock (synchronize) digital audio devices. The idea is that there is one master word clock which is fed to all digital audio devices, so that all digital audio that may be fed between the devices is locked together.
Word Length – Same as bit resolution. Number of bits per digital sample. CDs are 16-bits,
which allows for ±32767 different loudness levels. 20 bit allows ±524287 different levels, and 8-bit only ±127. So at a given sample rate, more bits are better. However, even if an analog to digital converter is “24 bit,” it doesn’t mean that you get all that resolution. In reality, the converter noise may be 17-21 bits, so you wouldn’t get the full advantage. And, there are high-resolution 1-bit systems. By running very high sample rates, the overall resolution increases.
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WARRANTY AND SERVICE INFORMATION
WARRANTY
Your DA795 Digital Audio Analyzer has been built to the highest quality standards in the industry. Each unit has been tested, aged under power for at least 24 hours and every function and range was retested to insure it met all published specifications. Your instrument is fully protected with a 1-year warranty.
SERVICE
Save the original shipping carton and packing material for reuse should you ever need to ship your generator, or return it to the Sencore factory for repair.
1. If you are returning the unit to Sencore for service, call the service department at the number below
and enclose the following information: owner's address, billing information, purchase order (if applicable), name and phone number of contact person, description of problem and reason for return. No return authorization is required.
2. Completely enclose the unit inside a plastic bag to protect its finish and prevent foreign material from
getting inside.
3. Cushion the unit equally on all sides with a minimum of 3 inches of padding material. Pack the
padding tightly enough to prevent the unit from shifting during shipment.
4. Seal all seams on the container with strapping tape.
5. Send the packed unit to the following address (we recommend shipping via United Parcel Service):
SENCORE FACTORY SERVICE 3200 Sencore Drive Sioux Falls, SD 57107
Most service repairs are completed within 72 hours. If you need to ask about your unit, the Sencore Service Department phone number is:
1-800-SENCORE (736-2673) or FAX (605) 339-7032
Fill in for your records:
Purchase date: _________________________
Hardware Serial Number (on bottom of unit) _______________________
Firmware Serial Number (on Utilities / About screen) _______________________
Software Version (on opening power-on screen) _________________________
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3200 Sencore Drive Sioux Falls, SD 57107 Call 1-800-SENCORE (736-2673)
www.sencore.com with your time in mind.
Form7494 Printed in U.S.A.
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