NTI NEU-AL1 User Manual

ACOUSTILYZER

User Manual

AL1

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© NTI AG
All rights reserved.
Subject to change without notice.
Release 1.30e / May 2006 / Software A1.30 or higher

MiniLINK, Minilyzer, Digilyzer, Acoustilyzer, Minirator, MiniSPL and
Minstruments are trademarks of NTI.

NTI contact details:

NTI AG
Im alten Riet 102
9494 Schaan
Liechtenstein, Europe
Tel. +423 - 239 6060
Fax +423 - 239 6089
E-mail [e-mail]
Web www.nt-instruments.com

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Index:

1. Introduction 4

CE Declaration of Conformity 5
International Warranty and Repair 6
Warnings 7
Test & Calibration Certicate 7

2. Overview 8

Acoustilyzer Functions 9
Easy Operation 9
Connectors 10

3. Basic Operation 12

Start-up Screen 13
Menu Bar 13

4. Measurement Functions 22

SPL/RTA - Sound Level Meter 23
SPL/RTA - Real Time Analyzer RTA 27
Reverberation Time RT60 36
FFT Analysis 42
Polarity Test 46
Delay Time 48
Electrical Measurements - RMS/THD 51
Speech Intelligibility STI-PA (optional) 53
Calibration 61

5. MiniLINK PC Software 64

Installation 64
Start the MiniLINK PC Software 65
Free Registration of your Test Instrument 66
Read Out of Stored Test Results 67
Visualizing the Test Results 68
Test Result Logging at the PC 72
Remote Test Instrument Control with the PC 74
MiniLINK Tools 75
Activate Options 81

6. Troubleshooting 82

7. Accessories 83

8. Technical Specication 85

9. Appendix: Introduction to STI-PA 88

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1. Introduction

Congratulations and thank you for buying NTI’s Acoustilyzer AL1, a
product specially suited for professional acoustical test applications. The
Acoustilyzer offers advanced acoustics functions including an optional
speech intelligibility STI-PA measurement module and further basic
electrical features. We are convinced you will enjoy using it!

This manual describes the Acoustilyzer AL1 functions and measurements
in detail. Further application information about the acoustical and electrical
measurements can be found on the web site “www.nt-instruments.com”.

The Acoustilyzer AL1 is available as stand alone test instrument or as
crossgrade package for existing Minilyzer ML1 users. The same crossgrade
option can be used to install the Minilyzer functionalities on the AL1. The
STI-PA measurement feature is optional.

The product packages includes the following items:

Acoustilyzer AL1 1x Acoustilyzer AL1

1x MiniLINK CD (PC software)

1x MiniLINK USB Cable

1x Acoustilyzer Test CD

1x Acoustilyzer User Manual

ML1-AL1 Crossgrade 1x MiniLINK CD (PC software)

1x Acoustilyzer Test CD (audio samples)

1x License Number Crossgrade

1x Acoustilyzer User Manual

1x Minilyzer User Manual

STI-PA Measurement
Option

1x STI-PA Test CD (STI-PA test signal)

1x License Number STI-PA

1x Acoustilyzer User Manual

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CE Declaration of Conformity

We, the manufacturer

NTI AG
Im alten Riet 102
9494 Schaan
Liechtenstein, Europe

hereby declare that the product Acoustilyzer AL1, released in 2004,
conforms to the following standards or other normative documents.

EMC-Directives: 89/336, 92/31, 93/68
Harmonized Standards: EN 61326-1

This declaration becomes void in case of any changes on the product
without written authorization by NTI.

Date: 1. September 2004

Signature:

Position of signatory: Technical Director

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International Warranty and Repair

International Warranty

NTI guarantees the functionality of Acoustilyzer AL1 against defects in
material or workmanship for a period of one year from the date of original
purchase, and agrees to repair or to replace at its discretion any defective
unit at no cost for either parts or labor during this period.

Restrictions

This warranty does not cover damages caused through accidents, misuse,
lack of care, the attachment or installation of any components that were
not provided with the product, loss of parts, connecting the instrument to
a power supply, input signal voltage or connector type other than specied
or wrongly polarized batteries. In particular, no responsibility is granted for
special, incidental or consequential damages.
This warranty becomes void if servicing or repairs of the product are
performed by any party other than an authorized NTI service center or if
the instrument has been opened in a manner other than specied in this
manual.
No other warranty, written or verbal, is authorized by NTI. Except as
otherwise stated in this warranty, NTI makes no representation or warranty
of any kind, expressed or implied in law or in fact, including, without
limitation, merchandising or tting for any particular purpose and assumes
no liability, either in tort, strict liability, contract or warranty for products.

Repair

In case of malfunction, take - or ship prepaid - your NTI Acoustilyzer
AL1 packed in the original box, to the authorized NTI representative
in your country. For contact details see the NTI web page
“www.nt-instruments.com”.

Make sure to include a copy of your sales invoice as proof of purchase
date. Transit damages are not covered by this warranty.

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Warnings

In order to avoid any problems during the operation of the instrument, follow
the rules listed below:

• Use the instrument for the intended purpose only.

• Never connect the instrument to a high voltage output such as
a power amplier, mains power plug, etc.

• Do not disassemble the instrument.

• Never use the instrument in a damp environment.

• Remove the batteries as soon as they are at or if the instrument
is not intended to be used for a longer period of time.

Test & Calibration Certicate

This is to certify the Acoustilyzer AL1 is fully tested to the manufacturer’s
specications. NTI recommends to calibrate this test instrument
one (1) year after purchase. Thereafter the calibration- and adjustment
interval is subsequently one (1) year.

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2. Overview

The Acoustilyzer AL1 is a sophisticated
tool used to analyze acoustical signals.
It is designed for easy and quick detailed
analysis of the acoustic environment
and to carry out the most important
electrical measurements. An accurate
overview of the actual acoustical signal
is displayed on a large LCD.

The AL1 is a class 1 accuracy instrument
and available with the measurement
microphones MiniSPL (class 2) or
M2010 (class 1 frequency response).
Alternatively other measurement
microphones can be used.

Class 1 acoustics analyzer

NTI offers the class 1 frequency response
microphone M2010 (an external
phantom power supply is required).
The Acoustilyzer in combination with
the M2010 measurement microphone
forms a highly accurate class 1
acoustics analyzer.

Class 2 acoustics analyzer

The Acoustilyzer in combination with
the MiniSPL forms a comprehensive
class 2 acoustics analyzer. MiniSPL
is a battery powered measurement
microphone. It is the ideal accessory for
the Acoustilyzer.

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Acoustilyzer Functions

The Acoustilyzer AL1 features many
measurement functions, which are
accessible through a drop down menu bar.

The base element is the cursor (inverted
area), which may be navigated through the
various functions by using the cursor keys.

• SPL/RTA: Sound pressure level & time-averaged sound pressure

level (LEQ) measurements of wideband, octave or 1/3
octave values

• RT60: Reverberation time with 1/1 octave band resolution

• FFT: Real time zoom FFT

• POLARITY: Polarity measurement of speakers and line signals

• DELAY: Delay time measurements between speakers

• RMS/THD: Level and distortion measurements

• STI-PA: Speech intelligibility measurement (only visible after

received STI-PA license activation key)

• CALIBRTE: Calibration of connected measurement microphone

Easy Operation

Unit selected with cursor to
change setting

All selectable settings may be adjusted
simply by

• Pressing the enter key to select the

requested value.

• Alternatively at longer selection lists the

chosen eld is ashing. Now select the
requested value with the cursor keys.
Conrm the setting by pressing the
enter key again.

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Connectors

On top of the AL1, three connectors as well as the internal microphone are
located:

• The XLR and RCA inputs allow to feed a signal to the AL1.

• A 3.5 mm (1/8“) jack monitor output allows the connection of a
headphone. Thus, the user may hear any electrical input signal.

• The internal microphone is used to test the polarity of loudspeakers
and for delay time measurements. SPL measurements are not
supported with this internal microphone.

XLR & RCA
Inputs

Monitor
Output

Internal
Microphone

Note: Never connect the XLR- and the RCA input at the same time!

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Battery Replacement

After unpacking, insert three (3) pcs. 1.5 V alkaline batteries, type AA, LR6,
AM3 into the AL1 battery compartment as shown below. The typical life­time for a set of alkaline batteries is 16 hours.

Notes:

• We do not recommend to use rechargeable NiCd- or NiMH­batteries.

• Do not insert batteries of different types.

• Replace all batteries at the same time - never mix old and new
batteries.

• Note the correct polarities of the inserted batteries.

• Remove the batteries as soon as they are at and change all
batteries at the same time.

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3. Basic Operation

In spite of the wide range of available measurement functions and optional
setups, the operation of the Acoustilyzer is almost self-explanatory.

Menu Bar

Test Result

Power On/Off­Backlight

Escape
button

Enter / Cursor
Keys

The LCD is divided in the menu bar on top and the measurement results
displayed below.

The cursor keys and the escape button allow straightforward navigation
through the available features

• Actual settings (measurement function, filters)

• Measurement results (numerical or graphical display)

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Start-up Screen

The start up screen remains displayed by
pressing and holding any button during the
start up of the unit. This supports e.g. the
read out of the instrument serial number
from your device. The serial number
starts with three letters (such as e.g.
ANK675A2A2).

After the successful registration of the AL1
the start-up screen may be customized.
See details in “Customizing start-up screen”
later in this user manual.

Menu Bar

The menu bar allows the selection of the basic test congurations.

Measurement
Functions

Screen
Selector

Memory Menu
& Battery Status
Indication

Input
Filters

Setup
Screen

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Measurement Functions

• SPL/RTA: SPL & RTA measurement

• RT60: Reverberation Time

• FFT: Real time zoom FFT

• Polarity: Speaker polarity

• Delay: Delay time

• RMS/THD: RMS level and distortion

• STI-PA: Speech intelligibility

• Calibrte: Calibration menu

Screen Selector

The Acoustilyzer features the SPL/RTA,
RT60 and STI-PA function with two different
test result screens.

e.g. the SPL/RTA “123” is showing the
sound level meter screen and the marked
graphical symbol shows the real time
spectrum analyzer.

Short-cut

Hold the ESC button down and additionally
press the left or right arrow key to switch in­between the two display screens within the
same measurement menu.

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Input Filters

Depending on the slelected measurement functions the following sets of
lters are available:

SPL/RTA function:

Filters Applications

FLAT

Flat frequency response
(no ltering)

Overall sound pressure level, all
sound signal components are included
without weighting, required for special
applications;

A-WTD
A-weighting lter acc.
IEC 61672

Applicable for most common sound
pressure levels if level weighting following
the human ear is required.

C-WTD

C-weighting lter acc.
IEC 61672

Applicable for high sound levels if level
weighting following the human ear is
required. Verify the lter setting with the
test specications.

X-CRV

-1

Inverted X-Curve lter acc.
ISO 2969

Required for cinema installations

RLB (=Revised Low
frequency B-curve)

Broadcast Loudness lter
acc. AES Paper “Loudness
Assessment of Music and
Speech” 2004

Applicable for loudness measurement
of broadcast material. The revised B­weighted Leq measurement (=RLB)
correlates the best to the subjective
experience by humans.

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RMS/THD function:

Filters Applications

FLAT

Flat frequency response
(no ltering)

Default measurement setting.

A-WTD
A-weighting lter

Measuring residual noise of the unit
under test acc. IEC 61672 e.g. in sound
broadcasting applications.

C-WTD

C-weighting lter acc.
IEC 61672

Special applications.

HP400

Highpass 400 Hz acc. DIN
45045, -120dB/dec.

Removes any mains frequency (50/60Hz)
components from the test signal.

HP19k

Highpass 19 kHz

Removes any low frequency components
from the test signal, e.g. to measure any
20kHz pilot tone level of critical public
announcements systems.

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Setup Screen

The setup screen allows to customize basic
settings of the Acoustilyzer AL1 by the
following procedure:

• Move the cursor to the corresponding
eld and press the enter key.

• Select the required status by using the
arrow keys.

• Press the enter key to conrm.

AUTO POWER OFF denes the time the AL1 is switched OFF automatically

after the last key-press. The available settings are 3 MIN, 10 MIN, 30
MIN, 60 MIN and DISABLE. In case DISABLE is selected, the user
has to turn the unit off manually or it will run until the batteries are
discharged.

Acoustilyzer operation with MiniLINK PC Software

During the operation of the AL1 with the MiniLINK PC software, the
AL1 is powered from the PC and the following power saving functions
are disabled:- Auto Power Off - Auto Light Off. After the PC software
MiniLINK is switched off the Acoustilyzer is continuously further powered
from the PC but the power saving features are enabled again.

AUTO LIGHT OFF denes how long the backlight stays on after any key

stroke. Possible selections are 3 SEC, 10 SEC., 60 SEC. and DISABLE.
In the latter case, the backlight will stay on, until the unit is switched off.
The longer the backlight is turned on, the shorter lifetime of the batteries
will be.

LCD CONTRAST adjusts the contrast of the display. Alternatively, hold the

ESC button down and press the up/down arrow key simultaneously in
any measurement panel.

MULTIPLE SETUP allows to store up to four individual settings. To enable

the multiple setup mode, set the corresponding entry to ENABLE and
conrm. At the next time the Acoustilyzer is switched on, the user will
have to select the individual setup-ID (1, 2, 3 or 4) in the startup screen.
All parameter settings in all measurement modes are now stored under
this ID at switch off.

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Memory Menu & Battery Status Indication

All measurements can be stored into the
internal instrument memory. Each record is
saved with a le name consisting of the test
mode and a continuous running number
from 000 - 999, such as “A001_RMS_THD”
or “A002_RT60”. The running number starts
after 999 with 000 again.
You can store the test results as follows:

• STORE+BMP

Saves the numeric test results including
the graphical screenshot, indicated
by BMP (=bitmap) in the memory
overview.

• STORE

Saves the numeric test result, so
occupying less memory space.

• VIEW + DELETE

The stored measurement results are
listed in ascending order from bottom to
top, so the latest recorded measurement
is always on top of the list. The remaining
memory space is displayed in the right­upper corner of the screen.

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All screenshots marked with BMP can be
reviewed directly on the instrument.

• Select any record in the list using the
cursor.

• Press and hold the enter key.

• The recorded measurement is displayed
on the instrument screen

• The selected record is marked in the
memory menu by the full square in the
front. You can recall the marked record
at any time later by holding down the
ESC button and pressing the enter key
simultaneously.

Delete individual memory records

Each stored result can be deleted
individually from the memory.

• Select the DEL eld beside the memory
location to be deleted.

• Conrm OK within the pop up window
and press the enter key.

• The memory location is deleted from the
device memory.

Delete all memory records

The complete memory can be deleted by
selecting the eld “DEL ALL“.

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LOAD

Various Acoustilyzer functions support
the test result data loading from the
internal AL1 memory. This features is very
useful for detailed test result read out of
previously stored measurements on the
test instrument.

The following measurements support this
feature:

• SPL/RTA

• RT60

• FFT

• STI-PA

Note: Any ongoing measurement is

continuing during loading and
reading a memorized test result.

Application example using SPL/RTA:

• Select LOAD in the memory menu and
press enter.

• The possible memorized data for loading
are displayed.

• Select the test result of interest.

• Conrm the selection with the enter
key → the square symbol in front of the
selection is lled up.

• Press the ESC button (cursor jumps to
OK) and conrm with enter.

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The loaded test result is displayed on the
active AL1 screen and the abbreviation
LOD is ashing in the status bar memory
eld.

The individual band levels can be read
out, the Y-axis altered or even the Leq or
min/max. test result shown. Non-available
functionalities are not selectable.

Return back to the live mode by selecting
LIVE MODE in the memory menu of the
upper menu bar.

Low battery indication

A low battery symbol is displayed in the
“MEM” eld of the menu bar to indicate that
a change of batteries is required.

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4. Measurement Functions

Overview

Function

Test

Result

Screens

Test Features

SPL/RTA Sound Level Meter

Sound pressure level SPL, MAX/MIN SPL,
LEQ, LcPEAK

Real Time Analyzer

1/1 and 1/3 octave real time spectrum analyzer
showing SPL, MAX/MIN SPL & LEQ per band

RT60 Reverberation Time

in octave band resolution based on T20 results

Reverberation Time

detailed test results listed in seconds including
correlation factor

FFT Real-time Zoom FFT

POLARITY Polarity Test

of acoustical speaker or electrical line signals

DELAY Delay Time

Propagation delay measurement between
electrical reference and acoustical signal

RMS/THD Electrical Measurements

Level RMS, THD+N, Frequency

STI-PA Speech intelligibility

of public announcement systems in STI or CIS
test results (only visible after received STI-PA
license activation key)

Speech intelligibility

Individual LEQ and STI-PA modulation indices
of test frequency bands

CALIBRTE Calibration Menu

for external measurement microphones,
sensitivity set by default to NTI MiniSPL

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SPL/RTA - Sound Level Meter

The Acoustilyzer features a comprehensive, integrating sound level meter
with timer for single or repeated measurements. All results may be logged
into the internal memory for further investigations.

The measurements displayed on the big and small result position may be
altered between

• SPL Actual sound pressure level

• MIN SPL Minimum sound pressure level

• MAX SPL Maximum sound pressure level

• LEQ time-averaged sound pressure level

• PreLEQ LEQ of the previous timer period (only available
when timer is in repeat mode

• LcPEAK: C-weighted peak sound pressure level

The included Timer allows automatically to

• Stop the LEQ, LcPEAK and MAX/MIN SPL measurements after a
user dened time

• Reset the LEQ, LcPEAK and MAX/MIN SPL measurements after a
user dened time to start a new measurement.

Time Weighting
indicator / selector

Timer
Status

Pause Measurement

Timer, Clock

Reset Test Cycle

Period

SPL Bargraph and range
indication

Input Range
indicator arrows

Big Result

Small
Result

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Test Applications: “Timer Status” Setting

TIMER OFF

(applicable for standard measurements)
All values are recorded and monitored
continuously. The measurement timer
shows the actual testing period length.
Pressing the RESET icon sets the clock
and the test results back to zero.

TIMER SINGLE

Sound pressure level measurement with
user dened time setting.

• Set the required test cycle period.

• The clock counts back to zero. After the
dened test time is completed the clock
is ashing as”00.00.00”.

• The test results LEQ, LcPEAK and
MAX/MIN SPL are frozen.

• Changing the test cycle period setting
or pressing the RESET icon restarts the
measurement.

TIMER REPEAT

Automatically repeating measurements
with user-dened test time interval.

• Set the required test cycle period.

• The measurement timer counts back to
zero. When the test time is elapsed the
clock and the test results are reset and
a new measurement is started.

• The previously measured LEQ is
displayed as PreLEQ (very useful for
LEQ monitoring at concerts)

• Changing the test cycle period or
pressing the RESET icon restarts the
measurement.

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Pause: The LEQ, LcPEAK and MAX/MIN measurements can be paused

• Select the PAUSE symbol and press the enter key.

• The PAUSE symbol is ashing.

• The actual SPL value is continuously measured and displayed.

• Select the pause symbol and press the enter key to continue the
measurement, visible by the continuing counting clock.

Reset: Pressing the RESET icon restarts the measurement. The timer and

test results are reset.

Test Cycle Period: Applicable in SINGLE and REPEAT timer status only.

• SINGLE: Set to 10 min by default

• REPEAT: Set to 10 sec by default

Measurement Timer: Actual measurement in hours:minutes:seconds.

Big and Small Result: Two of the previous listed measurements may be

display at the same time.

Time Weighting: All SPL measurements (SPL and MAX/MIN SPL)

are time weighted measurements. Changes in the SPL level are
smoothed resulting in quicker or slower change of the displayed value.
Available time weightings, corresponding to IEC 61672, are

• SLOW (long attack- and release response time, t = 1s)

• FAST (short attack- and release response time, t = 125ms)

The time weighting for the broad band values ( ) and the RTA ( )
are always the same.

Overload

The OVL (Overload) is ashing if the
input voltage exceeded the selected
input range of the instrument. As long as
the OVL is ashing the displayed LEQ
and LcPEAK result is not accurate.

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Input Range Selector & Bargraph

In the SPL/RTA Mode the AL1 has three measurement ranges. The span
of each range depends on the sensitivity of the used microphone. For a
MiniSPL with a sensitivity of 20mV/Pa the measurement ranges are:

20 to 100 dB 40 to 120 dB 60 to 140 dB

The selected input range is displayed at the bottom of the bargraph and
may be changed by operating the range indicator arrows. The bargraph
provides an analog display of the actual sound pressure level.

Primary Indicator Range

To achieve best measurement accuracy the appropriate range

must be selected, called “primary indicator range”. Correct setting
avoids overow indications and lowers the inuence of noise on the
measurement result.

The two range indicator arrows assist the user to set the optimal range.

As soon as the indicated bargraph value is found lower than the primary
indicator range, the down arrow symbol below RNGE will start to move,
symbolizing the actual SPL measurements are inaccurate. The bargraph
range needs to be changed manually by selecting the moving left arrow
symbol and pressing the enter key.

Note: Changing the ranging resets all ongoing measurements.

By exceeding the primary indicator
range three overload arrows replacing
the big result reading.

• Select the right arrow below RNGE
and press enter to change to the next
higher bargraph range.

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SPL/RTA - Real Time Analyzer RTA

The Acoustilyzer sound level meter features the individual 1/3rd or full
octave band test results using class 0 lters. The SPL, MAX / MIN and LEQ
values are displayed per band.

Stored spectra may be averaged by using the available mathematical
functions. The MAX-MIN display is particularly helpful for characterizations
of listening areas.

Input Range
indicator arrows

Audio
Spectrum

Set
Menu

Pause Reset Cursor

Readout

X-Axis with manual
range selection

Y-Axis

The audio spectrum is displayed without interrupting any ongoing sound
level measurements, so e.g. changing from to screen will not
interrupt the ongoing sound level measurements.

Input Filter

The SPL/RTA input lter for the broad band values ( ) and the RTA ( )
may be selected independently - so e.g. a FLAT RTA is available while the
broad band values are acquired using an A weighted lter. Please note that
only various lter combinations are possible.

Note: Changing lter settings re-starts the ongoing measurement.

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Set Menu

The SET menu allows for particular
measurement settings and display options
as listed below:

RES - Resolution

Select 1/3rd octave or full (1/1) octave band
resolution by pressing the enter key.

SHOW - Test Result

The actual SPL, MAX/MIN SPL and LEQ
can be displayed per band.

The actual SPL is displayed with lled
bars.

The LEQ spectrum is displayed with framed
bars.

The MAX/MIN SPL range is displayed with
lled bars. The cursor read out shows either
the maximum, the max-min difference or
the minimum sound pressure level of the
selected band.

Simply toggle through these results with
upper & lower arrow keys:

- max. SPL

- min. SPL

- max. - min. SPL

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TWTD - Time Weighting

Applicable for the actual sound pressure
level measurement. The available response
times, corresponding to IEC 61672, are

• SLOW (long attack- and release time)

• FAST (short attack- and release time)

The time weighting for the broad band
values ( ) and the RTA view ( ) are
always the same.

HOLD - Cursor Hold

The cursors indicates the band of highest
sound pressure level. For simple read out
and traceability the cursor can remain for
1 - 9 seconds at the frequency band with
the highest level. This may e.g. support
nding of feedback frequencies.

Cursor Readout: Actual level result in the indicated frequency band.

The cursor readout displays the center frequency and the level of the
band pointed to by the arrow. The cursor automatically jumps to the
highest level band in the spectrum.

Alternatively the cursor readout may be controlled manually:

• Select the read out data eld and press the enter key.

• A frame is ashing around the data readout.

• Move the cursor and read the corresponding test results.

Pause / Reset / Input Range Indicator / TWTD - Time Weighting:

These controls are exactly the same as found on the sound level

meter screen and also effect both, the RTA and the sound level meter
measurement (e.g. pressing PAUSE in the RTA screen also pauses the
broad band LEQ, LcPEAK and MAX/MIN SPL measurements).

.

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X-Axis: Logarithmic scale xed to 20 Hz - 20kHz

Y-Axis: The scaling of the spectrum’s Y-axis (sensitivity) can be adjusted

manually.

• Select the displayed upper value of Y-axis and press the enter key.

• Use the up/down keys to scroll the displayed level along the Y-axis
and the left/right keys zoom in/out the Y-axis, e.g. to alter the display
resolution.

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SPL/RTA - Memory Functions

The SPL/RTA mode includes special memory features, such as in

SPL/RTA - Sound Level Meter

• LOGGING: records the measured parameters to the internal device
memory every time the log interval ∆t has expired (in table form).

SPL/RTA - Real Time Analyzer RTA

• LOAD: loads stored test results into the active AL1 display for
detailed read out.

• MATH: completes mathematical averaging of various stored
measurements selected from the memory.

Logging

The Acoustilyzer can record various levels over time, e.g. for monitoring
sound levels during an event for many hours, into the instrument memory.
Every time the recording interval ∆t is elapsed the results are stored and
values marked with “_dt” are reset afterwards. The logging may stop
automatically after the preset measurement time has elapsed. The results
can then be loaded to a PC and visualized as a level diagram using e.g.
Microsoft Excel.

Note: The stored results remain within the AL1 memory even in the

event of a battery failure during the recording session.

The following parameters are recorded during the logging.

LEQ Leq over the whole measurement period. The measurement

period is indicated and controlled by the measurement timer.

PreLEQ Leq of the previous measurement timer period (in timer repeat

mode only).

LEQ_dt Short time LEQ of the actual log interval ∆t. LEQ_dt values

may be combined to get the LEQ of any desired period:

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





Nn

dtLEQ

n

N

LEQ

1

10

_

10

1

log10

MIN_dt Minimum SPL value measured within the actual log interval ∆t;

time weighted value (SLOW/FAST).

MAX_dt Maximum SPL value measured within the actual log interval ∆t;

time weighted value (SLOW/FAST).

Example of an SPL/LEQ log visualized with Microsoft Excel

(without LcPEAK)

LcPeak Maximum C weighted peak sound pressure level during the

whole measurement period. The measurement period is
indicated and controlled by the measurement timer.

LcPeak_dt Maximum C weighted peak sound pressure level during the

log interval ∆t.

SPL_Act Indicates the actual SPL level measured exactly at the end of

the log interval. Please note that LEQ_dt, MIN_dt and MAX_dt
characterize an interval more accurate than this single
SPL_Act value.

33

Example of an SPL/LEQ log visualized with Microsoft Excel

(LcPEAK only)

OVER_dt A “1” indicates an overload during the log interval ∆t (so all

values tend to be measured to low).

OVER_Hold A “1” indicates an overload during the measurement period.

UNDER_dt A “1” indicates an underload during the measurement period

(so all values tend to be measured to high).

Prepare Logging

Select LOGGING from the Memory Menu.
This will bring up the Logger Setup Screen:

Setting of recording time

The maximum recording time (END) of the
sound pressure level logging depends on
the remaining memory and the selected
test interval (∆t). The logger may record
a maximum of about 580 points over a
custom dened time. The test interval (∆t)
and the total logging time can be dened by
the user in the format hh:mm:ss.

34

35

Note: During SPL/RTA logging the

instrument may be switched to
display the audio spectrum. This
is possible without interrupting
the ongoing log.

Review logging records

The measurement data are saved under
the le name “Axxx_LOGSPL”, with xxx is
a continuous running number. The detailed
records can be read out by using the
MiniLINK PC software.

LOAD - Loading Test Results

For details see the earlier chapter “Memory
Menu”.

35

MATH - Mathematical Averaging of Records

The MATH function allows to carry out
averaging of stored test results.

Application example:

• The available previously memorized
data for averaging are displayed.

• Make your selection with the enter key
→ the square symbol in front of the
selection is lled up.

• Select any number of test results for
averaging.

• Press the ESC button (cursor jumps to
OK) and conrm with enter.

The averaged test result is displayed on
the active AL1 screen and the abbreviation
MAT is ashing in the status bar memory
eld.

The individual band levels can be read out,
the Y-axis altered or even the LEQ or MIN/
MAX test result shown.

• Return back to the live mode by selecting
LIVE MODE in the memory menu.

Reverberation Time RT60

The Acoustilyzer supports reverberation time measurements in octave
band resolution according to ISO3382 with auto trigger, auto ranging and
averaging functionality.

What is Reverberation Time RT60

Reverberation time RT60 is the time required for the sound pressure level
to decrease 60 dB after the sound stimulus signal is stopped. Since ambient
noise often defeats measurements of 60dB level decrease in practice, the
RT60 results are based on T20 measurements. This requires only a 35
dB level decrease within each octave band. The RT60 test result is the
extrapolation of the measured 20 dB decay.

Test Signal

A gated pink noise signal is recommended to be used as test signal. Various
test tracks with different on/off time are included on the accompanying AL1
Test CD. Alternatively the Minirator features a pink noise signal, which has
to be physically interrupted (e.g. disconnect cable).

a. Bargraph display

Octave Bands

Start Pause Measurement

Status

Individual Octave
Band Spectrum

RT60 Upper Mark
Indicator

RT60 Lower Mark
Indicator

X-Axis,
level with
10 dBSPL
marks

Number
of Test
Results
taken for
automatic
averaging

Ranging,
initial record of
environmental
noise prior
measurment

Octave
bands scroll
63Hz - 8kHz

36

37

b. How to measure

The room under test is injected with a pink noise signal through speakers.
The sound source has to be active until balance between injected and
absorbed acoustical energy has been reached. Then the source signal has
to be stopped. The AL1 recognizes this interruption, triggers, the decay
time is measured and the RT60 test result is automatically calculated.

Please follow the RT60 test instruction below:

Ranging

• Select RANGE and press the enter key
to measure the actual sound pressure
level in the room without test signal
present.

• The SET RANGE eld pops up. Conrm
the automatic ranging by OK.

Now the RT60 upper mark indicators are
set to the minimum pink noise level needed
to successfully complete a measurement.
The lower marks indicate the environmental
noise without any test signal present.

38

39

• Start the pink noise test signal with the
appropriate on/off time according the
room under test.

Note: Use an initial low sound pressure

level (to protect your ears against
excessive sound level and hearing
damages).

• Increase the test signal level until all
individual octave band marks for the
minimum test signal level are passed.
As required an EQ can be used to push
up individual band levels.

Start RT60 measurement

• Select the START icon and press the
enter key to initiate the reverberation
time measurement.

• The status indication switches to
ARMED.

• Complete several test cycles so an
averaged test result is calculated.

• The individual octave band sound
pressure level increases above the
upper marks.

• Upon the sound pressure level has fallen
below the lower marks in each individual
octave band the RT60 is calculated.

• Switch off the test signal.

Conrmation marks are displayed for
successful octave band reverberation time
measurements.

39

Test result read out

The detailed RT60 test results in
x.xx seconds are listed in the RT60 test
result screen. Select the detailed test result
read out screen by

• Using the screen menu

• Alternatively press the ESC and the left
or right arrow key simultaneously.

Note: During the ongoing RT60

measurement the memory menu
is not available.

c. RT60 Test Result Read Out

Test Result
in seconds

Correlation Factor in %
or Measurement Uncertainty

Relative Test
Result, displayed as
bargraph

Test Result
Selection

Number of
continuously
taken test
results

Delete selected
Test Result

Start Pause

Octave
bands scroll
63Hz - 8kHz

Test Result Selection: The RT60 measurement function enables

consecutive reverberation time measurements within one test
sequence. Automatically an averaged test result of all measurements
is calculated.

40

41

Toggle with the left and right AL1 cursor keys through the individual test
result cycles and you can nd the following:

Last test result

The test result of the last test cycle is
displayed at selection LAST.
You can use the upper and lower AL1
cursor keys to display the 63 Hz or 8 kHz
octave band test result additionaly.

Single test cycle results

The individual single test results are
marked with CYC xx, whereby xx is a
continuous running number.

Averaged test result

By selecting AVRG the averaged test
results of all taken measurements
are calculated and displayed. The
correlation factor is replaced by the
measurement uncertainty factor in %.

Relative Test Result, displayed as bargraph: To simplify the data read

out the reverberation time is additionally displayed as bargraph, whereby
the octave band with the longest measured reverberation time is shown
with a bargraph of maximum length. The other octave band test results
are displayed relative to the longest time.

Correlation
Factor in %

Correlation Factor in %

(applicable for single test results)
This factor will be 100% for perfect linear
sound pressure level decay after the
source is switched off. Deviations from
linearity result in lower correlation values.
(typically 80 - 100% at reliable RT60 test
results).

41

Uncertainty
Factor in %

Uncertainty Factor in %

(applicable for averaged test result)
Based on at least three individual
test results, the uncertainty factors
are calculated. This factor equals the
statistical test result accuracy based on
the randomly created pink noise test signal
(typically 0 - 15% at reliable RT60 test
results). Please see the standard ISO 3382
for details.

Error Indications

Delete single
test results

Various error indications display non
successful RT60 measurements, These
can be deleted individually. Non-valid results
are excluded from average calculations.

• LOW LEVL

This is the abbreviation of “low test
signal level” during the measurement

→ Increase the test signal level and
verify that all levels are exceeding the
upper marks

→ Use a corresponding RT60 test signal
with longer on/off times, so the lower
level mark can be reached

• CORR<70%

The correlation factor is lower than 70%
indicating a unreliable measurement
result.

• T>18S

The measured reverberation time
exceeds the time limit of 18 seconds,
e.g. caused by a not suitable ranging or
environmental noise.

In this case repeat the ranging and start
the measurement again.

42

43

FFT Analysis

The Acoustilyzer includes an extremely fast, real-time Zoom FFT with
resolutions up to 0.7Hz over the entire frequency range. The display shows
93 bins simultaneously.

The FFT measurement is the ideal tool for visualization of comb lters and
narrow band effects. It allows a detailed investigation of the frequency
response of audio systems.

FFT Audio
Spectrum

Set
Menu

Pause Cursor

Readout

Start Frequency
of Display

Y-Axis

End Frequency
of Display

Size of displayed
Frequency Range

Set Menu

The SET menu allows the setting of
measurement- and display options as
follows:

43

Range - AL1 Input Ranging

The Acoustilyzer has different input
ranges.

• The range is set automatically at
entering the FFT mode

• Carry out the input ranging if any clipping
or high noise occurs

SHOW - Test Result

Select the display of actual SPL or averaged
sound pressure level (=LEQ). The LEQ
measurement can be reset by executing
the range setting or at the new selection of
SHOW: LEQ.

HOLD - Cursor Hold

The cursor indicates the frequency of high­est sound pressure level. For simple read
out and traceability the cursor can remain for
1 - 9 seconds at the frequency with the
highest level.

Pause: The FFT measurement may be frozen for a user dened time.

• Select the PAUSE symbol and press the enter key.

• The PAUSE symbol is ashing.

• Select the PAUSE symbol and press the enter key to continue the
measurement.

Cursor Readout: Actual level result of the indicated frequency bin.

The cursor readout displays the bin-frequency and the corresponding
level. The cursor automatically jumps to the highest level in the spectrum.
Alternatively the cursor readout may be controlled manually:

• Select the read out data eld and press the enter key.

• A frame is ashing around the data readout.

• Move the cursor and read the corresponding test results.

44

45

X-Axis: Linear scale, showing from left to right the start frequency, the

frequency range and the end frequency by 92 bins with zooming
functionality.

Y-Axis: The scaling of the Y-axis can be adjusted manually.

• Select the displayed upper value of Y-axis and press the enter key.

• Use the up/down keys to scroll the displayed level along the Y-axis
and the left/right keys zoom in/out the Y-axis, e.g. to alter the display
resolution.

How to measure:

• Select the FFT function. The cursor
read out shows the maximum level
automatically.

• Select the cursor read out eld and
conrm with enter. A frame is ashing
around the read out data.

• Read out other values using the left or
right arrow keys.

Zoom in/out to cursor position

• Select the cursor read out eld.

• Use the lower arrow key to zoom in up
to a 0.7 Hz frequency resolution and the
upper arrow key to zoom out.

• Move the x-axis by left/right key press.

Zoom in/out with quick X-axis shifting

• Select the x-axis frequency range eld

• The zoom in/out functionality refers to
the displayed center frequency.

• Use the left/right arrow key for quick left/
right shifting of the x-axis.

45

Application: FFT and White Noise

White noise is most often used as test signal when measuring the
performance of acoustical systems. The FFT shows a at spectrum with
this input signal. Feeding white noise into an electro acoustic system and
measuring the FFT using a measurement microphone shows the frequency
response of the system with very high resolution.

Please note that the frequency response seen is most often a combination
of two effects:

a) The “real” frequency response of the electronics and speakers
b) Interference effects (resulting in comb ltering)

With a high resolution FFT interference effects can easily be seen - while
they are nearly impossible to notice on a 1/3 octave resolution RTA.

The Zoom FFT of the AL1 allows to “Zoom In” at any frequency point to a
resolution of up to 0.73 Hz.

4 x zoom →
level reduces
by 6 dB

White Noise and Zooming

The energy of “White Noise” is equally
distributed over the linear frequency axis.
Let’s assume we have a White Noise signal
with a level of 0 dB measured using a
bandwidth of 20 kHz.

What happens if we decrease the
measurement bandwidth to 10 kHz?

→ We only measure one half of the energy –
resulting in a level of -3 dB (10*log10(0.5)).

This is exactly what happens if we
“Zoom In” using an FFT. Every time we
“Zoom In” the measurement bandwidth is
halved – resulting in a 3 dB lower level in
every bin.

46

47

Polarity Test

The polarity test function detects the correct cable and speaker polarity in
combination with the Minirator MR1 polarity test signal. The Acoustilyzer
provides the following test congurations:

a. Speaker Polarity Test

• Feed the speaker system with the
polarity test signal of the Minirator.

• Adjust the level (at MR1 or amplier) so
the test signal is good to hear.

Acoustilyzer settings:

• IN:MIC (INT), using the internal mic of
the Acoustilyzer AL1

• IN:XLR/RCA, using an external mic,
such as the MiniSPL

Choose the polarity test frequency range:

• FULL/MID, for wide band speaker tests

• WOOFER, for woofer tests

Notes:

• Please note the polarity testing is a simplied measurement of a
very complex signal phasing. Drivers, speakers and cross-overs
cause severe phase shifts of the audio signal.

• The polarity of various speakers within the same cabinet can
be different. This is not a problem nor caused by bad speaker
design.

• Polarity testing is useful for checking the correct wiring of similar
speaker systems.

47

b. Cable Polarity Test

Use the polarity test signal of the Minirator to
feed the cable under test. The Acoustilyzer
analyzes the signal polarity at the other end
of the cable.

Acoustilyzer settings:

• IN: XLR/RCA,

• Mode: Cable

The following problems may be detected quickly and easily:

• Wrong polarity, caused by wrong or defective wiring inside the cable

• Cable problems, unsymmetrical signals, displayed with the balance
indicator, can help to detect various cable problems, such as

“2UBAL–” indicates an audio signal only on pin 2 of the symmetrical

XLR cable → no signal at pin 3.

“-UBAL3” indicates an audio signal only on pin 3 of the symmetrical

XLR cable → no signal at pin 2.

The balance indicator out of center leads to other cable problems as
explained in detail in the NTI application note “Signal Balance“ (available
for download at the NTI website).

The level measurement is very useful for applications, such as testing of
multicore cables (see the NTI website for application notes).

48

49

Delay Time

The setting of the acoustics propagation delay time from speaker to speaker
in e.g. churches or auditoriums, is required so the listening public notices
the acoustics of the speaking person from his actual position and not from
the side or rear speaker installed.

The Acoustilyzer measures the delay time of the acoustical speaker signal
(using the built-in microphone) against the electrical line reference signal
(connected at RCA or XLR input). As delay time test signal a designated
chirp, provided on the AL1 Test CD, has to be used.

Converted
Delay Time in
meter/feet

Delay Time
Memory

Automatically calculated Delay Time
Store - Actual

Start Synchronization

Synchronization Time Bar
100% = 100 seconds

Actual
measured
Delay Time
to Electrical
Reference
Signal

Status Indication

Synchronization: The automatic synchronization allows delay time

measurements without any connected electrical reference signal for
100 seconds and displays the time remaining for the next required
synchronization.

Manual Synchronization:

Initiate a manual synchronization by selecting SYNC.

49

How to measure

Note: Please de-activate any shock

protection of the CD-player since
this might cause incorrect test
results!

Test preparations

• Switch on the acoustical delay time
measurement signal, available on the
AL1 Test CD.

• Connect the electrical signal, e.g. from
the CD player, to the AL1 RCA or XLR
input.

• Wait until the Acoustilyzer synchronizes
to the incoming delay time test chirp and
the synchronization time bar lls up to
100%.

The delay time measurement is conducted
between the synchronized electrical input
signal and the built-in microphone of the
Acoustilyzer.

Measure Reference Speaker

• Select a speaker as reference speaker,
called speaker A, e.g. the speaker most
in front of the delay line.

• Position yourself in the sound eld of
the next speaker under test, e.g. called
speaker B, to measure the delay time
compared to the reference speaker A.

Note: Do not position the Acoustilyzer to

close to reecting surfaces, such
as walls or oors. The reections
may int erfere any accurate
measurements.

50

51

Change
[m][°C] ↔ [feet][°F]

• Enable the test signal at the reference
speaker A. All other speakers shall be
switched off.

• The delay time of the acoustical signal in
reference to the electrical input signal is
displayed in milli-seconds. The distance
results in meter/feet are displayed for
easy verication of the test results. The
readings are based on 330 m/s sound
speed at 0°C / 32°F.

• Set the actual environment temperature,
so the distance is displayed correctly.

Store reference

• Select STORE to memorize this test
result as reference record for further
delay time measurements.

• The stored reference delay time is
shown in the delay time memory eld.

Measure Propagation Time at Speaker

• Enable the test signal at the speaker B.
All other speakers shall be switched off.

• The acoustical delay time of speaker B
in reference to the electrical input signal
is displayed as big test result.

Automatic Time Difference Calculation

• The delay time difference is automatically
calculated and shown in the upper small
STO-ACT (stored - actual) eld.
The automatic difference calculation
simplies the verication of delay line
arrangements, e.g. used in larger halls
or auditoriums.

51

Electrical Measurements - RMS/THD

The Acoustilyzer supports basic electrical measurement functions,
such as

• Level RMS, reects the absolute level of the line input signal.

• THD+N, Total Harmonic Distortion plus Noise, besides checking the
linear purity of a sine signal - e.g. measuring the amount of harmonic
distortions - this mode is particularly suited to get a quick idea whether
unwanted interferences like hum are present.

Distortion
THD+N

Signal
Frequency

Signal Balance
Indicator

Level RMS
Result and Unit

Level RMS: The units dBu, dBV, dBSPL and V are selectable.

Distortion THD+N: The distortion measurement, expressed in dB or in %,

is carried out in the bandwidth 10 Hz - 20 kHz.

52

53

Signal Balance shows the matching deviation of the incoming signal

between pin 2 and pin 3 in percent (%). The arrow position indicates the
following:

• Arrow in center, the input signal is balanced.

• Arrow out of center, linear indication of a balancing problem, e.g.
arrow moves left nearer to the number 2 shows the signal level on
pin 2 is higher than on pin 3.

• Arrow at left or right end, the signal balance error is 33% or higher.
33% equals a difference in the signal level of 6 dB.

• 2UBAL-, indicates an audio signal only on pin 2 of the symmetrical
XLR cable → no signal at pin 3.

• -UBAL3, indicates an audio signal only on pin 3 of the symmetrical
XLR cable → no signal at pin 2.

Notes:

• The Adapter -20dB shall be applied for balanced input levels
higher than +20 dBu (see Accessories for details).

• The THD+N results are calculated using a measuring bandwidth
of 10 Hz - 20 kHz.

53

Speech Intelligibility STI-PA (optional)

The speech intelligibility measurement STI-PA is an optional sales package
for the Acoustilyzer AL1. Ask your local representative for purchasing
details.

The STI-PA analyzer option allows reliable measurement of the speech
transmission index within 15 seconds. Besides the single value STI or CIS
test result, a detailed view of the modulation indices and individual band
level results is provided. The STI-PA analyzer fullls the latest 2003 IEC
60268-16 standard and is a TNO veried algorithm (dutch STI-PA research
institute).
Find more information about speech intelligibility basics and the historical
developments in the APPENDIX to this user manual.

a. STI-PA Measurement Screen

Actuall
Sound
Pressure
Level

Measurement Progress Bar
(0..15 seconds)

Analogue STI-PA Bargraph

STI-PA
Test
Result

Start
Measurement

Measurement
Status
Indication

STI-PA Test Result: Single value speech transmission index result in

STI (speech transmission index) or CIS (common intelligibility scale),
whereby CIS is calculated as CIS = 1 + log STI.

Sound Pressure Level: Shows actual SPL value in dBAS, including

A-weighting and Slow time weighting.

54

55

b. How to measure

• Select the STI-PA function.

• Monitor the actual sound pressure level
of your environment on the Acoustilyzer
display.

Preconditions:

• To avoid measurement failures the
STI-PA test signal level should be
min. 60 dBSPL.

• The STI-PA measurement should be
carried out at emergency conditions
(same sound pressure level and all
components are activated).

• No impulsive noise events should occur
during the 15 seconds measurement
time.

NOTE: Even intermediate noise may

affect the STI-PA test result.

Signal Source:

The NTI TalkBox can simulate a human
talker, enabling the measurement of the
complete system including the microphone
part (directivity, room characteristics, ...).
Place the NTI TalkBox at the typical human
speaker position.

A CD Player with the NTI CD “STI-PA
V1.1” or higher can be used for electrical
signal injection for system tests without the
microphone part.

55

• Start the STI-PA test signal.

• Set the acoustical sound pressure level
of the PA system according the typical
emergency condition requirements, e.g.
85 dBAS.

• Press START on the AL1 menu to
initiate the measurement. Near the
measurement microphone is no
speaking or additional noise allowed
during the measurement.

A STI-PA measurement takes 15 seconds.
The elapsed test time is visible as blank part
in the upper measurement progress bar.

The test result tendency is shown on the
below STI-PA bargraph, marked with BAD,
PR (poor), FR (fair), GD (good) and EXLT
(excellent).

After the 15 seconds test cycle time the
Measurement Status Indication switches to
FINISHED and the nal STI-PA test result
is displayed.

On the bargraph below the quality of the
speech intelligibility test result is displayed
as

• BAD 0.00 - 0.30 STI

• PR (poor) 0.30 - 0.45 STI

• FR (fair) 0.45 - 0.60 STI

• GD (good) 0.60 - 0.75 STI

• EXLT (excellent) 0.75 - 1.00 STI

56

57

The detailed test result view of the
modulation indices and individual band
level results is provided on the second
STI-PA measurement screen.

c. Detailed Test Result Read Out

STI-PA
Octave Bands

Individual Octave
Band LEQ Level

STI-PA Modulation
Index 2

STI-PA Modulation
Index 1

Error
Detection

STI-PA Modulation Index 1 & 2:
For high speech intelligibility it is mandatory that the integrity of the
transmitted voice signal modulations are preserved. Therefore STI-PA is
based on measuring the MTF (Modulation Transfer Function). This function
quanties the degree to which the voice modulations are preserved in
individual octave bands. STI-PA determines the MTF by analyzing all seven
frequency bands, whereby each band is modulated with two frequencies,
so resulting in the modulation index 1 and index 2

57

d. STI-PA Post Processing

Measuring the speech intelligibility with realistic environmental noise is
often not applicable, e.g. in railway stations these measurements might
not be carried out during peak hours with highest background noise level.
In practice the STI-PA measurement will be much rather taken during the
night as less persons getting disturbed by the played test signal.

For such special applications the STI-PA result taken at quiet conditions
can be post-processed with the worst case noise spectrum, predicting the
expected speech intelligibility during these worst case conditions.

The Microsoft Excel program “STI-PA_PostProcessing.xlt” combines
“noiseless” recorded STI-PA results with environmental noise spectra
and predicts the resulting STI value. STI-PA and RTA results (1/3 and 1/1
octave) recorded and stored with the Acoustilyzer may be imported (use
the MiniLINK Software to transfer these results from the AL1 to the PC).

“STI-PA_PostProcessing.xlt” is available

• For download at “http://www.nt-instruments.com/acoustilyzer”

• On the CD “MiniLINK - PC Software”

Note: At opening the post processing sheet all macros have to be

activated.

58

59

e. STI-PA Error Detection

The Acoustilyzer STI-PA measurement function has a built in error detection
which helps you identifying faulty measurements. The error detection
checks the following parameters:

• Invalid modulation indices (MF1 or MF2 > 1.3)

• Irregularities during ongoing measurements

Both parameters depend on the amount of impulsive environmental noise.
Impulsive environmental noise inuences any STI-PA measurement and
makes the values inaccurate.

If the error detection nds any problem the
common STI-PA test result is displayed
interrupted with the ashing “?.??” question
marks.

This error indication might be caused either
by

• Missing test signal level

• Impulsive background noise events

Detailed test result screen

The octave bands detected with
irregularities, are marked with a question
mark (?).

Recommendation

If the error detection nds any faults NTI
recommends to repeat the measurement
and to compare the STI test result with the
previous ones.

59

f. STI-PA Measurement Hints

1. Any background noise has to be sufciently static during the
measurement, e.g. pink noise fullls this requirement.

2. Verify the environmental conditions prior testing. Complete STI-PA
measurements without any test signal. The results shall be < 0.20 STI.

3. Impulsive background noise during the measurement, such as speech,
causes severe measurement errors. The STI-PA result is usually too
high.

4. In case such impulsive noise can not be prevented, the measurements
might be shifted e.g. to night time, and afterwards corrected with the
averaged daily background noise, using external post processing.

5. Any CD-Players used to reproduce the STI-PA test signal have to be
accurate as only limited time-shifts (+/- 200 ppm) are allowed to
ensure reliable STI-PA test results. Pitch control and shock protection
shall be disabled. NTI recommends using professional players only.

You may verify the time shift of your CD-Player with a 9 kHz test signal:

• Generate a 9000 Hz sinus signal using the NTI Wavelegenerator

(available for download at “www.nt-instruments.com/downloads”)
and copy this on a CD

• Insert this CD into the CD player and play the 9 kHz test signal

• Connect the Acoustilyzer to the audio output directly and measure

the signal frequency in the RMS/THD mode, the displayed frequency
shall be in the range from 8998 to 9002 Hz (the last digit equals
111 ppm at 9 kHz)

6. The STI-PA test signals of other test system manufacturers may sound
similar but are not compatible. Only the NTI STI-PA test signal CD V1.1
or higher shall be used in combination with the Acoustilyzer AL1.

7. STI-PA measurement of alarm systems shall be carried out at
emergency conditions (same sound pressure level and all components
are activated).

8. At locations undergoing different circumstances, e.g. public areas with
few people or crowded areas, the worst case STI-PA results has to be
measured.

9. Select typical locations, such as positioning the microphone
at 1 - 1.2 meters above ground in sitting areas or 1.5 - 1.8 meters
in standing areas (typical measurement positions are normaly not
directly in front of the speakers)

60

61

10. The person taking the measurements should be out of the acoustic
eld, so not affecting the measurement results. For this purpose
the measurement microphone can be mounted on a mic stand and
connected electrically (using an extension audio cable) to the AL1.

11. Low STI-PA readings can be caused by

• Excessive sound reverberation, echoes or reections

• Poor speaker directivity or speaker coverage

• Speaker power setting not in order (e.g. low signal-to-noise ratio)

Please see the NTI website or Appendix for further information.

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Calibration

In order to obtain correct measurement results the microphone sensitivity
connected to the AL1 must be set and calibrated accordingly. The microphone
sensitivity is set by default to the NTI MiniSPL measurement microphone factory
adjustment 20mV/Pa. MiniSPL is the standard measurement microphone
for the Acoustilyzer AL1.Together they are forming a comprehensive class
2 acoustics analyzer.

Alternatively to the MiniSPL the NTI M2010 class 1 frequency response
microphone can be used for highly accurate class 1 measurements.

Microphone
Sensitivity

Microphone Balance Indicator,
arrow has to be centered to verify
the balanced mic input singal

Default
Factory Setting

Manual Calibration with
external microphone calibrator

The following three calibration modes are available:

DEFAULT

All MiniSPL microphones are factory
calibrated to a sensitivity of 20.0 mV/Pa.
Reset to default setting by:

• Select DEFAULT

• Press the enter key

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63

CALIBRATE

The sensitivity may be adjusted with an
external calibrator.

• Select the dBSPL value eld (default
= 114 dBSPL), press the enter key
and adjust the sound pressure level
as provided by your calibrator. Use up/
down keys for 1.0 dB

SPL

steps and left/

right keys for 0.1 dB

SPL

steps. The level

range 80 - 140 dB

SPL

is supported.

• Conrm the setting with the enter key.

• Produce the specic reference signal
with the calibrator onto the microphone.

• Press enter to execute the calibration,
whilst the reference signal of the
calibrator is still present.

• The frame WORKING ... followed by
the frame CALIBRATION FINISHED!
is shown centered on the calibration
screen.

• The new sensitivity is shown in mV/Pa.

• Enter the SPL/RTA mode and check the
calibration by applying the reference
signal again to the attached microphone.
The sound pressure level of the
calibrator shall be shown to conrm the
calibration is carried out in good order.

In case of calibration problems various error
indications may be displayed to inform the
user about problems, such as caused by

• to low or to high input level.

• the calculated sensitivity is out of the
range 2 - 80 mV/Pa.

63

Manual sensitivity setting

• Select the sensitivity value eld,

• Press enter and adjust the sensitivity
using the up/down keys for 1.0 mV/Pa
steps and left/right keys for 0.1 mV/Pa
steps. The setting range 2 - 80 mV/Pa is
supported.

• Press enter to conrm the setting.

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65

5. MiniLINK PC Software

The MiniLINK PC software enables the transfer of stored measurements
from the Acoustilyzer AL1 to the PC. Additionally the online data logging
from the AL1 directly to the PC is supported

Installation

a. Switch on the PC with Windows operating system (MiniLINK supports

Windows 98 SE, 2000, ME and XP)

b. Insert the enclosed MiniLINK CD into the CD drive.

c. The MiniLINK software installation starts automatically. Follow the

instructions on the screen.

If the CD auto-start is disabled on the PC, follow the instructions below:

• Click on “Start → Run“ at the windows taskbar.

• Type “d:\setup“ (assuming “d“ is the letter of the CD drive)

• Conrm with “ok“

After completing the software installation, the MiniLINK CD shall remain

in the CD drive for the next step.

Note: If the MiniLINK PC software has been previously installed

on the PC, the old version will automatically be removed.
After removing you need to run the setup program again to
install the new software.

d. Use the attached USB cable to connect the test instrument to the PC.

Windows recognizes the new hardware component automatically and
starts the hardware installation assistant.

Follow the instructions of the installation assistant. Please select the CD

drive with the inserted MiniLINK CD as source for the USB driver when
asked by the installation assistant.

In case the warning messages “Digital signature not found”, “Do not

install driver”, “not certied driver” or similar come up: Don’t listen to
Microsoft, listen to us and continue with the installation.

65

Start the MiniLINK PC Software

After the successful driver installation, the MiniLINK software can be
started.

• To start the software follow the windows path “Start → Program →
MiniLINK”.

• The analyzer switches on automatically and the following screen is
displayed on the monitor:

The test instrument is powered by the USB interface and therefore switches
on by itself. During the operation with the connected USB interface the
batteries should not be removed from the device.

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67

Free Registration of your Test Instrument

The Acoustilyzer includes additional “bonus features“, enabled after the
registration of the test instrument at the NTI web site.

Overview of available bonus features:

Instrument Function Display

AL1 Customized start-up screen

Online registration:

After the startup, the MiniLINK software automatically suggests the
registration of non-registered connected instruments. The test instrument
needs to be connected to the PC. Proceed with the automatic registration
or alternatively select the MiniLINK menu “Help → Register“.

Ofine registration:

Register your device at “http://registration.nti-audio.com/Registration.php”.
Key in your details and the serial number of the device. Read out the
instrument serial number from your device by starting the instrument and
keeping any button pressed. The start up screen remains displayed. The
serial number starts with three letters (such as ANK675A0A2).

After successfully registering your device, you will receive an e-mail
with your registration key within a few minutes. Please insert this key in
the MiniLINK menu “Help → Register“. The test instrument needs to be
connected to the PC.

67

Read Out of Stored Test Results

The analyzer memory is automatically transferred to the PC and visualized
with small screenshots at the MiniLINK memory window.

Note: The MiniLINK memory window remains empty when no test

results are stored within the instrument. Otherwise, use the PC
mouse to click onto the “AL1 Memory“ tab to initiate and update
the data memory window.

The test instrument display at the PC is synchronized to the actual LCD
screen display of the connected audio analyzer. The title bar shows the
serial number and rmware version of the test instrument.

Synchronized Display

MiniLINK PC

Software Release

Version

Firmware of

connected audio

analyzer

Serial Number of

connected audio

analyzer

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69

Visualizing the Test Results

All stored screenshots are shown in the MiniLINK tab “AL1 Memory“.

Stored screenshot incl. numerical results

Stored data without screenshot

Arrows indicating additional
numerical test results are stored
together with this screenshot

Big view of screenshots

A double click on the screenshot will enlarge
this screenshot. In this mode the menu
allows printing, saving or copying of the
screenshot or the numerical test results.

Any available numeric table is listed below
the big view screenshot.

69

Copying of Test Results and Screenshots

The displayed screenshots can directly be
copied into reports for documentation.

• Select the menu “Edit → Copy Bitmap”
to choose the graphics or select the
menu “Edit → Copy Text” to choose the
numerical measurement data

• Insert the clipboard into the reporting
document with “Ctrl + V”, such as
Excel, ...

Alternatively import the stored “*.txt” le,
including the numerical measurement data,
e.g. to Microsoft Excel by using the Excel
import assistant.

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71

Example: Display of SPL/RTA test results

The SPL/RTA sound pressure level measurement provides the following
test results:

• Test conguration

• Time, relative to logging start

• All relevant sound level parameters
(please refer to section “SPL/RTA - Memory Functions” for details).

71

Save Test Results & Screenshots

The displayed screenshots can be saved as bitmap les (*.bmp) to the PC’s
hard drive. Any available numeric test data will be saved as text les (*.txt).
The le names are the rst six (6) digits of the device serial number and the
screenshots name.

For example the screenshot “A011_RT60” recorded e.g. with an Acoustilyzer
S/N ANK675 is saved as

• “ANK675_A011_RT60.bmp”

• “ANK675_A011_RT60.txt”

This enables to store various test results of more audio analyzers on the
same PC. Save the stored test results as follows:

• Select the screenshots to be saved in the memory eld.

• Press the SAVE button or select in the menu “File → SAVE“.

• The following menu below will be displayed. Select the conguration
and press SAVE.

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When saving the screenshots to the PC the same memorized values can
be deleted at the test instrument automatically. Just select in the above
displayed menu “Delete les in instrument memory after save” to empty the
test instrument memory simultaneously.

Delete Test Results of Analyzer Memory

The memorized test results in the test instrument can be deleted as
follows:

• Directly in the test instrument memory overview

• Select the screenshot in the MiniLINK memory screen and press
DEL on the PC keyboard or using the delete function of the MiniLINK
memory menu

• Selecting the delete function when saving the screenshots/test
results to the PC

Test Result Logging at the PC

MiniLINK also allows the continuous logging of the Acoustilyzer test results
online in customer dened time intervals. This test data is saved into the
default log le software directly. At the end of the logging process, press
the “SAVE” button to save and the data are saved under the le name e.g.
“ANK675_PcLog_Level SPL”.

The logging function is ideally suited for long term monitoring or
troubleshooting, e.g. in repair or broadcast applications.

73

icon for direct copying of

present screenshot

To log online results, please:

• Select the requested measurement function at the test instrument

• Select the “Logging“ screen in the MiniLINK PC Software menu

• Select the required log time interval

• Press the “START” button to start the test result logging

• Press the “STOP” button to end the logging process

• Press the “SAVE” button to save the record to le

Additionally the present screenshot displayed on the MiniLINK PC software
can be directly copied to le by pressing the marked icon with the mouse
button. Paste the screenshot into any les by pressing “CTRL + V”.

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75

Remote Test Instrument Control with the PC

MiniLINK supports the remote control of the analyzer from a PC. Just click
on the displayed test instrument and all keys can be operated with the
below listed keys at the PC keyboard or using the mouse.

arrow keys & enter

Light: Ctrl + L

ESC

On/Off: Ctrl + P

“Shift ←” or “shift →” or the above indicated areas allow to change the
screen selection of the enabled measurement function.

Click into these areas
to change the screen
selection
(e.g. SPL ↔ RTA)

75

MiniLINK Tools

The MiniLINK PC software includes many useful tools as follows:

• LCD Fullscreen

• Update Firmware

• Crossgrade Firmware

• StartUp Screen

76

77

LCD Fullscreen

The actual test instrument display can be shown on the PC monitor in a full
screen mode.

To enter the full screen mode:

• Select the menu “Tools → FullScreen“ at MiniLINK
or click onto the symbol.

To exit the full screen mode:

• Press the “Q” button on the PC keyboard
or simply click into the screen with your PC mouse.

icon for large
screen display

77

Firmware Update

NTI provides free updates of the test instrument rmware and the MiniLINK
PC software at the NTI website “www.nt-instruments.com”.

To check out any available online updates, follow these instructions:

• Connect your PC to the web & start the MiniLINK PC software

• Connect the instrument with the USB cable to the PC

• Select the menu “Help → Look for Updates“ at MiniLINK

• Follow the download instructions

Alternatively you can check for any new rmware and software releases at
the web site “http://registration.nti-audio.com/VersionCheck.php”.

• Select the menu “Tools → Update Firmware“ at MiniLINK

Select the new rmware version in the displayed screen below:

for Minilyzer ML1:
ML1dA_V3.xx.bin

for Acoustilyzer:
AL1dA_A1.xx.bin

applicable rmware for
the connected device

After conrming the selected device rmware, the test instrument rmware
is updated automatically.

Note: In case of any problems during the rmware upgrade, such

as power failure, etc., the upgrade procedure can be repeated
anytime.

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79

Firmware Crossgrade

The Acoustilyzer AL1 and the Minilyzer are based on the same hardware
platform with different specic rmware installed. The available crossgrade
packages allow to install the ML1 rmware into the AL1 or to install the AL1
rmware into the ML1.

• Select the menu “Tools → Crossgrade Firmware“ at MiniLINK

Select the displayed rmware version in the screen below:

for Minilyzer ML1:
AL1dA_A1.xx.bin

for Acoustilyzer:
ML1dA_V3.xx.bin

applicable rmware for
the connected device

After conrming the selected device rmware, the crossgrade rmware
is installed automatically within several seconds. The instrument displays
UPDATING FIRMWARE.

Note: The rmware crossgrade deletes the internal device memory.

79

Customizing the Startup Screen

The MiniLINK PC software supports the transfer of customized start-up
screens to the test instruments. The personally dened start-up screen will
be displayed instead of the factory logo every time the test instrument is
switched on.

• Start the MiniLINK PC software

• Connect the instrument with the USB cable to the PC

• Select the menu “Tools → StartupScreen“ at MiniLINK

The following screen is displayed on the monitor:

The panel “Set Startup Screen” displays a sample default factory startup
screen. The white center area (100 x 32 pixels) can be customized by the
user. The remaining top & bottom gray area is xed and cannot be altered.

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81

Guideline to dene the new start-up screen:

• Use a pre-dened picture. The MiniLINK PC software will convert it
to a 100x32 pixels black & white picture automatically. The following
le types can be used as start-up screens: *.pcx;*.bmp;*.dic;*.rle;*.ico;
*.wmf.

• Alternatively create a new start-up screen yourself using any picture /
paint programs, such as “Microsoft Paint”. Set the le size to 100x32
pixel and insert any text or graphics for the start-up screen. Save the le
as “*.bmp* format.

• Press the button “Load Image” to select the le containing the new start
up screen.

• The start-up screen preview is displayed on the PC monitor.

• Press the button “Send to Device” to transfer the le to the device

• The audio analyzer is switching off and on automatically, so you can
check out the new start-up screen by yourself immediately.

Sample start-up screens:

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Activate Options

The activate options menu is required for

• Activation of AL1 functionalities on your Minilyzer ML1 or the
ML1 functionalities on your Acoustilyzer with the crossgrade
package

• Activation of STI-PA measurement functionalities on the instrument

To activate one of the above functionalities

• Select the menu “Help → Activate Options“ at MiniLINK

• The following menu will be displayed

Follow the online activation instructions. Additionally detailed instructions
are enclosed with the license number within the individual product
package.

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83

6. Troubleshooting

Numeric data import of “*.txt” les to Excel

Problem:
The numbers are recognized as text only at the import of numeric test
results to e.g. Microsoft Excel, so you cannot create tables or use the data
for further calculations.

Solution:
The MiniLINK data les use the “.” as decimal separator. Therefore please
set the decimal separator to “.” at the import procedure of these numeric
test results into e.g. Microsoft Excel.
Alternatively you can use copy → paste in the big view mode, select
the menu “Edit → Copy Text” and paste the data into an open Excel
document.

Factory Reset

To reset the instrument back to factory settings proceed as follows:

• Switch the unit off

• Press the ESC button and the On button at the same time for a few
seconds

• The start-up screens shows up, reading in the bottom line “LOADING
DEFAULT SETUP”

The instrument is now reset to factory conditions.

83

7. Accessories

MiniSPL

The MiniSPL is the perfect accessory for
acoustical measurements. Together with
the Acoustilyzer AL1 a comprehensive
integrating sound level meter is formed.

The MiniSPL is a self contained omni
directional 1/2" measuring microphone with
built in impedance converter, pre-amplier
and power supply. It is battery powered and
the XLR-output is balanced. The MiniSPL
is classied as class 2 in accordance with
IEC 61672 and is factory adjusted to a
sensitivity of 20 mV/Pa.

STI-PA Measurement Option

The STI-PA analyzer option allows the
reliable measurement of the speech
transmission index according to the latest
IEC standards within 15 sec. Besides the
single value STI or CIS test result, a detailed
view of the modulation indices and individual
band level results is provided.

NTI TalkBox

The TalkBox is the missing link for the
complete evaluation of speech intelligibility
in emergency life & safety announcement
systems, from the talker’s microphone
to the listener’s ear. The NTI TalkBox
presents the standardized voice-like
acoustical signal emission simulating a
human talker according to IEC 60268-16,
combined with a TNO certied speech
intelligibility signal at standardized levels.

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85

ML1 - AL1 Crossgrade

The ML1 - AL1 Crossgrade package enables
to load the Minilyzer rmware onto your
instrument, providing test functionalities,
such as

• vu-PPM

• Balance

• THD 2nd - 5th
harmonics

• Scope

• Frequency
Sweep

• Time Sweep

• Induction Loop
Mode

Adapter -20dB

The Adapter -20dB may be applied for
balanced input levels higher than +20 dBu.
This passive adapter extends the balanced
input range of your Minilyzer/Acoustilyzer
up to +40 dBu. The adapter is supplied with
pin1-fuse for safe operation in combination
with the USB interface MiniLINK.

Pouch

The soft pouch protects your Minstrument
against shocks, dust and water. With its
convenient belt-clip you can keep your
Minstrument close to you even when you
need both hands for other tasks.
Now available with a MiniSPL microphone
holder, offering a space to store your mic.

Minstruments System Case

Store your valuable Minstruments test
system consisting of the Minirator MR1, the
Minilyzer ML1 or Acoustilyzer AL1 and the
MiniSPL adequately in the compact system
case which gives you extra space for cables,
connectors and other accessories you may
wish to bring along when you are ‘out in the
elds’ checking audio systems.

85

8. Technical Specication

Measurements

• Sound Pressure Level

• Real Time Analyzer

• Zoom FFT

• Reverberation Time

• Delay Time

• Level RMS

• Distortion THD+N

• Frequency

• Polarity Test

• Speech Intelligibility STI-PA (optional)

Sound Pressure Level

• SPL, Leq, Lc peak, Lmin, Lmax acc. IEC 61672

• Timer for single and repeated measurements

• Dynamic range (using MiniSPL): 30 - 130 dBSPL

A

• Filters: Flat, A, C, X-Curve-1, RLB (Broadcast Loudness)

• Logging of SPL/RTA results into AL1 memory

• Wideband- and RTA values simultaneously available

Real Time Analyzer

• 1/3 or full octave band resolution, class 0 lters

• SPL, LEQ and Max-Min display per band

Zoom FFT

• Real-time Zoom FFT with 50% overlapping, 93 Bins

• Frequency Range: 10 Hz - 20 kHz

• Resolution: 187.5 Hz to 0.73 Hz

Reverberation Time

• Octave band resolution, 63 Hz - 8 kHz, based on T20 results,
according to ISO3382.

• Automatic averaging with individual result readout and storage

• Source signal: Gated pink noise (CD included)

Delay Time

• Propagation delay between electrical and acoustical signal
input using built-in mic. Resolution < 0.1ms, max time: 1 s

• Dedicated test signal: NTI chirp (CD included)

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87

Electrical

• Level RMS, THD+N, Frequency, Polarity

STI-PA (Option)

• Single value STI and CIS test result. Modulation indices
and individual band level results accessible. Error indicator.

• Fullls the IEC 60268-16 release 2003 standard

(including amplitude weighting)

• TNO veried algorithm

PC Interface

• MiniLINK USB interface with PC software and
interface cable included

Frequency

• Range 10 Hz to 20 kHz

• Resolution 4 digits

• Accuracy < ± 0.1 %

Level

• Units dBu, dBV, V

RMS

• Resolution 3 digits (dB-scale) or 4 digits (V-scale)

• Accuracy ± 0.5 % @ 1 kHz

• Bandwidth 20 Hz to 20 kHz

• Flatness ± 0.1 dB

THD+N (Total Harmonic Distortion + Noise)

• Measurement Bandwidth
10 Hz to 20 kHz

• Resolution 3 digits (dB-scale) or 4 digits (%-scale)

• Residual THD+N
balanced < -85 dB @ -10 dBu to +20 dBu

unbalanced < -74 dB @ 0 dBu to +14 dBu

Polarity Test (with MR1 test signal)

Positive / Negative detection through internal microphone or XLR

RCA connector. Checks polarity of midrange-speakers, woofers,
sub-woofers and cables. Down to 10 dB S/N ratio of input signal.

Filters

• Flat • C-weighting • Highpass 400 Hz

• A-weighting • X-Curve

-1

• Highpass 19 kHz

87

Input Connectors

• XLR balanced, RCA unbalanced

Input Impedance

• 40 kOhm balanced, 20 kOhm unbalanced

Input RMS ( upper measurement limit )

• balanced +20 dBu (7.75 V

RMS

)

• unbalanced +14 dBu (3.8 V

RMS

)

• for input levels > 20 dBu (balanced) the Adapter -20 dB is

available as accessory

Max. DC Input

• ± 50 V

DC

Residual Noise

• < 12 µV, XLR-input shorted

Internal Microphone (for Polarity and Delay measurement only)

• Omni directional

Monitor Output

• Jack 3.5 mm (1/8“), suitable for all common headsets

Display Graphic LCD 64 x 100 pixel, with backlight

Batteries

• 3x AA batteries (alkaline)

• Typical battery lifetime > 16 hrs

Dimensions (L x W x H)

• 163 x 86 x 42 mm (6.4“ x 3.38“ x 1.63“)

Weight

• 300 g (10.5 oz) incl. batteries

Temperature

• 0° to +45° C (32° to 113° F)

Humidity

< 90 % R.H., non condensing

88

89

9. Appendix: Introduction to STI-PA

Application:

In case of emergency, public address systems in buildings like airports,
railway stations, shopping centers or concert halls have to (clearly)
inform persons in danger about escape information and directions.
However if such announcements are misunderstood due to poor system
quality, tragic consequences may result. Therefore, it is essential
to design, install and verify sound reinforcement systems properly
for intelligibility. In addition, a variety of other applications such as
legal and medical applications may require intelligibility verication.

Standard:

The IEC 60849 standard (national standards - see table) requires the
verication of electro acoustic sound systems for emergency purposes to
ascertain a minimum level of speech intelligibility in case of an emergency
under realistic circumstances. Thereby, speech intelligibility from a
regulatory view is not a subjective measurement, but can be veried with
several, more or less complex methods that have been standardized in IEC
60268-16.

National standards:

• IEC 60849 Sound systems for emergency purposes (also VDE 0828

part 1 and DIN-EN, BS-EN, SN-EN, OEVE-EN, …)

• NFPA 72 National Fire Alarm Code 2002 (2002 edition, section 7.4.1.4)

• BS 5839-8 Fire detection and alarm systems for buildings. Code

of practice for the design, installation and servicing of voice alarm
systems

Subjective Testing Methods:

Although frequency response, distortion or loudness all are important
to intelligibility, conventional measurements of these same parameters
together only marginally relate to intelligibility. When added issues such as
directionality of drivers and the environment are taken into consideration,
the question then is how well a spoken message can be understood at
different locations.

One approach is to let a trained human speaker read a number of
existing or synthetic words, whereas a representative number of listeners

89

individually write down what they believe of having understood. The
statistical analysis of these notes results in a value representing the
percentage of the listeners who have understood the messages correctly.

Important procedures according to this method are PB-words, CVC or SRT
(Speech Reception Threshold). However, conducting such tests is rather
costly, and in some hazardous locations, even impossible. Therefore,
these methods are mainly used to verify technical principles during
development.

Technical Methods:

Already back in 1940, Bell Laboratories started to develop measurement
technologies to determine the speech intelligibility. Nowadays, highly
developed algorithms as SII (Speech Intelligibility Index) and various
forms of the STI (Speech Transmission Index) allow measuring speech
intelligibility. These techniques take care of many parameters which are
important for intelligibility such as:

• Speech level

• Background noise level

• Reections

• Reverberation

• Psycho acoustic effects (masking effects)

Measurement techniques use synthesized test signals that don’t sound like
speech, but which have many common characteristics to real speech signals.
The averaged frequency response, as well as low frequency modulation,
is based on human speech. Since the speech of men’s and women’s
voices sound different, some measurement techniques use separate male
and female test signals: Speech intelligibility measurements acquire and
evaluate the signals in a manner characteristic of the way human speech is
altered before reaching the ears of a listener. Extensive investigations have
shown the relationship between the alteration of speech characteristics and
the resulting speech intelligibility. These ndings are incorporated into the
speech intelligibility meter that is able to display the intelligibility result as
a single number between 0 (unintelligible) and 1 (excellent intelligibility).

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91

STI, RASTI or STI-PA

STI, RASTI or STI-PA are the most established methods for measuring
speech intelligibility. All three of them basically apply the same principle,
whereby RASTI and STI-PA are a simplied version of STI. This article
explains the principles behind these methods.

Speech Model:

First of all, measuring the speech intelligibility requires a model for speech
signals. For instance, speech may be described as superposition of various
phoneme frequencies that are modulated (i.e. of which the amplitude is
varied).

Frequency Spectrum:
The frequency analysis of a male voice
over a certain period results in a typical
characteristic as shown in Figure 1.

Fig. 1: Averaged octave
band spectrum of a male
speaker.

Time Modulations:
Within each frequency band, the signal
level varies, i.e. it is “modulated” by the
speaker. Figure 2 shows the envelope of a
speech signal in the 250 Hz band, whereby
the shape of the envelope is given by the
speech contents.
By analyzing the spectra of envelope
sequences it can be shown that a speaker
modulates the individual frequency bands in
the range from 0.2 to 12.5 Hz.

Fig. 2: Envelope of a speech
signal (250 Hz band).

Fig. 3: frequency spectrum
of the envelope of a speech
signal (250 Hz band).

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Modulation Transfer Function (MTF)

For a high speech intelligibility it is mandatory that the integrity of the
modulations of the transmitted voice signal be preserved. Therefore, the
three core intelligibility measurement methods, STI, RASTI und STI-PA are
based on measuring the MTF (Modulation Transfer Function). This function
quanties the degree to which the voice modulations are preserved in the
individual frequency bands.

The envelope shown in Figure 3 is divided into 1/3rd octave band
frequencies, thus resulting in 14 frequency bands between 0.63 and 12.5
Hz. The modulation transfer function determines for each of the 7 voice
bands (refer to Figure 1) how well the modulations are preserved.

Based on the MTF results as well as further parameters such as the
sound pressure level, hearing threshold, frequency response or psycho
acoustic effects (masking effects) it becomes possible to reliably determine
the speech intelligibility. The corresponding calculations are based on
extensive and profound evaluations and comparisons with subjective
methods that are optimized continuously. Measuring the complete
MTF – as required for STI – can become rather complex. For instance,
14 * 7 = 98 individual measurements must be executed, thus resulting in
a total acquisition duration of 15 minutes. Therefore, different approaches
have been developed to reduce the test period and to enable speech
intelligibility measurements with portable instruments.

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93

STI - Speech Transmission Index

The STI result is based on the complete set of 98 measurements. Since
this approach requires a rather long test period, it is less frequently applied
in practice. However, STI represents the most detailed method to measure
the speech intelligibility and is mostly used if alternative approaches do not
provide reliable results due to unfavorable environmental conditions.
In practice, the STI result is preferably calculated out of the impulse
response (MLSA) that has been acquired e.g. with a PC-based system.
This approach is much quicker, but requires a lot of experience and
especially a linear behavior of the setup, i.e. there must be no non-linear
processing or conditions, including compressors or limiters, which is a
rather rare situation.

RASTI - Room Acoustics Speech Transmission Index

RASTI acquires only few segments of a complete MTF, which at rst glance
obviously represents an extreme simplication of STI. Therefore, tight use
restrictions must be met to acquire reliable speech intelligibility results with
RASTI. Furthermore, the RASTI result does not consider signicant and
practical auxiliary parameters such as the frequency response, echoes or
frequency-dependant reverberation times.

For a RASTI measurement, only two simultaneously generated frequency
bands are considered, i.e. the 500 Hz and the 2 kHz band which then are
modulated with four and ve frequencies respectively.
The practical application of RASTI is mainly restricted to acquisitions
between two persons. However, RASTI used to be the only method to
measure the speech intelligibility with a portable instrument for a long time

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STI-PA - Speech Transmission Index for Public Address Systems

A rising awareness for security issues, new technological means and the
shortcomings of RASTI triggered the speaker manufacturer Bose and the
research institute TNO to develop a new method for speech intelligibility
measurements of PA installations. The result of these efforts is STI-PA,
which allows quick and accurate tests with portable instruments.

Like RASTI, STI-PA applies a simplied procedure to calculate the MTF.
But STI-PA determines the MTF by analyzing all seven frequency bands,
whereby each band is modulated with two frequencies.
Supposing that no severe impulsive background noise is present and
that no massive non-linear distortions occur, STI-PA provides results as
accurate as STI. If however impulsive background noise is present during
the normal system operation hours, it is usually possible to mitigate the
effects by also acquiring a measurement at a more favorable time e.g.
under slightly different conditions in the area, or during the night time - and
to calculate an unbiased overall measurement by using the results of both
test cycles.

NTI STI-PA measurement table:

Portable STI-PA analyzers, e.g. NTI’s Acoustilyzer, are able to evaluate
speech intelligibility within 15 seconds per position and are thus well suited
for wide-area measurements and high productivity.

Read more on the web site “http://www.nt-instruments.com/acoustilyzer.”.

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