NEUTRIK RT-1M User manual

V 3.32 / Feb. 99
\\NTI_SVR1\Instdata\RAPID-TEST\RT-1M\U_Manual\text\RT1M332.doc
8VHU0DQXDO
>@9
Multitone Audio Test System
Version 3.32 E
For Firmware Revision
3.25 and higher

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INTERNATIONAL WARRANTY
Limited Warranty
NEUTRIK guarantees the >@9 system and its components against defects in material or
workmanship for a period of one year from the date of original purchase for use and agrees
to repair or replace any defective unit at no cost for either parts or labor.
Important
This warranty does not cover damage resulting from accident, misuse or abuse, lack of
reasonable care, the affixing of any attachment not provided with the product, loss of parts
or connecting the product to any but the specified receptacles. This warranty is void unless
service or repairs are performed by an authorized service center.
No responsibility is taken for any special, incidental, or consequential damages. In case of
damage please take or ship prepaid your >@9 System to your nearest authorized service
center. Be sure to include your sales invoice as proof of purchase date. All transit damages
that may eventually occur are not covered by this warranty.
Note
No other warranty, written or oral, is authorized by NEUTRIK. Except as otherwise stated in
this warranty NEUTRIK makes no representation or warranty of any kind, expressed or
implied in law or in fact, including, without limitation, implied merchantability or fitness for any
particular purpose and assumes no liability, either in tort, strict liability, contract or warranty
for products.
NEUTRIK AG
Im Alten Riet 34
FL-9494 SCHAAN
Liechtenstein
Tel: +41 (0)75 / 237 24 24
Fax: +41 (0)75 / 232 53 93
WARNING! Read this manual and especially chapter
2I NSTALLATION carefully before
operating the instrument. Important information about mains voltage
selection and fuse rating are given there.
Do never open, modify or try to repair this instrument unless properly
instructed by an authorized service technician or NEUTRIK.

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CE DECLARATION OF CONFORMITY
We, the manufacturer
NEUTRIK CORTEX Instruments AG
Im Alten Riet 34
FL-9494 Schaan
hereby declare that the product
Product Name Rapid-Test
Model Number RT-1M
Serial No .
Year of Construction 1996
conforms to the following standards or other normative documents
EC-Rules 89/392, 91/368, 93/44, 93/68, 73/23, 89/336, 92/31
Harmonized Standards IEC 65, IEC 68-2-31, IEC 348
EN50081-1, EN50082-1, EN50140, EN 61010-1
This declaration becomes void in case of any changes on the product without written
authorization by NEUTRIK.
Date Schaan, 12. August 1996
Signature
Position of Signatory Product Manager Test Instruments
Samples of this instrument have been tested and found to conform
with the statutory protective requirements. Instruments of this type
thus meet all requirements to be given the CE mark.

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TABLE OF CONTENTS
1 OVERVIEW .......................................................................................9
Communication.................................................................................................9
Accessories & Options .....................................................................................10
Software Tools.......................................................................................................10
Application Notes...................................................................................................10
DTMF Option.........................................................................................................10
Microphones & Phantom Power Supply.................................................................10
2 INSTALLATION...................................................................................11
Unpacking.........................................................................................................11
Rack Mount ......................................................................................................11
AC Power Connection......................................................................................11
Mains Cable......................................................................................................12
IEEE Connection..............................................................................................12
IEEE Address Selection.........................................................................................12
Audio Connection.............................................................................................12
Balanced Connection.............................................................................................13
Unbalanced Connection.........................................................................................13
Battery Low Indication............................................................................................13
LED Indicators..................................................................................................14
Power ....................................................................................................................14
Interface ................................................................................................................14
Calculating.............................................................................................................14
Trigger...................................................................................................................14
Overload................................................................................................................14
Error ......................................................................................................................14
Test of Function................................................................................................15
HT-BASIC Program Example.................................................................................15
3 SYSTEM DESCRIPTION ......................................................................16
Multitone Signals..............................................................................................16
Multitone Parameter...............................................................................................17
Sampling Rate...................................................................................................17
Blocklength .......................................................................................................18
Frequency Spacing ...........................................................................................18
Bins...................................................................................................................19
Phase / Crest Factor Optimization.........................................................................19
Comparability of Multitone Measurements.............................................................20
Signal Table...........................................................................................................20
Blocklength 512.................................................................................................20
Blocklength 1024...............................................................................................21
Blocklength 2048...............................................................................................21
Blocklength 4096...............................................................................................21
Blocklength 8192...............................................................................................21
Generator .........................................................................................................22
Block Diagram .......................................................................................................22
Digital Section........................................................................................................22
Analog Section.......................................................................................................22
Analyzer............................................................................................................23
Block Diagram .......................................................................................................23

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Analog Section.......................................................................................................23
Filtering.............................................................................................................23
Digital Section........................................................................................................24
Definition of Multitone Signals..........................................................................24
Header...................................................................................................................25
Multitone Signal.....................................................................................................26
Data Acquisition................................................................................................26
Wake-up Sequence...............................................................................................26
Synchronization Mode............................................................................................26
INTernal............................................................................................................26
INTNoheader.....................................................................................................27
EXTernal...........................................................................................................27
EXTNoheader ...................................................................................................27
Gathering Data......................................................................................................27
Signal Analysis & Result Queries.....................................................................28
Level......................................................................................................................28
Distortion ...............................................................................................................28
RMS and RSS Value.........................................................................................29
Interpretation of TD+N.......................................................................................29
Distortion Plot....................................................................................................29
Full Band TD+N Measurement..........................................................................30
THD+N Calculation ...........................................................................................30
MT-SINAD.........................................................................................................30
RSS Selective Measurement.............................................................................31
Noise .....................................................................................................................32
Full Band Noise.................................................................................................32
Crosstalk................................................................................................................33
Phase ....................................................................................................................34
DTMF Mode......................................................................................................34
Broadcast Mode ...............................................................................................35
Mode of Operation.................................................................................................35
Setup.................................................................................................................35
Trigger Configuration ........................................................................................36
Application Hints / Troubleshooting...................................................................37
4 PROGRAMMING.................................................................................39
Command Structure .........................................................................................39
IEEE-488.1 Compatibility.......................................................................................39
IEEE-488.2 Commands.........................................................................................39
Command Summary..............................................................................................39
Descriptive Symbols ..............................................................................................40
Command Notation................................................................................................41
Command Set...................................................................................................42
SYSTem Subsystem..............................................................................................42
SYSTem:RESet ................................................................................................42
SYSTem:ERRors? ............................................................................................42
SYSTem:INFormation?.....................................................................................43
INPut Subsystem...................................................................................................44
INPut:FRONt [ON¦OFF].....................................................................................44
INPut[1-2]:LINK [OFF¦ON].................................................................................44
INPut[1-2]:RANGe <Range> <Unit>..................................................................44
INPut:SYNC [INTernal¦INTNoheader¦EXTernal¦EXTNoheader] ........................45
INPut:SWFilter [OFF¦CWE¦CCITT]....................................................................45
INPut:DEEMphasis [OFF¦ON] ...........................................................................46

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INPut:TRIGger:ARMed......................................................................................46
INPut:TRIGger:ARMed?....................................................................................46
INPut:TRIGger:BREak ......................................................................................47
INPut:TRIGger:CONFiguration [LOOSE¦TIGHT¦USER]....................................47
INPut:TRIGger:USRConfiguration
<setbin1(dB)>,<setbin2(dB)>,<emptybin(dB)>..........................................47
INPut:TRIGger:USRConfiguration?...................................................................48
INPut[1-2]:STATus?..........................................................................................48
OUTPut Subsystem...............................................................................................49
OUTPut:MTONe:PARameter <Parameter>.......................................................49
OUTPut[1-2]:LEVel <Level> <Unit> ..................................................................49
OUTPut:MTONe:PRETriggerlength <Length> ..................................................50
OUTPut:MTONe:MTONelength <Length>.........................................................50
OUTPut[1-2]:BINlevel <Level> <Unit>...............................................................51
OUTPut[1-2]:MUTe [OFF¦ON]...........................................................................51
OUTPut:FLOAT [OFF¦ON]................................................................................51
OUTPut:MTONe:ACTive [1¦2¦3¦4]......................................................................52
OUTPut:MTONe:STARt....................................................................................52
OUTPut:MTONe:CONtinuous ...........................................................................52
OUTPut[1-2]:STATus?......................................................................................52
OUTPut:MTONe:NAME?...................................................................................53
OUTPut:MTONe:BLOCklength?........................................................................53
OUTPut:MTONe:PARameter? ..........................................................................53
OUTPut[1-2]:MTONe:CRESt?...........................................................................54
MEASurement Subsystem.....................................................................................55
MEASurement[1-2]:LEVel:UNIT [dBVp¦Vp¦dBV¦V] ............................................55
MEASurement[1-2]:LEVel? ...............................................................................55
MEASurement[1-2]:DISTortion:UNIT [dBV¦V]....................................................55
MEASurement[1-2]:DISTortion?........................................................................55
MEASurement[1¦2]:MTSinad?...........................................................................56
MEASurement[1-2]:SELectiverss:UNIT [dBV¦V]................................................56
MEASurement[1-2]:SELectiverss? <binstart> <binstop>...................................57
MEASurement[1-2]:NOISe:UNIT [dBV¦V]..........................................................57
MEASurement[1-2]:NOISe?..............................................................................57
MEASurement[1-2]:CROSstalk:UNIT [dB¦%].....................................................58
MEASurement[1-2]:CROSstalk?.......................................................................58
MEASurement:PHASe:UNIT [rad¦deg]..............................................................58
MEASurement:PHASe:SCALe <Scale>............................................................58
MEASurement[1-2]:PHASe?.............................................................................59
MEASurement1:DTMF:STARt...........................................................................59
MEASurement1:DTMF?....................................................................................59
Device Status.........................................................................................................60
*STB?................................................................................................................60
*OPC.................................................................................................................60
*OPC?...............................................................................................................60
*CLS..................................................................................................................61
*ESE .................................................................................................................61
*ESE? ...............................................................................................................61
*SRE.................................................................................................................61
*SRE?...............................................................................................................62
*ESR?...............................................................................................................62
*PSC.................................................................................................................62
*PSC?...............................................................................................................63
*IDN? ................................................................................................................63
*RST .................................................................................................................63

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*TST?................................................................................................................63
*WAI..................................................................................................................64
Examples ..........................................................................................................64
Use of an *OPC command ...........................................................................64
Use of MAV bit in the status Byte register.....................................................64
IEEE Standard Status Data Structure....................................................................65
5 APPLICATION HINTS..........................................................................66
Arbitrary Generator...........................................................................................66
Alignment and Adjustments for Audio Repair Facilities....................................66
Cellular Phone Testing.....................................................................................66
Rub & Buzz Speaker Testing............................................................................66
RT-EVAL Software Package............................................................................67
Units & Conversion...........................................................................................67
6 SPECIFICATIONS...............................................................................69
Generator .........................................................................................................69
Analyzer............................................................................................................69
General.............................................................................................................69
7 INDEX..............................................................................................70

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1 OVERVIEW
The trend in modern audio testing is to reduce more and more the time required for a
complete performance test of the device being tested. This tendency results partly from the
demand of broadcasters being forced to provide 24hour programming, leaving little time for
testing. In a modern studio with dozens of input channels, several routing paths and more
than 24 recording channels, a complete test including all parts of the studio becomes very
time-consuming and boring since the tests are highly repetitive.
Industrial applications also require reduced test time, especially at production lines where
any time wasting process becomes a bottleneck. Reducing test time by a factor of 20 to 50
ensures for years that testing will not be the limiting factor and increases production density.
>@9 is a modern and advanced audio test system with the capability to evaluate the
important performance Parameter of a device within a fraction of a second. >@9 is a
complete, optimized system, containing a remote controllable generator as well as an
intelligent analyzer, and can be easily integrated into an automated environment. The
system provides the highest performance and specifications to meet also the requirement of
professional equipment.
•
Frequency range 20Hz to 20kHz
•
Output level -60dBVp to +20dBVp
•
Input range -60dBVp to +20dBVp
•
Measurements level, noise, distortion, crosstalk and phase in one step
•
Burst transmission time typ. 250-960ms
•
Residual distortion < -86dB
>@9 is very simple in terms of connecting, handling and use within any automated
environment, but highly complex in terms of the implemented structures and algorithms to
perform the analysis in a extremely short period of time.
>@9 is very compact, using the most advanced technology available on the market. Within
its case of 19“ width and height of one unit (1.75“) only, it provides two generator channels
and two independent analyzer channels. The analyzer and generator can be operated
completely independently even though they are located in the same housing.
There is no external synchronization required to perform the analysis. Each transmitted
multitone signal contains an information header allowing any listening analyzer to
synchronize onto the signal.
Communication
Since >@9 does not provide any control elements, it must be completely controlled by a host
PC. Due to performance reasons, an IEEE-488 parallel interface has been integrated into
the instrument. This allows to transmit any command independently of the actual generator
and/or analyzer activities. The instruction to transmit a previously defined multitone signal
can be issued from the PC at any time.
Consequently, the basic requirements for the host PC is a standard IEEE-488 interface
board with installed software drivers. Detailed descriptions of the IEEE-488 connection and
all commands are filed in chapters Mains Cable and Programming respectively.

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Accessories & Options
Software Tools
Following software packages for >@9 are available free of charge from your local NEUTRIK
representative.
• RT-EVAL Evaluation Software
• LabView® Driver Library
• LabWindows® CVI Driver Library
Please notice, that for either of these tools a GPIB-interface board from National
Instruments(type GPIB-PCMCIA or GPIB/TNT or GPIB-PCIIA [production year 1992 or
later]) must be installed in your host controller.
Application Notes
The appendix of this User Manual comprises the documents
• Introduction to >@9
• Get Familiar with Writing Code for >@9
• Cellular Phone Testing
• Comparison of Conventional vs. Multitone Testing
Additional application notes on speaker testing, external signal analysis etc. will be released
in future. Please contact you local NEUTRIK representative for further information.
DTMF Option
Optional PCB to be installed internally, allowing to monitor 1 channel on incoming DTMF
(Double Tone Multiple Frequency) signals in parallel to the normal operation (see p. 34).
Microphones & Phantom Power Supply
NEUTRIK provides two measuring microphones for industrial applications.
• 3382 ¼" measuring microphone
• 3384 ½" measuring microphone
To allow the use of these microphones with >@9, an optional Phantom power box is
available to provide the necessary supply voltage through XLR connectors. The box is
plugged to the input banana connectors and comes along with an AC mains adapter.

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2 INSTALLATION
This chapter is intended as help for proper unpacking and installation of the >@9 system.
Please read it carefully to avoid wrong connections or inconveniences during operation of
the instrument.
Unpacking
>@9 has been carefully packed by NEUTRIK to avoid damages during transportation.
Should the box show severe damages, please immediately check the instrument inside on
external impacts. In case of any visible damage, please do not send the instrument back but
contact your local dealer and / or the carrier to avoid loss of claims for replacement.
Rack Mount
>@9 is designed to mount in a 19“ Rack and occupies one unit of height or rack space
(1.75“) only. Please allow at least 2“ additional depth at the rear side for all necessary
connectors. Make sure there is enough air circulation around the unit for cooling purposes
and please do not place >@9 besides high temperature devices such as power amplifiers in
order to avoid overheating.
The specified operating temperature ranges between 5° and 45°C (40-110F) while humidity
must not exceed 90% R.H. non-condensing.
AC Power Connection
Before connecting the instrument via mains cable to the power source, make sure that the
voltage selector label on the connector / fuse holder assembly of the >@9 system matches
the supply voltage of the local area. If the instrument is not compatible with the available
power source, follow the next paragraph to change the voltage selector.
>@9 can operate from 100VAC, 120VAC and
230VAC sources. To reconfigure the input line
voltage, remove the power cable and open the
flap of the connector/fuse holder at the rear
side of >@9. Either press a small screwdriver
into the slot to open the flap as shown in Fig. 1
or ruin your fingernails.
Take out the drum and insert it in the new position so that the matching voltage indication
points towards you. At the same time replace the mains fuse with the proper current rating.
For voltages of 100V to 120V a slow 2A fuse has to be installed, while for 230V a slow 1A
fuse is appropriate.
After selection of the correct mains voltage and fuse, close the flap and insert the power
cable.
>@9 is designed with a protective ground (earth) connection through
the ground wire of the power cord. This connection is essential for
safe operation. Never operate the instrument if safety ground is
unavailable or has been compromised.
Fig. 1 Voltage Selector

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Mains Cable
The enclosed mains power cable has an unconnected end with three colored leads, which
correspond to
Brown = Live (AC)
Blue = Ground
Yellow/Green = Earth
Attach a mains plug to the cable that fits the receptacles of your country.
IEEE Connection
The >@9 system provides an IEEE-488 interface (standard design interface for
programmable instrumentation) which is connected to the IEEE bus using a standard IEEE-
488 interface cable from the rear panel illustrated in Fig. 2.
With the IEEE interface bus, up to 31 instruments can
be interconnected. The cables have identical piggy-
back connectors on each end so that several cables
can be connected in virtually any configuration. There
must be, of course, a path from the computer to every
device operating on the bus.
As a practical matter, avoid stacking of more than
three or four cables to a single connector. If the stack
gets too long, any force on the stack can damage the
connector mounting. Be sure that each connector is
firmly screwed in place.
IEEE Address Selection
Each IEEE device has at least one talk and listen address (unless totally transparent or a
talk or listen only device). The address of the >@9 can be adjusted with the DIP switch at
the rear panel of the instrument (see Fig. 2). Each switch position has a number printed
underneath. The resulting IEEE address is the sum of all numbers, where the switch is in
position “1“. The above illustrated example has an address selection of 3, since switch 1 and
switch 2 are in position "1". The five switches allow the selection of any address in the range
from "1" to "31" inclusively.
Audio Connection
>@9 features balanced and unbalanced BNC and 4mm banana connectors for both inputs
and outputs. Balanced connections enhance the noise and hum immunity and are always
recommended for measurement purposes. >@9 can also handle unbalanced signals.
Unbalanced signals normally have one hot signal
against chassis ground. For this reason unbalanced
connections are recommended for short connections
only (less than 1m / 3 feet) or in a relatively noise-free
environment.
You may use either the set of front connectors with two
inputs & outputs or the equivalent set of connectors at
the rear panel of the instrument.
Caution: Do not connect both front and rear panel connectors at the same time
since this may result in signal mismatching.
Fig. 2 IEEE Connector
Fig. 3 Front Connectors

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Connections between an unbalanced DUT
and the balanced inputs of >@9 should
preferably be made with shielded twisted
pair cables to avoid the introduction of
noise and hum. The shield of such a cable
shall be grounded only on one side.
Grounding the shield on both sides
increases the chance to build ground loops.
Balanced Connection
Balanced connections with two BNC cables can be realized by connecting them to the >@9
HIGH and LOW inputs. The ground shells of both connectors are wired to ground. Do not
connect the shields together on the instrument side of the DUT but leave them open. With
balanced connections do not assemble the short circuit bar.
You may also use banana inputs instead of BNC inputs. The respective HIGH and LOW
inputs of the BNC and banana connectors are internally wired together.
Caution: For balanced signals make sure that not only the front ground connection
is disassembled but also the ground bar at the rear panel!
Unbalanced Connection If you use the HIGH input only of >@9
for connecting the hot output of the DUT,
use the BNC cable’s shield as the return
signal (common of the DUT output).
When using the generator in unbalanced
mode, the available level will always be
6dB (50%) below the defined level.
Battery Low Indication
>@9 contains a battery for backup purposes of the internal memories. Life expectancy of
the battery is about ten years. Should the battery become low, the 'Error' LED will blink 3 to 4
four times after a start-up and Error 220 Battery low (memory backup) is generated.
Fig. 4 Shielded Twisted Pair Cable
Fig. 5 Balanced BNC / Banana Connection
Fig. 6 BNC Cable - Balanced
Fig. 7 Unbalanced Connection

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LED Indicators
During the initialization period of >@9 system (normally <1s) all LEDs are active. If the
unit is switched ON for the very first time or after a firmware change, it has to initialize
all its signals and tables. This might take up to a few minutes, depending on the
signal resolution. All LEDs are lit during this period.
Power This LED indicates that the power of the system is switched on,
the internal supply voltages are operating normally and the self-
test of the system has been successfully completed.
Should it stay off after switching on the instrument please check
whether the power cable is connected to the system, the voltage
selector is set for the correct supply voltage and the wall socket is
switched on.
Should the power LED still be off, check the power fuse in the
connector / fuse holder assembly of >@9. Please refer to AC
Power Connection to see how to open it.
WARNING Do not try to do further repairs. Call your local dealer for support.
Interface
This LED indicator lights up if the IEEE interface is busy and receives a command. It
remains illuminated until the user has read the answer from the interface. In standby mode
with no activity on the IEEE interface the LED is off.
Calculating
Whenever FFT or filtering calculations are performed this LED lights up.
Trigger
This LED indicator goes on as soon as a >@9 trigger has been successfully detected and
remains lit until the user has read the result(s) from the buffer.
Overload
Should the input signal overload one or both channels, the LED indicator goes on. This
happens if the maximum input voltage of 20dBu (10V) is exceeded or if a higher voltage than
the selected range is applied. In such a case the error LED also lights up. The overload LED
resets with the next measurement and the ranges set correctly.
Error
>@9 handles an error queue internally. Whenever an error is detected – hardware or
software – the error LED comes on. It disappears as soon as the error number has been
queried through the IEEE interface.
Fig. 8 LED Indicators

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Test of Function
After connection of the cables and proper setting of the IEEE address it is recommended to
run the subsequent short program to confirm the proper function of the system. >@9 can be
operated with any operating system providing an IEEE-488 interface.
HT-BASIC Program Example
10 ! RT-1M Demo Program
20
30 Adr=11 ! enter IEEE address here
40
50 Adr=Adr+700 ! evaluate output/enter address J
51 GOSUB 900 ! read device informations
60 OUTPUT Adr;"Output:Mtone:Active 1" END
65 OUTPUT Adr;"Output:MTone:Start" END ! measurement loop
70 OUTPUT Adr;"Measurement1:Level?" END ! terminate output with END
80 GOSUB 1000 ! read the measurements
90 PRINT
100 GOTO 65
110 STOP
900 ! read system information
905 DIM Inf$[100]
910 OUTPUT Adr;"System:Information?" END
920 ENTER Adr;Inf$
930 PRINT Inf$
940 RETURN
1000 ! interpret incoming data stream
1010 DIM Rcv$[1000]
1020 DIM X$[10]
1030 DIM Y$[20]
1040
1050 ENTER Adr;Rcv$ ! read data A
1060 Xpos=POS(Rcv$,"/") ! find X/Y separator
1070 Ypos=POS(Rcv$,",") ! find Y/X separator
1080
1090 WHILE (Xpos>0) AND (Ypos>0) ! as long as there are separators do:
1100 X$=Rcv$[1,Xpos-1] ! isolate X value
1110 X=VAL(X$) ! convert X string to value A
1120 Ypos=POS(Rcv$,",") ! find Y/X separator
1130 IF Ypos>0 THEN ! is there another value? >
1140 Y$=Rcv$[Xpos+1,Ypos-1] ! isolate Y value
1150 ELSE
1160 Y$=Rcv$[Xpos+1,LEN(Rcv$)] ! isolate Y value
1170 END IF
1180 Y=VAL(Y$) ! convert Y string to value
1190 Rcv$=Rcv$[Ypos+1,LEN(Rcv$)] ! delete the read XY pair from string
1200 Xpos=POS(Rcv$,"/") ! find next X/Y separator
1210 PRINT "Bin# ",X,"Meas: ",Y
1220 END WHILE
1230 RETURN
1240 END

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3 SYSTEM DESCRIPTION
Multitone Signals
Traditionally, audio testing stimulates the device under test (DUT) with a sinusoidal signal.
This type of signal is relatively easy to handle and distortion measurements may be
performed by simply notching out the single frequency.
Fig. 9 Time Plot of Sinusoidal Signal Fig. 10 Spectrum of Sinusoidal Signal
More advanced tests like intermodulation distortion measurements stimulate the device with
a pair of sinusoidal signals to come closer to the real situation of audio signal transmission.
In the presence of nonlinear transfer characteristics, the DUT generates new harmonic and
intermodulation frequencies.
However, in practice the device is normally stimulated by music or speech which is a far
more complex signal than any single or twin tone test. Many frequencies with non-correlated
phase relations exist in such a real-world signal.
Therefore, multitone testing is a much more realistic approach for audio testing, emulating
the complex structure of natural sound. A multitone signal typically contains 2 to ~31 signal
frequencies, each with a certain phase relation, distributed over the frequency band of
interest. Obviously, sophisticated test instruments are necessary to analyze all these signals
with their interactions on each other.
Fig. 9 and Fig. 10 show a typical multitone signal in the time- and frequency domain. It is
important to know that the waveform of the time plot strongly correlates with the phase
relations between its single frequencies. Since the max. amplitude of the time signal directly
determines the dynamic range of both the DUT and the analyzer, a low peak value is both
important and desirable.
010 20 30 40 50 60 70 80 90
-1
-0.8
-0.6
-0.4
-0.2
0
0.2
0.4
0.6
0.8
1
Tme [ms]
Amplitude
2
0.5 1 1.5 Frequency [kHz]
Amplitude [dB]
-100
-90
-80
-70
-60
-50
-40
-30
-20
-10
0
1.5

>@9 Multitone Audio Test System  User Manual 
V 3.32 17 / 71
Obviously, it is necessary to characterize the time signal by an appropriate value in order to
allow the optimization of its phase relations. The most suitable value for this purpose is the
Crest factor , which is defined as
Crest factor Peak Value
RMS Value
=_
_
Equation 1 Crest Factor
For any (multitone) signal with given RMS value, the Crest factor will change with the peak
value, which in turn depends on the phases of the signal components. An optimal distribution
of the phases results in a low peak value of the resulting time signal and therefore a low
Crest factor (refer also to chapter Phase / Crest Factor Optimization).
NEUTRIK provides in its RT-EVAL software package a sophisticated algorithm to optimize
the phases of a multitone signal. Please contact your local representative to get a free copy
of this software
.
Multitone Parameter
>@9 is a digital processing system that analyzes the transmitted signal by using Fast
Fourier Transformation (FFT) and calculates with its DSP all desired results out of the
digitized samples.
For proper use and programming of >@9 it is vital to understand the core parameter of this
analysis as well as their relationships. Consequently, the most important definitions and
formulas are explained below.
Sampling Rate
Every digitization process, i.e. conversion of an analog signal into a digital bit stream and
vice versa, has to be accomplished at a certain
sampling rate (number of samples per
second). The sampling rate determines the analog bandwidth of the converter.
In >@9, the sampling rate is 48kHz, thus providing an analog bandwidth of up to 20kHz.
00.002 0.004 0.006 0.008 0.01
-1
-0.8
-0.6
-0.4
-0.2
0
0.2
0.4
0.6
0.8
1
Amplitude
Time
[
ms
]
0 4 8 12 16 20
Fre
q
uenc
y
[
kHz
]
-400
-350
-300
-250
-200
-150
-100
-50
0
Amplitude
[
dB
]
Fig. 11 Time Plot of a Multitone Signal Fig. 12 Spectrum of a Multitone Signal

>@9 Multitone Audio Test System  User Manual 
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Blocklength
The number of samples, that are actually used for one FFT, is called blocklength . This value
determines both the duration & the frequency resolution of a multitone signal. In >@9, the
blocklength may be selected by the user in five steps from 512 to 8192.
[]
MT Block Duration
Blocklengt
h
Sampling Frequency s=_
Equation 2 Duration of One Multitone Signal Block
Note A
>@9 multitone burst always comprises several multitone signal blocks,
thus resulting in a far longer duration than the ’MT Block Duration’ .
The blocklength also defines the lowest detectable frequency of the incoming spectrum. For
example, with a blocklength of 512 @ 48kHz sampling rate, a multitone block duration of
10.7ms results, corresponding to a min. frequency of ∆f = 93.75Hz (see Equation 3).
Furthermore, it is important to know that only signals with an integral number of periods
(reciprocal value of the signal frequency) fitting into one blocklength may be properly
analyzed by the FFT.
0 100 200
300
400 500
Sample Number
Fig. 13 The 5 Lowest Possible Time Periods @ Blocklength 512
In other words, only frequencies with an integral multiple of the lowest detectable frequency -
called frequency spacing ∆f - may be transmitted.
Frequency Spacing
The frequency spacing ∆f corresponds to the lowest frequency that can be generated &
analyzed. It defines the spectral resolution of the FFT and is calculated by following formula.
∆fSampling frequency
Blocklength Hz Blocklength
==
_’48000
Equation 3 Frequency Spacing

>@9 Multitone Audio Test System  User Manual 
V 3.32 19 / 71
Only frequencies with an integral multiple of ∆f may be defined as signal bins (see below) of
a multitone burst.
Example
Blocklength = 512 @ 48kHz sampling rate
⇒∆f = 93.75Hz
⇒available frequencies =
n * 93.75Hz ( n = integral number)
Bins
The frequencies, that may be transmitted in a multitone burst, are called bins . For a better
understanding, three types of bins have been introduced.
•
Signal bins are those bins (frequencies) that actually build the multitone signal.
•
Even bins are all the bins (frequencies) that emerge from Equation 3, i.e. the frequencies
that may be used as signal bins in a multitone signal.
•
Odd bins are an effect the internal FFT computation of >@9. They represent all bins
halfway between the even bins, i.e. as if the frequency spacing would equal ∆f/2.
The subsequent relations indicate the min. and max. available frequencies (
bins ) in a
multitone signal at 8kHz / 48kHz sampling rate (
f
s
).
{}
f f Hz may be generated onlymin =≥∆20
Equation 4 Minimum Signal Bin Frequency
{}
ff
kHz
fkHz may be displayedmax *=≤∆ ∆
20 20
Equation 5 Maximum Signal Bin Frequency
Besides the above equations there are no other constraints for the definition of a multitone
signal. This means you can use any bin representing a frequency below or equal to 20kHz
as a signal bin. It is up to the operator what the intention of the signal bins is. Please refer
also to chapter Signal Table.
Phase / Crest Factor Optimization
In order to achieve a low Crest factor, RT-EVAL – an evaluation PC-program provided free
of charge by NEUTRIK - offers a special feature that allows to optimize the phases of any
multitone signal. The results can be loaded directly from or back into the >@9 Generator.
Low Crest factors are important for two reasons. First, the peak level of the multitone signal
raises the necessary input range for the analysis and thereby reduces sensitivity for the low-
level signal components. Second, the low energy content of a multitone signal with high
Crest factor may barely stimulate the DUT.
A non-optimized multitone signal may show Crest factors of up to 10 (20dB), while with a
proper minimization algorithm, Crest factors as low as ~2 (6dB) can be found. This
difference of 14dB can directly enhance or decrease the dynamic range of the analyzing
system.

>@9 Multitone Audio Test System  User Manual 
20 / 71 V 3.32
Comparability of Multitone Measurements
One has to be aware that the results of multitone testing cannot be compared directly with
conventionally acquired results. For instance, distortion products may appear over the entire
band due to the fact that each signal bin produces harmonics and intermodulates with other
signal bins. The strict separation between harmonic distortion and intermodulation cannot be
guaranteed, since at certain signal bins some intermodulation products and harmonic
frequencies may fall together, thus influencing the Distortion as well as the SINAD results..
However, a multitone signal comes much closer to a "real-world“ signal than any single tone
test signal. The results are in qualitative terms comparable with conventional measurement
results as long as the specific theory behind multitone testing is considered. With a single
tone stimulus, the achieved results are directly comparable to conventional analyzers.
Please refer to the corresponding application note, filed in the appendix of this manual.
Signal Table
>@9 supports five different blocklengths. According to Equation 3 to Equation 5, each
blocklength results in the parameter of Table 1. Please observe that the minimum signal bin
frequency is ≥20Hz and that the overall duration of a burst always is longer than of a block.
Blocklength Min. Burst Duration
(without Header) Typical Burst Duration Generator Resolution Analyzer Resolution
512 154 ms 260 ms 93.8 Hz 46.9 Hz
1024 284 ms 390 ms 46.9 Hz 23.4 Hz
2048 344 ms 450 ms 23.4 Hz 11.7 Hz
4096 684 ms 790 ms 11.7 Hz 5.9 Hz
8192 854 ms 960 ms 5.9 Hz 2.9 Hz
Table 1 Available Blocklengths
Blocklength 512
Frequency spacing ∆f 93.75 Hz
Analyzer resolution 46.875 Hz
Bin_Min (fmin) 1 (93.8 Hz)
Bin_Max (fmax) 213 (19.969 kHz)
Table 2 Signal Parameter with Blocklength 512 @ fs=48kHz
00.005 0.01 0.015 0.02 0.025
-1
-0.8
-0.6
-0.4
-0.2
0
0.2
0.4
0.6
0.8
1
Crestfactor=7.87
Fig. 14 Non-Optimized Multitone Signal
00.005 0.01 0.015 0.02 0.025
-1
-0.8
-0.6
-0.4
-0.2
0
0.2
0.4
0.6
0.8
1
Crestfactor=2.71
Fig. 15 Optimized Multitone Signal