NEUTRIK RT-1M User Manual
V 3.32 / Feb. 99
\\NTI_SVR1\Instdata\ RA P ID-TEST\RT-1M\U_Manual\text\RT1M332.doc
8VHU0DQXDO
>@9
Multitone Audio Test System
Version 3.32 E
For Firmware Revision
3.25 and higher
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Multitone Audio Test System
User Manual
2 / 71 V 3.32
>@9
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User Manual
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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 f rom 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 specif ied 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 pur chase 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 lim itat ion, im plied merc hantabilit y or f itness f or any
particular purpose and assumes no liabilit y, 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
2 I
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 m anufacturer
NEUTRIK CORTEX Inst r um ents 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 Instrument s
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 prog ramming, leaving little time f or
testing. In a modern st udio with dozens of input channels, several routing paths and more
than 24 recording channels, a complete test including all parts of t he studio becomes very
time-consuming and boring since the t est s ar e highly repetitive.
Industrial applications also require reduced test time, especially at production lines where
any time wasting process becomes a bottleneck. Reducing t est time by a factor of 20 to 50
ensures for years that testing will not be the lim it ing 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 specif ications to meet also the requirem ent 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 com plex in terms of the implement ed 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 com pletely controlled by a host
PC. Due to performance reasons, an IEEE-488 parallel interface has been integrated into
the instrument. This allows to t ransmit 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 descript ions of the IEEE-488 connection and
all commands are filed in chapters Mains Cable and Programm ing respectively.
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Accessories & Options
Software Tools
Following software packages for >@9 are available free of charge f rom your local NEUTRIK
representative.
• RT-EVAL Evaluation Software
• LabView® Driver Library
• LabW indows® CVI Dr iver Libr ary
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 sig nal analysis etc. will be released
in future. Please contact you local NEUTRIK representative for f urther 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 t he nor m a l oper ation (see p. 34).
Microphones & Phantom Pow e r 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 instrum ent back but
contact your local dealer and / or the carrier to avoid loss of claim s 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 circulat ion around the unit for cooling purposes
and please do not place
>@9 besides high temperat ure devices such as power amplifiers in
order to avoid overheating.
The specified operating tem perature ranges between 5° and 45°C (40-110F) while humidity
must not exceed 90% R.H. non-condensing.
AC Power Connection
Before connecting t he instrument via mains cable to the power source, mak e sure that the
voltage selector label on the connector / f use 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 t he 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 mat ching voltage indication
points towards you. At the same time replace the mains f use 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 w ith a protecti ve ground (earth) connection t hrough
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 instrumentat ion) which is connected to the IEEE bus using a standard IEEE488 interface cable from t he r ear panel illustrated in Fig. 2.
With t he IEEE int erface bus, up t o 31 instruments can
be interconnected. The cables have identical piggyback connectors on each end so that several cables
can be connected in virtually any configuration. T here
must be, of course, a path f rom 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 connect or. If the stack
gets too long, any for ce 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 tot ally 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 result ing IEEE address is the sum of all numbers, where the switch is in
position “1“. The above illustr ated example has an addr ess 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 input s
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 f eet) or in a relatively noise-free
environment.
You may use either the set of front connectors with two
inputs & outputs or the eq uivalent set of connectors at
the rear panel of the instrument .
Caution: Do not connect both front and rear panel connect ors 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 toget her 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 inter nally wired toget her .
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 t he hot out put of t he DUT,
use the BNC cable’s shield as the retur n
signal (common of the DUT output).
When using t he 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 t en 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 initial i z at i on period of >@9 system (normally <1s) all LEDs are active. If the
unit is swi t ched ON for the very first time or after a firmware change, it has t o i ni t i al i ze
all its signals and tables. This might take up to a few minutes, depending on the
signal resolution. All LEDs are lit during this peri od.
Power
This LED indicates that the power of the system is switched on,
the internal supply voltages are operating normally and the selftest 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 f or 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 t he answer from the interface. In st andby mode
with no activity on the IEEE interface the LED is of f.
Calculating
Whenever FFT or filtering calculations are performed this LED lights up.
Trigger
This LED indicator g oes on as soon as a >@9 trigger has been successf ully 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 voltag e of 20dBu (10V) is exceeded or if a higher voltage t han
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 cor r ectly.
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 inter face.
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 progr am to conf irm the pr oper f unction of t he 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 sing le frequency.
Fig. 9 Time Plot of Sinusoidal Signal Fig. 10 Spectrum of Sinusoidal Signal
More advanced tests like intermodulation distortion measurem ents stimulate the device with
a pair of sinusoidal signals to come closer to t he real situation of audio signal transmission.
In the presence of nonlinear transfer char acteristics, the DUT generat es 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, multit one testing is a much more realistic approach for audio testing, emulating
the complex structure of natural sound. A mult itone signal typically contains 2 to ~31 signal
frequencies, each with a certain phase relation, distributed over the frequency band of
interest. Obviously, sophisticated test inst ruments 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 t he max. amplitude of the t ime signal directly
determines the dynamic range of both t he DUT and the analyzer, a low peak value is both
important and desirable.
0 10 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]
Ampli tude
2
0.5 1
1.5
Frequency [kHz]
Amplitude [ dB ]
-100
-90
-80
-70
-60
-50
-40
-30
-20
-10
0
1.5
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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 g iven RMS value, the Crest factor will change with the peak
value, which in turn depends on t he phases of the signal components. An optimal dist r ibut ion
of the phases result s in a low peak value of the resulting time signal and theref ore 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 mult itone signal. Please contact your local r epresentative to get a f ree 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 param eter 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 deter m ines t he analog bandwidth of the converter.
In
>@9, the sampling rate is 48k Hz, thus providing an analog bandwidth of up to 20kHz.
0 0.002 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
uency [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
18 / 71 V 3.32
Blocklength
The number of samples, t hat are actually used f or one FFT, is called
blocklength
. This value
determines both the duration & the f requency resolution of a multitone signal. In
>@9, the
blocklength may be selected by the user in five steps f r om 512 t o 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 detect able 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 m in. 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 m ultiple of the lowest detectable frequency called frequency spacing ∆f - m ay be tr ansm it t ed.
Frequency Spacing
The frequency spacing ∆f corresponds to the lowest frequency that can be generated &
analyzed. It defines the spectral resolution of t he FFT and is calculated by following formula.
∆f
Sampling 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 integ ral multiple of ∆f m ay 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) t hat actually build the multitone signal.
•
Even bins
are all the bins (freq uencies) that emerg e from Equati on 3, i.e. the f requencies
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 freq uency 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
f
kHz may be displayedmax *=≤∆
∆
20
20
Equation 5 Maximum Signal Bin Frequency
Besides the above equations there are no other constraint s for the definition of a multitone
signal. This means you can use any bin representing a fr equency below or equal to 20kHz
as a signal bin. I t is up to the operator what the intention of t he 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 - of fers a special feature that allows to optim ize the phases of any
multitone signal. The results can be loaded dir ectly from or back into the
>@9 Generator.
Low Crest factors ar e important for two reasons. First , the peak level of the m ultitone signal
raises the necessary input range for the analysis and ther eby reduces sensitivity for the lowlevel 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, dist ortion products m ay appear over the entire
band due to the fact that each signal bin produces harm onics and intermodulates with other
signal bins. The strict separation bet ween harmonic distortion and inter modulation cannot be
guaranteed, since at certain signal bins some intermodulation products and harmonic
frequencies may fall to gether, thus influencing t he Distortion as well as the SINAD results..
However, a multitone signal comes much closer to a "r eal-world“ signal than any single tone
test signal. T he results are in qualitative ter ms 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 t o conventional analyzers.
Please refer to the corresponding applicat ion 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 paramet er 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 Durat ion
(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 (f
min
) 1 (93.8 Hz)
Bin_Max (f
max
) 213 (19.969 kHz)
Table 2 Signal Parameter with Blocklength 512 @ fs=48kHz
0 0.005 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
0 0.005 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
>@9
Multitone Audio Test System
User Manual
V 3.32 21 / 71
Blocklength 1024
Frequency spacing ∆f 46.875 Hz
Analyzer resolution 23.4375 Hz
Bin_Min (f
min
) 1 (46.9 Hz)
Bin_Max (f
max
) 426 (19.969 kHz)
Table 3 Signal Parameter with Blocklength 1024 @ fs=48kHz
Blocklength 2048
Frequency spacing ∆f 23.4375 Hz
Analyzer resolution 11.71875 Hz
Bin_Min (f
min
) 1 (23.4 Hz)
Bin_Max (f
max
) 853 (19.992 kHz)
Table 4 Signal Parameter with Blocklength 2048 @ fs=48kHz
Blocklength 4096
Frequency spacing ∆f 11.71875 Hz
Analyzer resolution 5.859375 Hz
Bin_Min (f
min
) 2 (23.4 Hz)
Bin_Max (f
max
) 1706 (19.992 kHz)
Table 5 Signal Parameter with Blocklength 4096 @ fs=48kHz
Blocklength 8192
Frequency spacing ∆f 5.859375 Hz
Analyzer resolution 2.9296875 Hz
Bin_Min (f
min
) 4 (23.4 Hz)
Bin_Max (f
max
) 3413 (19.998 kHz)
Table 6 Signal Parameter with Blocklength 8192 @ fs=48kHz
>@9
Multitone Audio Test System
User Manual
22 / 71 V 3.32
Generator
>@9 comprises a completely independent two-channel 16bit arbitrary g enerator. The digital
section has its own high level microprocessor enabling the system to react flexibly to
external events, communicate with various interfaces and reprog ram the sample counter f or
the arbitrary generator
Block Diagram
MEM 1
MEM 2
MEM 3
MEM 4
ARBITRARY
LOGIC
LED INDICATORS
IEEE-488
INTERFACE
18 BIT D/A CONVERTER
18 BIT D/A CONVERTER
AMP
IMPED.
MUTE
IMPED.
MUTE
AMP
ISOLATION
ISOLATION
CPU
Fig. 16 Block Diagram Generator
Digital Section
The CPU reads the samples out of a non-volatile memory. The memory block provides
capacity for four independent test signals, each with 16 bit resolution and any length def ined
in Table 1. Space is also provided for the header of each signal. The master clock is derived
from a high precision crystal.
Analog Section
The two-channel analog output signal behind the D/A convert ers is fed into a reconstruction
filter, cutting off all freq uencies above 20kHz. On its way the signal also passes through an
electrical isolation to keep the complete analog output section floating. The programmable
output amplifier of fers a balanced signal with 150Ω output impedance (unbalanced 75Ω) at
any level in steps of 0.1dB between -60dBVp to +20dBVp.
Analyzer
The >@9 analyzer consists of a two channel analog input stage, prepar ing the input signals
for the conversion into digital format. With the converted signals an FFT analysis with the