Application Note
Introduction to
RAPIDRAPID-TEST
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RT-2M / RT-2X
Introduction to Rapid Test
ABSTRACT
With the RAPID-TEST instruments, NTI offers a series of powerful multitone
analyzers for an extremely fast, yet precise audio performance analysis. Each
type of the series allows the 2-channel analysis of frequency response,
distortion, noise, phase and crosstalk within a minimum of time.
GENERAL INFORMATION
Multitone Signal Analysis
Conventional audio test sets normally transmit single sine waves for signal analysis.
On the other hand, RAPID-TEST generates and analyses multitone signals, i.e. a
mixture of several sine waves with different frequencies. Displayed on an
oscilloscope, a multitone signal almost resembles noise, while on a spectrum
analyzer the single frequencies become visible.
Fig 1 Time Plot of 3-Freq. Multitone Signal
Fig 2 Spectrum of 3-Freq. Multitone Signal
One major advantage of multitone signals is that they correspond much closer with
real world signals like human speech or music than any single sinusoidal wave
(especially when testing data reducing devices).
Furthermore, since several audio parameters may be measured in one step lasting
only fractions of a second, all applications where time is a bottleneck profit from the
enormous analysis speed with multitone signals.
In practice, multitone signal analysis ideally fits for virtually any application where
audio transmission characteristics of a component, line or system shall be evaluated.
Please notice, that RAPID-TEST is available either with analog-only or analog &
digital (ISDN) in-/outputs.
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Typical Applications of RAPID-TEST
RAPID-TEST allows measurements of Level, Distortion, Noise, Crosstalk and Phase
of received multitone bursts. These features may be used e.g. in following
applications.
• Quality Control of (cellular) phones covering Receive, Transmit, Ringer and
Speaker testing
• Analysis of stationary DTMF (Double Tone Multiple Frequency) signals
• Loudspeaker evaluation in a production line
• High-speed line testing in telecom environments
• Automated measurements of broadcast networks
• Satellite communication testing.
Consequently, typical customers of RAPID-TEST are (cellular) phone manufacturers,
high volume audio device manufacturers (e.g. CD players, tape recorders, mixers,
microphones, loudspeakers, modems, PC sound cards etc.) broadcast and telecom
companies, studios, satellite network operators etc.
Mode of Operation
For any multitone burst transmission and measurement of the results, a multitone
generator & analyzer is required, as they are provided in every RAPID-TEST unit.
However, it is also possible that two units are located remotely or to use an external
generator (e.g. a cellular phone) and to analyze its signal with RAPID-TEST.
Next, the multitone signal has to be defined, comprising the frequencies (up to 31) to
be transmitted. These frequencies, together with additional signal components, form
the multitone burst, which is transmitted through the device under test (DUT).
In detail, a RAPID-TEST generated multitone signal has a typical duration of typ.
250-960ms and consists of
1. a coded signal, called trigger, which tells any listening analyzer that a multitone
burst is on the way.
2. a synchronization block which allows the analyzer to adjust itself onto the
generator clock.
3. the multitone signal to be analyzed, which may be repeated within the burst up to
5 times, if required.
In case of externally generated signals, neither trigger nor synchronization block are
necessary. However, in this mode level analysis is possible only (no distortion, noise,
crosstalk, phase).
As soon as the multitone burst is received by a listening RAPID-TEST, it is analyzed
in order to evaluate the characteristics of the transmission path.
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Introduction to Rapid Test
Following picture provides a good overview on the RAPID-TEST mode of operation.
Fig 3 RAPID-TEST Mode of Operation
Control Software
Depending on the use of RAPID-TEST, different software solutions are available
from NTI free of charge.
• RT-EVAL was designed for evaluation purposes, i.e. for an easy-to-understand
lead-in into running RAPID-TEST, but also provides a code generator to support
the integration of the unit into an automated environment.
®
®
• The LabView or LabWindows driver libraries, running with GPIB interface
boards from National Instruments™, ease the programming under the respective
language.
If you are in doubt about how to integrate RAPID-TEST into your application, ask
your next NTI representative, he will assist you in finding an optimal solution for your
demands.
Communication Interface
Due to performance reasons, the communication between RAPID-TEST and the
host controller is done through an IEEE-488 parallel interface.
• This IEEE interface (GPIB) allows to take full advantage of the speed of a
multitone signal analysis
• Furthermore, IEEE interfaces allow to control up to 31 instruments simultaneously
from a single PC.
Additionally, an RS232 serial interface allows to download new firmware versions to
the instrument, or even to control the unit.
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APPLICATION EXAMPLES
1 Quality Control of (Cellular) Phones
Goal
Evaluation of the audio transmission characteristics of analog or ISDN
phones, including phone-specific signal analysis (ringer, DTMF keys etc.).
Set-Up
• Connect the RAPID-TEST output to the input of the cellular phone.
• Connect a RF-demodulator to input of RAPID-TEST.
Fig 4 Standard Phone Test
Procedure
• Define a multitone signal in the telecom frequency range (typically
300Hz, 1kHz, 3kHz).
• Transmit the burst through the phone and RF-demodulator back to
RAPID-TEST.
• Compare the processed data with the specified tolerances.
Hint
Apply the same setup for Receive tests of phones, however with the
input of RAPID-TEST connected to the phone earpiece and the output
of RAPID-TEST connected to the RF-modulator input.
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2 Analysis of Externally Generated (Multitone) Signals
Goal
Electroacoustic analysis of signals, generated by an external system as
e.g. a cellular phone (alert ringer, DTMF tones), regardless whether these
signals are of single or multitone type.
In this mode, the analyzer module of RAPID-TEST is used only.
Set-Up
• Connect input channel(s) of RAPID-TEST to the external signal
source.
• Optionally, a device under test (DUT) may be inserted into the signal
path between the external generator and RAPID-TEST analyzer.
Fig 5 External Signal Analysis
Procedure
• Define a (multitone) signal on the external generator.
• Adjust the basic RAPID-TEST analyzer settings (blocklength, trigger
etc.) according to the expected signal.
• Start measurement and analyze the signal, received by RAPIDTEST.
Hint
It is also possible to use any consumer product (e.g. phones) as signal
source instead of the indicated test instrument.
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3 Evaluation of Loudspeakers / Microphones
Goal
Measurement of the electroacoustic parameters (frequency response,
distortions, noise, phase shift, crosstalk) of a microphone or speaker.
Set-Up
• Install an (active) loudspeaker and a precision microphone with known
characteristics at defined positions in an anechoic chamber.
• Connect the output of RAPID-TEST to the loudspeaker and the input
to the microphone
Fig 6 Microphone Test
Fig 7 Loudspeaker Test
Procedure
• Define a multitone signal in the frequency range of interest.
• Measure all audio parameters of interest and store the results as
reference.
• Install the transducer to be measured instead of the reference
(position must be identical!) and repeat the measurement.
• Calculate the difference between the result of the second test to
your reference data in order to establish the characteristics of your
DUT.
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4 Arbitrary Signal Generator
Goal
Definition and generation of arbitrary signals, which may either be
transmitted for a certain number of times or endlessly.
In this mode, the generator module of RAPID-TEST is used only.
Set-Up
• Connect output channel(s) of RAPID-TEST to the device under test
(DUT).
Fig 8 RAPID-TEST as Arbitrary Signal Generator
Procedure
• Define a (multitone) signal on the RAPID-TEST generator.
• Send the signal each desired time or repetitively.
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5 Transmission Line Testing
Goal
To measure long distance transmission lines, the output of the sending
RAPID-TEST must be connected to the base station of the transmission
line. The receiving RAPID-TEST (also several analyzers are allowed) and
their host PCs may be located anywhere you like.
Set-Up
• Define a multitone signal and feed it through the transmission line.
• Arm the listening RAPID-TEST units and gather the measured data
from their host PCs (e.g. through a Modem link).
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Fig 9 Transmission Line Test
Please notice that for radio transmission tests, the broadcast program must be
interrupted shortly to introduce the multitone burst.
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RAPID-TEST PRODUCT OVERVIEW
GPIB Board from National Instruments™+ RT-EVAL or LabWindows CVI or
LabView driver library or application-specific Program (C, BASIC etc.)
IEEE 488
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R T - IM
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RAPID-TEST
Application Notes
RT-1M A pplication
RT-1M A pplication
Get Familiar with
Writing Code
Cellular Phone
Testing
RT-1M A pplication
RT-1M A pplication
Comparing
Conventional vs.
Multitone Testing
Speakers &
Microphones*
(ask your local NEUTRIK
representative for a copy)
RT-1M A pplication
Introduction
*: to be released
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