User manual | 1GA21_1E

Measurements on CD Players
using the Audio Analyzers
UPL or UPD and the
Audio Test Disc UPA-CD
Application Note 1GA21_1E
Klaus Schiffner, Marco Brusati, 3/95
Rteplaces 1GPAN21E
Subject to change
Products:
Audio Analyzer UPL
Audio Analyzer UPD
Contents:
1.
Conclusion
2.
Introduction
3.
3.1
3.2
3.3
3.4
3.5
Preparation and Starting the Application Software
Required Instruments and Accessories
Software Installation
Starting the Application Software
Configuring the Application
Converting the Setups after Firmware Updates
4.
Operating Concept
5.
5.1
5.2
Measurement Procedures
Measurement Standards
Test Setup
6.
6.1
6.2
6.3
6.4
6.5
6.6
6.7
6.8
6.9
6.10
6.11
6.12
Measurements
Reference Output Voltage and Channel Asymmetry
Frequency Deviation
Signal-to-Noise Ratio
Dynamic Range
Level Nonlinearity
Frequency Response
Distortion
Phase Difference
Crosstalk
Intermodulation Distortion
Output Polarity
Tracking Error
7.
7.1
7.2
7.3
7.4
Subsequent Processing of Measurements
Change of Task Universal Sequence Controller / manual operation
Printout
Restarting the Measurement
Interruption or Continuing a Measurement
8.
Terminating the Application
1.
Conclusion
To analyse the quality of CD players, lots of measurements have to be done. This application note
presents a program, which combines these measurements to an automatically running sequence and
gives a printout of the results. A test CD is used for generating the test signals. Here the Audio Test Disc
UPA-CD from Rohde & Schwarz is used, which holds all required signals in a sequence permitting
automatic measurements to be carried out, without the need of controlling the CD player. In addition, this
application note explains the measurements and informs about the different standards.
2.
Introduction
With the Audio Analyzers UPL and UPD we have measuring instruments which are able to carry out
practically all necessary audio measurements on analog and digital interfaces. In addition to single
measurements, whole test sequences can be performed automatically with the aid of the Universal
Sequence Controller UPL-B10 respectively UPD-K1, which is available as an option. The option is used
in the present Application Note. With the aid of the Universal Sequence Controller also customized
program functions not provided in the audio analyzer can be performed. As an example the converter
nonlinearity is represented as an offset with reference to the ideal characteristic.
Operation of the universal sequence controller programs can be matched to the softkeys of the analyzer
display in appearance and functionality. This has been done for the described application.
The application uses a BASIC program for automatic measurements on CD players. Results can be
printed out or stored for further processing.
3.
Preparation and Starting the Application Software
3.1.
Required Instruments and Accessories
As regards the hardware, a basic model of the Audio Analyzer UPL or UPD will be sufficient to carry out
all the measurements on analog interfaces described below. Normally, these measurements will cover all
requirements. Although the data stream at the digital interfaces can be analyzed, it only provides
information on the signal recorded on the CD which, however, is not changed by the CD player. Merely a
protocol analysis of the auxiliary data transmitted in the digital data stream could prove to be of interest.
This analysis can be carried out with the aid of the option UPD-B2 for the UPD, respectively the options
UPL-B2 and UPL-B21 for the UPL.
In any case an external keyboard will also be required.
A test CD is used for generating test signals. Basically, any test CD could be used, but in this case the set
would be required to select the correct tracks for the measurement in question. This disadvantage can be
avoided by using the Audio Test Disc UPA-CD from Rohde & Schwarz. It holds all required signals in a
sequence permitting automatic measurements to be carried out. Apart from starting the CD player no
other action is required during the play of the CD. In addition to the signals for testing CD players, the CD
from Rohde & Schwarz comprises signals and signal sequences for measuring other audio components,
for instance tape recorders. The Audio Test Disc UPA-CD can be obtained from Rohde & Schwarz under
the Order No. 852.8400.02.
The BASIC programs required for an automatic test run are stored on a floppy disk to be obtained from
your local Rohde & Schwarz sales organization.
UPL/UPD should meet the following software requirements:
•
•
•
•
3.2.
UPD firmware version 3.00 or higher,
UPL firmware version 1.00 or higher,
Universal Sequence Controller built-in,
Analyzer configured with 64-Kbyte program memory and 64-Kbyte data memory for Universal
Sequence Controller (select setting 5 using configuration tool UPLSET/UPDSET).
Software Installation
The application software is installed with the aid of installation program CDINST.BAT which is on the
supplied floppy disk:
•
•
•
•
•
Quit the UPL/UPD software by pressing the SYSTEM key or Ctrl+F9 on the keyboard
Insert supplied floppy disk
Select disk drive (enter A:)
Call up the installation program (enter CDINST)
Return to UPL/UPD program
Program CDINST generates the directory C:\CDPLAYER in the UPL/UPD (if it does not yet exist) and
copies the BASIC programs and the setups required for the application into this directory.
3.3.
Starting the Application Software
The application program is run with the aid of the universal sequence controller. After the UPL/UPD
program has been started, operation is switched to the universal sequence controller by means of key F3
(on the external keyboard).
Before switching over to the sequence controller make sure that the logging function is switched off. This
is indicated by the message "logging off" displayed at the bottom righthand end of the screen. With the
logging function on, commands entered during manual operation would be appended to the program and
take up additional memory capacity. The logging mode is switched off by pressing key F2 on the external
keyboard.
Application programs are to be called up via path C:\CDPLAYER as all program modules and setups are
searched for in this path which may be changed either
• at the UPL/UPD level with the "Working Dir" command in the FILE panel,
• by calling up one of the setups required for measurements on CD players,
• at the UPL-B10/UPD-K1 level by means of the BASIC command line
UPD OUT"MMEM:CDIR\CDPLAYER",
• via the SHELL by entering CD CDPLAYER and pressing EXIT,
• at the DOS level by entering CD CDPLAYER.
The program disk comprises the BASIC program CDTEST.BAS for measurements at the analog
interfaces of CD players. It is loaded and started by entering:
• LOAD"CDTEST"
• RUN
Loading and starting is also possible by means of the softkeys displayed at the bottom of the screen when
the Universal Sequence Controller software is called up.
3.4.
Configuring the Application
Measurements are carried out with a number of setups stored on the application floppy. All setups for
measurements on analog interfaces have the designation
CDA_XXXX.SAC
The code word under XXXX identifies the measurement function, eg "FREQ" stands for frequency
response, "THDN" for THD+noise measurement, "CROS" for crosstalk, etc. Only the "actual setups" are
used. Contrary to the "complete setups" they comprise settings for analyzer ANLG 22kHz used in the
application as well as settings made in the DISPLAY, FILE and OPTION panels. The advantage of actual
setups is that they can be called up in a considerably shorter time than complete setups which hold all the
settings.
Upon delivery the setups are configured for printout of measurement results on a "default" printer. This
means, the settings of the printer which have been uses during the last operation of the UPL/UPD will be
used again. The UPL/UPD screen is set to colour display and an external monitor is connected. These
settings may, of course, be adapted to user requirements by modifying the settings in the OPTION panel.
Customers may wish to make other changes in the individual setups. In this case the respective setups
are called up and after modification stored again under the same name. The following modifications can
be made:
• Entry of a comment in the graphics display ("Comment" in the DISPLAY panel)
• Defining tolerance curves/values ("Limit Check" in the DISPLAY panel)
• Selection of settings to be displayed in the STATUS panel (marking)
IMPORTANT: If others than the above-mentioned settings are changed, a correct run of the software
cannot be guaranteed.
3.5.
Converting the Setups after Firmware Updates
Upon an update of the UPL/UPD firmware, setups may require to be converted. The conversion is carried
out automatically every time the setups are loaded. However, this might extend the loading procedure to
an extent that proper execution of the measurement sequence is no longer possible. For this reason the
setups should be converted and stored before the application software is started. This can be done in two
ways:
• At the DOS level by calling up the converter program
DO_CONV \CDPLAYER.
In this case all setups in the CDPLAYER directory are converted.
• At the UPL/UPD level by loading and restoring every setup after conversion.
IMPORTANT: In setups with READ ONLY, the "r" attribute has to be cleared first (at the DOS level by
means of command ATTRIB -r).
4.
Operating Concept
After starting the program, the user is prompted to enter the information items to be printed on the test
report. These include the type designation of the CD player to be tested and the name of the person
carrying out the test. Date and time will be taken automatically from the analyzer's system clock.
The display of a list of possible measurements follows. A selection can be made whether an automatic
test sequence or single measurements are to be made. The single-measurement mode is required for
carrying out measurements that are not included in the automatic measurement sequence.
The CONFIG softkey (corresp. to F11) is displayed together with the list of possible measurements.
When it is pressed, a menu is displayed where the units dB or % can be selected. This selection is valid
for THD-N, intermodulation and difference frequency distortion measurements. Measurements are in
most cases carried out at the unbalanced analog outputs of the CD player, but balanced outputs - as are
required for professional CD players - can also be used. The selection can be made in the CONFIG menu
as well.
After the return to the main menu the desired measurement is selected.
This is followed by the request:
Select track X and press PLAY,
"X" being the required track number on the test disc.
The program detects the start of the test CD automatically and begins with the measurements.
Synchronization of individual measurements is also automatic. For synchronization, levels and
frequencies on the CD are evaluated and the measurements are switched accordingly. For
measurements that cannot be exactly assigned when the DUT is faulty, eg for linearity measurements,
short sections with high level or other frequencies are stored on the CD for continuing the test program.
At various stages of the program, sequence softkeys are displayed at the bottom of the screen. With the
aid of these softkeys, which correspond to the function keys on the external keyboard, the measurement
sequence can be changed.
The following functions are available:
GOTO UPD (= F5)
stops the ongoing program and switches to manual operation of the UPL/UPD without terminating BASIC
eg for evaluating a graphics display by means of a cursor or for entering a comment.
STOP (= F7)
interrupts the ongoing measurement. It is followed by
CONT (= F7)
for continuing the measurement.
CONFIG (= F11)
branches to the above-mentioned configuration routine.
HARDCOPY (= F12)
outputs the screen content or measurement results to the interface selected in the OPTIONS panel (for
printer, plotter or file).
5.
Measurement Procedure
5.1.
Measurement Standards
Measurements are in line with the international standard IEC 1096:1992: Methods of measuring the
characteristics of reproducing equipment for digital-audio compact discs, or with the European Standard
EN 61096:1993: Meßverfahren für die Eigenschaften von Wiedergabegeräten für Digital-Audio-CompactDiscs.
The measurements
• max. power consumption
• frequency response with deemphasis and
• access times
are not part of the described sequence. The output polarity measurement is carried out in a slightly
modified way because the test signal specified in the standard is not available on the Rohde & Schwarz
test CD.
Tracking errors are measured in addition to the measurements prescribed by the standards.
5.2.
Test Setup
Audio Analyzer UPL or UPD, a Test Disc UPA-CD and possibly a printer for result documentation are
required.
The output of the CD player for the left channel is to be connected to UPL/UPD test input 1, the right
channel to input 2.
The setup is to be properly earthed for the measurements, eg to avoid hum loops. Since CD players are
normally provided with floating outputs, the inputs of UPL/UPD are grounded by selecting "Common
GROUND" and has already been considered in the application setups.
The printer is connected to the Centronics interface.
6.
Measurements
The following sections describe the measurements in the sequence in which they are carried out in an
automatic test run.
With some measurements a lowpass filter has to be used for eliminating signal components above
20 kHz. At 24.1 kHz the attenuation must be at least 60 dB, above 44.1 kHz at least 100 dB. The
analyzer ANLG22kHz is used for this application. Up to 22 kHz it features a flat frequency response and
suppresses all higher frequencies. This goes far beyond the IEC 1096 requirements.
Since only audio frequencies between 20 Hz to 20 kHz are evaluated, lowpass filters are required.
However, because of the digital signal processing in the CD player, residues of clock pulses as well as
mixer products and image frequencies inevitably occur. The 44.1 kHz - fs image frequency of the CD
player is more or less suppressed by the built-in anti-aliasing filter, but when it comes to higher
frequencies, where signal and interference frequencies approach each other, an elaborate circuit would
be required for the suppression. In practice such circuit is often left out for reasons of cost. For example,
without additional filtering the distortion measurement would be falsified by the image frequencies. This is
shown by an increase of the distortion factor towards higher frequencies. The lowpass filter ensures that
correct measurement results are obtained.
6.1.
Reference Output Voltage and Channel Asymmetry
During replay of the recorded reference level (at 1 kHz) the rms output voltage of the CD player is
measured in both channels and stored as a reference value for further measurements. The measured
value is indicated in Volt.
At the same time the level difference between the two channels is calculated and displayed in dB.
IMPORTANT: If a volume control is provided on the CD player, it should be set to nominal output
voltage.
With top-quality instruments the level difference should not be much more than 0.1 dB.
6.2.
Frequency Deviation
This measured parameter is also called pitch error. The frequency of the replayed signal is compared to
the rated frequency of the test CD and the difference is indicated in %.
Normally, deviations from the rated frequency are minimal, as the frequency is determined by the
accuracy of the built-in crystal. Measured values are in most cases about 0.1%. In some CD players
greater deviations occur, eg in portable instruments using a simple ceramic resonator instead of a crystal.
With some professional units the replay speed can be varied. In this case the described measurement
can be used for checking the setting range.
6.3.
Signal-to-Noise Ratio
According to IEC 1096, the measured signal-to-noise ratio (to IEC 268-1) is to be determined unweighted
and weighted with an A filter. The measurement is carried out separately in each channel. For the present
application the S/N ratio is also weighted to CCIR 468 as is common for professional equipment.
The ratio of the replayed reference level to the noise level of a replayed digital zero signal is measured.
The test CD contains a digital zero signal, ie no signal is applied to the converter. Mainly the noise of the
analog components and interference coupled into the output amplifiers affect the measurement results.
S/N values of 100 dB and above (with A-weighting) are expected of high-grade CD players.
6.4.
Dynamic Range
Noise and distortion are measured in relation to the recorded reference level. The result is indicated in
dB.
In addition to analog effects such as noise, signal quantization also limits the dynamic range of digital
systems. With the 16-bit linear digitization of the CD, a theoretical dynamic range of approx. 98 dB is
obtained (with an evaluation bandwidth of 20 kHz). CD players with 18-bit or even 20-bit converters
cannot yield a greater dynamic range since the information on the CD is in the form of 16-bit words. What
such converters attain is that the dynamic range is not impaired by additional resolution errors. Since it
can be assumed that the quantization errors of the CD and the converter are not correlated, the
theoretical limit of 98 dB can also be attained by top-class units with 16-bit converters.
For this measurement, IEC specifies a test signal with a level of 60 dB below the reference level. This is
necessary in order to separate the effects of nonlinear distortions (caused by analog circuit sections) and
quantization errors. As the measurement is carried out at low levels of approx. 2 mV, these distortions
have practically no effect.
THD + noise is measured and not all distortion meters are able to measure at such low levels. For this
reason IEC stipulates an amplifier which boosts the level to a value which can also be measured by
simple distortion meters. Audio Analyzer UPL and UPD does not require such auxiliary equipment since it
is able to determine the dynamic range up to far above 100 dB without additional amplifiers.
The result is related to the reference level. This means that the 60 dB by which the signal level has been
reduced must be added to the THD+N values which are referenced to the output signal. This is taken into
account by the present application program.
Before IEC 1096 came into force, the dynamic range was weighted with an A filter. To be able to
compare current measurement results and those of previous measurements, the A-weighted dynamic
range is also specified for the present application.
High-grade CD players attain values of 95 dB and better (measured without A weighting).
6.5.
Level Nonlinearity
The level nonlinearity is the true deviation of the output signal from the level recorded on the CD. This
measurement is frequently specified as converter nonlinearity. The differences between measured and
recorded levels are specified for each measurement step in dB, separately for each channel and for all
test signals up to 90 dB below the reference level at 1 kHz. These measurements are carried out
selectively for suppressing noise and interference.
The Rohde & Schwarz test CD comprises test signals which are first reduced in 10-dB steps and later on
in steps matching those of the bit structure. The signals (0 dB, 2 kHz) inserted between the individual
steps are used for synchronizing the measurement sequence since, in the case of DUTs with a moderate
converter linearity, measured levels are not accurate enough for a reliable step identification.
This measurement, which is so important for testing the fidelity of sound reproduction, shows
considerable differences between the various CD players. While high-quality equipment show linearity
errors of <1 dB up to levels of -80 dB, deviations of more than 10 dB may well occur in the case of
simpler units. A complete suppression of extremely low levels is possible. The measured values for S/N
or the dynamic range can be improved by the intentional reduction or suppression of very small levels.
Therefore these measured values must be evaluated critically whenever high linearity errors are
involved. Figs. 1 and 2 show examples for measurements on high-quality and simple CD players.
Fig. 1: Typical linearity curve of a well-aligned unit
Fig. 2: Linearity curve of a CD player deviating considerably from the rated curve
6.6.
Frequency Response
The output level of the two channels is displayed as a function of frequency.
Variable-frequency or fixed-frequency sweeps may be used for this measurement. More convincing
results are obtained with the variable-frequency sweep. Sweeps from 20 Hz to 20 kHz are used on the
test CD from Rohde & Schwarz and recorded consecutively for the two channels. Thanks to the high
measurement rate of the UPL/UPD, frequency response can be determined with a resolution of 0.01 dB.
Fig. 3: Typical frequency response of a CD player with digital filtering
Normally, the frequency response of even simple CD players is far better than that of analog
components. A wavy response is often shown at higher frequencies and results from the digital filtering in
the CD player (Fig. 3). The higher the number of poles of the built-in filter, the flatter and smoother the
frequency response. In the case of top-class units, the frequency response remains flat below 0.1 dB.
Note that the frequency response is referred to the level at 1 kHz for the respective channel. For this
reason level differences between the two channels, as are measured under section 5.1, cannot be
derived from the frequency response display.
6.7.
Distortion
A measurement of the THD+N value at fixed frequencies between 20 Hz and 20 kHz is prescribed,
including a measurement at 1 kHz.
The test CD from Rohde & Schwarz includes 12 signal frequencies for this measurement and thus meets
this requirement. Measurement results may be displayed in % or dB.
As a result of inadequate anti-aliasing filtering, mixture products occur through mixing harmonics of the
signal frequency with the clock frequency or harmonics thereof. Even at low amplitudes, these products
can be very disturbing. Typical mixture products are generated, for example, from the 1st and the 3rd
harmonics of the signal frequency mixed with the clock frequency. As can be seen from Fig. 4, the
products 24.1 kHz (= 44.1 - 20) and 15.9 kHz (= 3 x 20 - 44.1) occur at a 20-kHz signal frequency.
Fig. 5 shows a typical distortion curve as a function of frequency. The curve shows a slight rise up to
approx. 10 kHz since up to this frequency the 1st harmonic of the signal is measured as well. Above 11
kHz the harmonic is suppressed by the lowpass filter, the distortion drops, but the mixture products
described above cause the curve to increase again.
Top-class CD players achieve a distortion suppression of greater than 90 dB over the entire frequency
range.
Fig. 4: Typical distortion curve showing mixture products at 24.1 kHz and 15.9 kHz
Fig. 5: Example of a distortion curve as a function of frequency
6.8.
Phase Difference
The phase difference between the left and the right channel is measured at various frequencies. IEC
1096 prescribes measurements at 1 kHz and 20 kHz, measurements at other frequencies are voluntary.
In the present application, the phase measurement is carried out in parallel with the distortion
measurement, ie distortion and phase are measured alternately during the test signal run. The result of
the phase measurement is displayed as soon as the THD+N measurement is terminated.
Top-class CD players show a phase difference of less than 0.5°.
Fig. 6: Phase characteristic of a top-class CD player versus frequency
When CD players were introduced for the first time, also units with only one D/A converter operating in
the multiplex mode were used. In the simplest case without oversampling, a phase difference of approx.
82° is obtained at a signal frequency of 20 kHz as a result of the shift in time by half a system clock. The
phase difference can be reduced to about half the value with oversampling and compensation measures.
This "economy configuration" can be identified by the typical rise of the phase angle as a function of
frequency.
IEC 1096 refers to this time offset occurring with players using one converter in the multiplex mode. An
example is shown in the diagram below.
Fig. 7: Phase characteristic of a CD player using one D/A converter only
6.9.
Crosstalk
The level difference between the wanted signal in one channel and the unwanted signal caused by the
wanted signal in the other channel is measured. A measurement is prescribed for both directions at
1 kHz; measurements at other frequencies are voluntary.
In the present application, the crosstalk is measured at 1 kHz, 10 kHz and 20 kHz. Since the crosstalk
level in top-class unit is relatively close to the noise level, the measurement must be carried out
selectively.
Results from 90 dB to better than 100 dB are achieved by top-class CD players.
6.10. Intermodulation Distortion
Intermodulation distortion is the ratio of all intermodulation products referred to the useful signal.
Measuring the intermodulation distortion of CD players is prescribed by IEC 268-1, section 7.2.8. Two test
tones with an amplitude ratio of 4:1 are used for the measurement. Measuring the difference-frequency
distortion to IEC 268-2, section 7.2.11, is voluntary. In this case two test tones of identical level and
spaced by 1 kHz are superimposed.
Contrary to the test frequencies for intermodulation measurements of 60 Hz for the noise and 7 kHz for
the wanted signal specified by IEC 1096, the test CD from Rohde & Schwarz uses a 400-Hz noise signal.
This makes practically no difference for the measurement result. The reason for using the frequency
combination 400 Hz + 7 kHz is that in this case a more simple and accurate measurement can be carried
out with the analog Audio Analyzer UPA. The frequency combination 60 Hz + 7 kHz can be found on
track 42 of the test CD. This test signal can also be used for single-shot measurements with the
UPL/UPD.
Since the sum signal of the wanted and the noise signal must not exceed the dynamic range of the CD, a
low-frequency signal of -2 dB and a high-frequency signal of -14 dB are recorded. When using simple
instruments for measuring the intermodulation, the measurement result for intermodulation suppression is
limited by the quantization noise of the CD player. For this reason and because the value is referred to
the 7-kHz signal, measured values of up to approx. 85 dB are possible. This limitation is avoided in the
audio analyzers UPL and UPD by a selective measurement of intermodulation products, ie independent
from the quantization noise.
Also the difference-frequency distortion at various frequency combinations may be determined by means
of a single-shot measurement. In this case tracks 39 to 41 of the test CD are used. 2nd and 3rd order
intermodulation is measured.
According to IEC 1096, all measured intermodulation values are indicated in %. In the UPL/UPD
indication in dB is also possible.
Top-class CD players achieve an intermodulation suppression of approx. 90 dB and a differencefrequency suppression of approx. 100 dB.
6.11. Output Polarity
The influence of the CD player on the polarity of the output signal is determined by measuring the pulses
on replay.
According to IEC 1096, 0-dB pulses with a width of one data word should be used for these tests. Such
signals are not provided on the Rohde & Schwarz test CD. The purpose of this measurement is to
determine whether pulses recorded with equal phase are output by the CD player in-phase and with
correct polarity. Pulse-inverting channels are to be indicated.
In the present Application Note, a slightly different single-shot measurement is used, which yields the
same results, however.
A pulse inversion can be determined by means of the burst signals on track 47. If the replayed pulse
begins with a positive rise, no inversion is performed.
Here IEC 1096 points out that the tested CD player may be equipped with only one D/A converter in the
multiplex mode. This can be determined by measuring the phase difference as described under 5.8.
6.12. Tracking Error
A test method for determining the behaviour of CD players in the case of defective discs is being
discussed at present by the standardization committees.
The present application also offers a way of measuring the tracking error in addition to all the mentioned
measurements. However, special test CDs with simulated faults are required in this case. Before the test
is performed, the user is prompted by the application program to insert a respective CD. The Test Disc
CDT-016, Order Designation SZZ P1054 from Panasonic, is used in this case. It simulates two different
error sources:
• Surface defects of the CD:
Dirt and scratches on the surface may lead to errors when digital data are read. Such defects are
simulated by painted dots of different diameters.
• Defects of the information layer of the CD
For simulating this error source, certain areas of the information layer inside the CD have been
destroyed.
The response of CD players may be quite different regarding the two types of errors. It is possible for a
CD player to correct one type perfectly and unnoticed by the listener while audible signal changes are
produced when correcting the other. For this reason both tests should be carried for examining both types
of errors.
The information on the CD has redundance so that error handling routines may be able to regenerate the
original code free of errors provided that not more than 1.2 mm of the track is lost. However, not all CD
players are able to cope with incurred errors in that way. Despite an error-free reconstruction it may
happen that correction errors are produced which impair the original signal and generate an audible
clicking noise. In the event that the CD player is not able to retrieve the missing signal, the output signal
of the many CD player is muted for the period of the fault. It may also happen that the servo circuit for
tracking can no longer find the track to be read and the disc gets stuck. Since the above-mentioned
characteristics provide important information on the suitability of a CD player in everyday use, sufficient
importance should be attached to the measurement of the tracking error.
The measurement is based on the fact that even the slightest signal changes become evident by a rise in
THD. Thus the distortion factor is measured and recorded with time whilst the faulty track is running. In
the event of insufficient error correction of the CD player, the periodic reading of the faulty area causes a
peak in the distortion as shown in Fig. 8. A constant, low THD indicates a correctly functioning error
correction (Fig. 9). In the event that the signal of the CD player is briefly muted, the Audio Analyzers UPL
and UPD records a sudden level change. In the diagram muting is shown by gaps in the curve.
A top-class CD player should be able to correct both, surface and information layer errors. In this case the
tracks with the largest interruptions (0.9 mm) are used. Playing other tracks with smaller interruptions can
exactly reveal the error correction capabilities of the DUT.
Fig. 8: Disturbance caused by faulty restoration of missing data
Fig. 9: Faultless error correction
7.
Subsequent Processing of Measurements
Subsequent processing is only possible when single-shot measurements have been carried out. In this
case manual operation has to be selected on the UPL/UPD so that modifications, eg changes in the
graphics display, can be performed.
7.1.
Change of Task Universal Sequence Controller / manual operation
Upon completion of a single-shot measurement, the "GOTO UPD" softkey (F5) is displayed permitting
switchover to manual UPL/UPD operation without the BASIC program being terminated. The program
may still be used for procedures such as
•
•
•
•
•
•
changing the graphics scale,
moving the graphics cursor or switching it on and off,
entering a comment to the graphics display,
configuring the printer interface,
printing a section of the diagram with a modified status panel,
displaying measured values or limit violations in tabular form.
Pressing function key F3 on the external keyboard causes a return to the location in the application
program at which the BASIC program was quit.
This interruption cannot be made during automatic testing of the CD player. Although it would be possible
to stop the program the test CD would continue to run.
7.2.
Printout
After the test sequence has been completed a menu is displayed permitting the whole test report to be
output to a printer or to a memory for storing.
After a single-shot measurement has been carried out, the HARDCOPY softkey (F12) is displayed so that
the screen can be printed if it contains a diagram.
Of course, the hardcopy function can also be activated at the UPL/UPD level. In this case also trace data
or limit violations can be printed.
7.3.
Restarting the Measurement
The application can be restarted any time by entering the BASIC command RUN.
7.4.
Interruption or Continuing a Measurement
The program can be interrupted by pressing the STOP softkey (F5). The softkey label then changes to
CONT so that the measurement can be continued.
8.
Terminating the Application
Pressing the ESC key on the external keyboard or the CANCEL key on the UPL/UPD causes a return to
the previous menu level. Pressing one of these keys at the top level terminates the program, ie by
pressing a key several times the program can be terminated from any menu level.
To avoid the program from being ended inadvertently, a query is displayed prior to the termination of the
program.
The software can be aborted any time by pressing CTRL+BREAK. After the entry of CONT the program
is continued whereas RUN triggers a restart.
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ROHDE & SCHWARZ GmbH & Co. KG P.O.B. 80 14 69 D-81614 München
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Telephone +49 1805 124242 · Fax +49 89 4129 - 3777 Internet: http://www.rsd.de

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