SIST EN 61237-4:1999

Broadcast video tape recorders - Methods of measurement -- Part 4: Analogue audio performance measurements

Describes methods of measurement and special test signals for the analogue audio part of equipment mainly dedicated to recording reproduction of TV signals on mangetic tape on reels or in cassettes. Is applicable to acceptance tests, performance comparison and, as far as possible, to routine checks.

Videobandgeräte für den Rundfunk - Meßverfahren -- Teil 4: Messung der Leistungskennwerte für analoge Tonsignale

Magnétoscopes de radiodiffusion - Méthodes de mesure -- Partie 4: Mesure des caractéristiques audio-analogiques

Décrit les méthodes de mesure et les signaux d'essai particuliers pour la partie audio-analoguique du matériel principalement dédiée à la lecture d'enregistrement de signaux de télévision sur bande magnétique en bobine ou en cassette. S'applique aux essais d'acceptation, aux comparaisons de performances, et autant que possible aux esais de routine.

Broadcast video tape recorders - Methods of measurement -- Part 4: Analogue audio performance measurements (IEC 61237-4:1997)

General Information

• Status: Published
• Publication Date: 31-Mar-1999
• ICS: 33.160.40 - Video systems
• Technical Committee: AVM - Audio, video and multimedia systems and equipment
• Current Stage: 6060 - National Implementation/Publication (Adopted Project)
• Start Date: 01-Apr-1999
• Due Date: 01-Apr-1999
• Completion Date: 01-Apr-1999
• Ref Project: EN 61237-4:1997 - Broadcast video tape recorders - Methods of measurement - Part 4: Analogue audio performance measurements

Standards Content (Sample)

SLOVENSKI STANDARD
SIST EN 61237-4:1999
01-april-1999
Broadcast video tape recorders - Methods of measurement -- Part 4: Analogue
audio performance measurements (IEC 61237-4:1997)
Broadcast video tape recorders - Methods of measurement -- Part 4: Analogue audio
performance measurements
Videobandgeräte für den Rundfunk - Meßverfahren -- Teil 4: Messung der
Leistungskennwerte für analoge Tonsignale
Magnétoscopes de radiodiffusion - Méthodes de mesure -- Partie 4: Mesure des
caractéristiques audio-analogiques
Ta slovenski standard je istoveten z: EN 61237-4:1997
ICS:
33.160.40 Video sistemi Video systems
SIST EN 61237-4:1999 en
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

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NORME
CEI
INTERNATIONALE
IEC
61237-4
INTERNATIONAL
Première édition
STANDARD
First edition
1997-10
Magnétoscopes de radiodiffusion –
Méthodes de mesure –
Partie 4:
Mesure des caractéristiques audio-analogiques
Broadcast video tape recorders –
Methods of measurement –
Part 4:
Analogue audio performance measurements
 IEC 1997 Droits de reproduction réservés  Copyright - all rights reserved
Aucune partie de cette publication ne peut être reproduite ni No part of this publication may be reproduced or utilized in
utilisée sous quelque forme que ce soit et par aucun any form or by any means, electronic or mechanical,
procédé, électronique ou mécanique, y compris la photo- including photocopying and microfilm, without permission in
copie et les microfilms, sans l'accord écrit de l'éditeur. writing from the publisher.
International Electrotechnical Commission 3, rue de Varembé Geneva, Switzerland
Telefax: [phone] e-mail: [e-mail] IEC web site http: //www.iec.ch
CODE PRIX
Commission Electrotechnique Internationale
T
PRICE CODE
International Electrotechnical Commission
Pour prix, voir catalogue en vigueur
For price, see current catalogue

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61237-4 © IEC:1997 – 3 –
CONTENTS
Page
FOREWORD . 5
Clause
1 General. 7
1.1 Scope and object . 7
1.2 Normative references. 7
1.3 Definitions . 9
2 Manual and automatic measurements . 11
3 Procedure of measurement. 11
4 Environmental conditions . 11
5 Measurements on analogue audio baseband recording using bias. 11
5.1 Reproducing performance using calibration tape . 11
5.2 Overall performance using reference tape. 17
6 Measurement on analogue audio recording using frequency modulation (FM audio) . 23
6.1 Reproducing performance using calibration tape . 23
6.2 Overall performance using reference tape. 27
7 Special measurements . 31
7.1 Measurements on FM carrier (unmodulated carrier and deviation) . 31
7.2. Measurements on AGC (amplitude characteristic; attack time; hold time) . 31
7.3 Measurements on switchable noise reduction circuits. 31
7.4 Measurements on non-switchable noise reduction systems (in combination with
a non-switchable AGC) . 37
7.5 Polarity test . 39
Annexes
A Method of measurement for magnetic tape flux . 41
B Bibliography. 47

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61237-4 © IEC:1997 – 5 –
INTERNATIONAL ELECTROTECHNICAL COMMISSION
___________
BROADCAST VIDEO TAPE RECORDERS –
METHODS OF MEASUREMENT –
Part 4: Analogue audio performance measurements
FOREWORD
1) The IEC (International Electrotechnical Commission) is a worldwide organization for standardization comprising
all national electrotechnical committees (IEC National Committees). The object of the IEC is to promote
international co-operation on all questions concerning standardization in the electrical and electronic fields. To
this end and in addition to other activities, the IEC publishes International Standards. Their preparation is
entrusted to technical committees; any IEC National Committee interested in the subject dealt with may
participate in this preparatory work. International, governmental and non-governmental organizations liaising
with the IEC also participate in this preparation. The IEC collaborates closely with the International Organization
for Standardization (ISO) in accordance with conditions determined by agreement between the two
organizations.
2) The formal decisions or agreements of the IEC on technical matters express, as nearly as possible, an
international consensus of opinion on the relevant subjects since each technical committee has representation
from all interested National Committees.
3) The documents produced have the form of recommendations for international use and are published in the form
of standards, technical reports or guides and they are accepted by the National Committees in that sense.
4) In order to promote international unification, IEC National Committees undertake to apply IEC International
Standards transparently to the maximum extent possible in their national and regional standards. Any
divergence between the IEC Standard and the corresponding national or regional standard shall be clearly
indicated in the latter.
5) The IEC provides no marking procedure to indicate its approval and cannot be rendered responsible for any
equipment declared to be in conformity with one of its standards.
6) Attention is drawn to the possibility that some of the elements of this International Standard may be the subject
of patent rights. The IEC shall not be held responsible for identifying any or all such patent rights.
International Standard IEC 61237-4 has been prepared by subcommittee 100B: Recording, of
IEC technical committee 100: Audio, video and multimedia systems and equipment.
The text of this standard is based on the following documents:
FDIS Report on voting
100B/93/FDIS 100B/111/RVD
Full information on the voting for the approval of this standard can be found in the report of
voting indicated in the above table.
IEC 61237 consists of the following parts, under the general title Broadcast video tape
recorders – Methods of measurement:
Part 1: Mechanical measurements
Part 2: Electrical measurements of analogue composite video signals
Part 3: Electrical measurements of analogue component video signals
Part 4: Analogue audio performance measurement
Part 5: Electrical measurements of digital composite video signals and digital audio signals
Part 6: Electrical measurements of digital component video signals and digital audio signals
Annexes A and B are for information only.

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61237-4 © IEC:1997 – 7 –
BROADCAST VIDEO TAPE RECORDERS –
METHODS OF MEASUREMENT –
Part 4: Analogue audio performance measurements
1 General
1.1 Scope and object
This part of IEC 61237 describes methods of measurement and special test signals for the
analogue audio part of equipment mainly dedicated to recording reproduction of TV signals on
magnetic tape on reels or in cassettes.
The allowable tolerances for the rated values for acceptable performance are not given in this
standard, but may be derived from the specifications for the related system i.e. appropriate
publications, manufacturers' specifications, etc.
The necessary reference and calibration tapes are either mentioned in the specific IEC
publication of the equipment under test or included in IEC 61105 and IEC 61295, respectively.
The methods are applicable to acceptance tests, performance comparison and, as far as
possible, to routine checks.
To ensure that the results obtained at a specific time and at a specific place are comparable to
other measurements, it is advisable to specify the test signal, measuring devices and types of
tapes used together with results obtained.
1.2 Normative references
The following normative documents contain provisions which, through reference in this text,
constitute provisions of this part of IEC 61237. At the time of publication, the editions indicated
were valid. All normative documents are subject to revision and parties to agreements based
on this part of IEC 61237 are encouraged to investigate the possibility of applying the most
recent editions of the normative documents indicated below. Members of IEC and ISO maintain
registers of currently valid International Standards.
IEC 60094-3: 1979, Magnetic tape sound recording and reproducing systems – Part 3: Methods
of measuring the characteristics of recording and reproducing equipment for sound on
magnetic tape
IEC 60268-1: 1985, Sound system equipment – Part 1: General
IEC 60268-2: 1987, Sound system equipment – Part 2: Explanation of general terms and
calculation methods
IEC 60268-3: 1988, Sound system equipment – Part 3: Amplifiers
IEC 60268-8: 1973, Sound system equipment – Part 8: Automatic gain control devices

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61237-4 © IEC:1997 – 9 –
IEC 60386: 1972, Method of measurement of speed fluctuations in sound recording and
reproducing equipment
IEC 60602: 1980, Type B helical video recorders
IEC 60651: 1979, Sound level meters
IEC 61041-1: 1990, Non-broadcast video tape recorders – Methods of measurement – Part 1:
General video (NTSC/PAL) and audio (longitudinal) characteristics
IEC 61041-3: 1993, Non-broadcast video tape recorders – Methods of measurement – Part 3:
Audio characteristics for FM recording
IEC 61105: 1991, Reference tapes for video tape recorder systems
IEC 61213: 1993, Analogue audio recording on video tape – Polarity of magnetization
IEC 61260: 1995, Electroacoustics – Octave-band and fractional-octave-band filters
IEC 61295: 1994, Calibration tapes for broadcast VTRs
ITU-R Recommendation BS 468-4: 1990, Measurement of audio-frequency noise voltage level
in sound broadcasting
ITU-R 798-2: 1990, Simulated programme signals
1.3 Definitions
For the purpose of this part of IEC 61237, the following definitions apply:
1.3.1 reference level: Value of signal level defined in the relevant system IEC publication as
remanent magnetic short-circuit flux level on the tape, for example 90 ± 5 nWb/m r.m.s. for
625-50 systems in IEC 60602. Method of measurement is given in annex A of this standard.
1.3.2 crosstalk attenuation or track separation: In multi-channel equipment, signals in one
channel can break through into another channel in an attenuated and distorted form.
Particularly when two adjacent tracks are used or two adjacent channels in the same head
stack are operated simultaneously in different modes for example record and reproduction,
impairments can arise. To make matters worse, beside these audio tracks additional
longitudinal tracks are present on a video tape for example control track and time and control
code track.
The influence of a signal in one channel to another channel can be described in terms of
crosstalk attenuation or track separation.
1.3.3 polarity of the audio signal: An audio signal is deemed to be positive when it results in
an increase in the acoustic pressure on the microphone diaphragm, and thus in the
displacement of the diaphragm towards the rear (see IEC 60268-2).
1.3.4 conservation of polarity on magnetic tapes: To obtain an optimal audio reproduction
it is necessary to make sure that a backward movement of the microphone diaphragm leads to
a forward direction of the loudspeaker diaphragm. This should be preserved either during
recording or tape interchange, detailed explanation is given in IEC 61213.

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61237-4 © IEC:1997 – 11 –
2 Manual and automatic measurements
If an automatic measuring device is designed to give reliable results under the special
conditions of television tape recording/reproducing as for example drop-out, jitter, time-base
errors, head switching or partly insufficient head-to-tape contact, a significant improvement in
measuring speed, accuracy and comparability of results can be achieved.
Therefore preference was given to measuring methods which can be carried out by automatic
measuring equipment or which are suitable for automatic measuring techniques.
Except where a distinction is made in particular clauses between manual and automatic
methods of measurement, the measuring procedures given in this standard are valid for both
methods. However, although in the case of automatic measurements the procedure is carried
out automatically by the test signal analyzer, the various steps are described as if they were
performed manually.
3 Procedure of measurement
The measurements shall be carried out by measuring the reproduced signal after recording on
the same machine (best case configuration).
In certain particular cases, if the multigeneration-performance of a TV signal recording system
is measured, the measurements shall be carried out by measuring the reproduced signal after
recording on a different machine (worst case configuration).
If the television tape machine under test is equipped with external controls for example tracking
control, gain control, etc. these controls shall be set to their preset and mid-position
respectively for all measurements.
Before testing the overall performance, the reproducing channel shall be measured by means
of a calibration tape (see 1.1). Attention shall be paid to the manufacturer's manual and
instructions respectively.
4 Environmental conditions
If not otherwise stated, all measurements shall be carried out at the following atmospheric
conditions:
temperature (20 ± 2) °C;
relative humidity (50 ± 2) %;
air pressure 86 kPa to 106 kPa;
conditioning before testing 24 h.
5 Measurement on analogue audio baseband recording using bias
5.1
Reproducing performance using calibration tape
An audio calibration tape according to IEC 61295 or recommended by the manufacturer of the
equipment under test shall be used for measuring the performance of the reproducing chain of
each channel.

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61237-4 © IEC:1997 – 13 –
If adjustable reproduction gain controls are provided on the equipment, they shall be adjusted
to give the reference output level when reproducing the reference recording level.
If adjustable reproduction-equalization controls are provided, they shall be adjusted to give the
closest approximation to the specified reproducing characteristic when reproducing the
frequency response section of the specified calibration tape.
5.1.1 Head adjustment
The 10 kHz tone recorded on the calibration tape is reproduced and the azimuth angle of the
audio heads shall be adjusted for minimum phase error.
The phase difference expressed in degrees between the particular audio tracks shall be
reported.
5.1.2 Reference output level
The reference level section (1 kHz) of the calibration tape is reproduced and the obtained
output level U expressed in decibels shall be reported.
Ref
5.1.3 Maximum programme level
The maximum output level at 3 %* harmonic distortion (see 5.1.5) shall be measured by
increasing the recording input level of the reference frequency to result in an output voltage U
M
giving 3 %* total harmonic distortion.
U
M
The result: 20 log ()dB shall be reported.
10
U
Ref
5.1.4 Amplitude versus frequency flatness (frequency response)
The frequency response section of the calibration tape shall be reproduced, and the output
level at each frequency shall be measured. The ratio between the output level of each
frequency and the output level of the 1 kHz reference frequency expressed in decibels shall be
reported or plotted in graph form within the specified frequency range. Maximum deviations
from a flat frequency response shall be indicated.
5.1.5 Harmonic distortion
For the measurement of harmonic distortion, reference shall be made to clause 22 of
IEC 60268-3.
The measurement can be made by means of a selective voltmeter, which measures the
amplitude of each spurious spectrum line generated by the distortion process. The preferred
method, however, makes use of a distortion meter, which measures the total harmonic
distortion.
5.1.6 Signal-to-noise ratio
The reference level section of the calibration tape shall be reproduced to obtain the reference
output level U . Then the zero input section shall be reproduced and the output voltage U
Ref N
shall be measured via the filters specified below and the signal-to-noise ratio (20 log
10
U /U ) in dB is reported.
Ref N
___________
*
In some countries the maximum output level is specified at 1 % harmonic distortion.

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61237-4 © IEC:1997 – 15 –
5.1.6.1 Unweighted
Use the wideband filter specified in 6.1 of IEC 60268-1.
5.1.6.2 Weighted
Use the A weighting filter specified in IEC 60651.
NOTE – If necessary, values of signal-to-noise ratio using the psophometric ITU-R curve with quasi-peak
detection may be given in addition (see ITU-R Recommendation 468).
5.1.7 Crosstalk attenuation/track separation
For the definition see 1.3.2 or clause 8 of IEC 60268-2.
During reproduction of the specified section of the calibration tape the outputs of channel A and
channel B shall be measured to obtain the values of the wanted signal (U ) and the unwanted
A
signal (U′ ).
B
The procedure shall be repeated with the operating mode of channels A and B reversed in
order to obtain U and U′ .
B A
The separation is expressed as:
U U
A B
() ()
20 log dB and 20 log dB
10 10
′ ′
U U
A B
NOTE – In practice very few calibration tapes include the appropriate section.
5.1.8 Phase difference between channels
The phase difference between two channels of related information (for example stereo)
resulting from variations in perpendicularity of the head gap to the direction of tape travel.
After winding and rewinding on the equipment under test, the azimuth section (10 kHz) of the
calibration tape shall be reproduced for two related channels via an oscilloscope in chop mode.
Channel 1 shall be used to trigger the time base. The maximum movement of the untriggered
trace 2 (t ) with respect to the triggered trace 1 (t ) shall be observed.
2 1
Peak-to-peak time difference (t – t ) shall be the maximum movement observed of the
2 1
untriggered trace on the oscilloscope.
The phase difference is defined as:
Δϕ = 360° f Δt
azimuth
where
f is equal to the frequency 10 kHz
azimuth
Δt is the peak-to-peak time difference (t – t )
2 1
NOTE – Care shall be taken to ensure that the phase difference is less than 180°. This can be checked by
reproducing the lower frequencies of the calibration tape.

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61237-4 © IEC:1997 – 17 –
5.2 Overall performance using reference tape
NOTE – The measurements described in this subclause are applicable to equipment without AGC. For
equipment with AGC, see IEC 61041-1 and IEC 61041-3.
5.2.1 Bias adjustment
The reproducing channel controls which are set according to 5.1 shall not be subsequently
readjusted.
The audio bias current shall be adjusted according to the manufacturer’s recommendation. If
no manufacturer’s information is available, the following methods may be used, but may not
give optimum results for tapes with thin magnetic coatings.
a) A 10 kHz tone (6,3 kHz for U-Matic) at reference level shall be fed to the input of the
recorder. The record mode shall be selected and the bias setting shall be increased in small
steps, starting from a setting well below the expected operational setting. If the recorder
does not have a simultaneous reproduction facility, a note of the bias control position or
amplitude of the bias waveform shall be taken, together with the tape elapsed time for each
change of setting.
The output level shall be measured either from the output of the simultaneous reproduction
channel or by rewinding the tape and reproducing the recording.
The level will peak at a certain bias setting and it will then slowly decrease as the bias is
further increased.
The bias level is set to a value slightly above the value corresponding to peak output so that
the reproduction output is 1,5 dB below the peak.
b) The audio bias current shall be given by (a + c)/2 where a and c are the bias current
values at which the reproduction output at 1 000 Hz is 1 dB below the maximum obtainable
reproduction output (see figure 1).
Output
1 dB
ac
Bias current
IEC  1 237/97
Figure 1 – Bias characteristics

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61237-4 © IEC:1997 – 19 –
5.2.2 Input level necessary to produce the reference output level
The gain control of the record channel shall be so adjusted that a recording of the 1 000 Hz
tone at reference level present at the input of equipment under test will reproduce a
reproducing output signal of the reference output level, with the gain control of the reproducing
channel adjusted as given in 5.1.
5.2.3 Harmonic distortion
A signal of frequency identical to that of the reference level section of the calibration tape shall
be recorded on the reference tape at reference recording level, resulting in reproduction of a
reference output voltage U .
Ref
The voltage U corresponding to the third harmonic component of the output voltage U is
h Ref
measured via a narrow-band filter. Care shall be taken that the filter bandwidth is not so small
as to cause errors due to speed variations. The voltage U is corrected if necessary for the
h
transmission factor of the filter.
U
h
Third harmonic distortion d : 100 %
3
U
Ref
5.2.4 Amplitude versus frequency flatness (frequency response)
Constant amplitude signals, at frequencies corresponding to those on the frequency response
section of the calibration tape, shall be fed to the input of the equipment and shall be recorded
on the reference tape. The constant amplitude shall be adjusted so that the frequency
corresponding to that on the reference level section of the calibration tape shall be recorded to
reproduce at approximately the same level as the frequency response section of the calibration
tape.
The gain and equalization controls shall remain as adjusted according to 5.1 and 5.2.2
respectively.
The recorded reference tape shall be reproduced, and the measured variations in output level
expressed in decibels shall be plotted as a function of frequency within the specified frequency
range in graph form. Maximum deviations from a flat response shall be noted and the
measurement shall be repeated for each channel.
The results of the measurement should, preferably, be presented in graph form. Alternatively,
the maximum positive and negative deviations from a flat response within the specified
frequency range, expressed in decibels, may be quoted for each channel at each relevant
speed.
5.2.5 Signal-to-noise ratio
For the definition see clause 6 of IEC 60268-2.
For all measurements in this subclause, the adjustable reproducing gain and equalization
controls (if any) shall be set as determined in 5.1 and the adjustable record gain and
equalization controls (if any) shall be set as determined in 5.2.2.
An input signal (see 5.2.3) is recorded on the reference tape and reproduced, resulting in a
reference output voltage
U .
Ref
With the recording input terminated by the rated input impedance an input signal of zero e.m.f.
recorded on the reference tape shall be reproduced via the filters specified below and the
output voltage U corrected, if necessary, for the transmission factor of the relevant filter at the
N
relevant frequency shall be measured.
5.2.5.1 Unweighted
Use the wideband filter specified in 6.1 of IEC 60268-1.

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61237-4 © IEC:1997 – 21 –
5.2.5.2 Weighted
Use the A weighting filter specified in IEC 60651 (see 6.2 of IEC 60268-1).
NOTE – The octave and third-octave filters (if necessary) are specified in IEC 61260. If specially requested, the
psophometric ITU-R curve according to ITU-R Rec. 468 (see 6.2.2 of IEC 60268-1) with quasi-peak detection
may be used in addition (see c) below).
Results:
U
Ref
Signal-to-noise ratio: 20 log ()dB
10
U
N
a) Unweighted signal-to-noise ratio: a single figure is quoted.
b) Weighted signal-to-noise ratio: a single figure is quoted.
c) Octave and third-octave signal-to-noise ratio: a graph showing the ratio as a function of
frequency.
5.2.6 Recorded transients (clicks and plops)
Since most VTRs are used for electronic editing, the noise transient caused when an audio
channel changes from the reproduction to the record mode and vice versa can be an important
impairment.
This impairment shall be measured by putting the audio channel under test into the record
mode without an input signal for approximately 2 min. When this recording is reproduced the
recorder is switched between the reproduction and record modes approximately every 10 s,
again with no signal input.
The level of the transients recorded on the tape at the "in" and "out" points of this sequence
shall then be measured using the same measuring equipment as for signal-to-noise ratio
measurement. The measured levels shall be referred in decibels to the reference level (U ).
Ref
5.2.7 Crosstalk attenuation/track separation
For all this measurements the adjustable gain and equalization controls shall be set as
determined in 5.1 (reproduction channel) and 5.2.2 (record channel) respectively.
Constant amplitude signals at frequencies corresponding to those of the frequency response
section of the specified calibration tape shall be fed to the input of channel A of the equipment
and shall be recorded on the specified reference (subreference) tape. The constant amplitude
shall be adjusted so that the frequency corresponding to that on the reference level section of
the specified calibration tape is recorded to reproduce approximately the same level as the
frequency response section of the specified calibration tape.
At the same time the neighbouring channel B shall operate under the same conditions as those
intended for its subsequent use. Thus, in the case of a stereophonic pair, for example, channel
B shall be terminated by the rated input impedance with no input signal while in the record
mode. The recorded tape shall be reproduced in the normal manner. The third-octave filters
specified in IEC 61260, whose mid-band frequencies correspond to those of the recorded
signals shall be inserted between the output of the equipment under test and the measuring
system. For each frequency the output from channel A for wanted signal (U ) and the output
A
from channel B for unwanted signal (U′ ) shall be measured.
B
The procedure shall be repeated with the operating mode of channels A and B reversed in
order to measure U and U′ .
B A

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61237-4 © IEC:1997 – 23 –
The separation is expressed as:
U U
A B
() ()
20 log dB and 20 log dB
10 10
′ ′
U U
A B
5.2.8 Wow and flutter
Speed fluctuations shall be measured and expressed in accordance with the requirements of
IEC 60386.
5.2.9 Holes and overlaps
A 4 kHz tone at reference level shall be recorded for approximately 5 min and then a 10 s
sequence of 1 kHz tone at the same level shall be inserted. The amplitude variations and their
duration can then be examined by using a storage oscilloscope. The "in" and "out" points can
be clearly identified by the two frequencies used (see also ITU-R Report 798).
5.2.10 Erasing attenuation
For this measurement, the adjustable reproducing gain shall be set as determined in 5.1.
A signal of frequency identical to that of the reference level section of the calibration tape shall
be recorded on the reference tape at reference recording level resulting, on reproduction, in a
reference output voltage U .
Ref
After an interval of 5 min, the recorded signal shall be erased on the equipment under test by
recording a signal of zero e.m.f. while the adjustable record gain control (if any) shall be set to
minimum.
The erased section of the tape shall be reproduced immediately, and the residual output
voltage U shall be measured via a narrow band filter to prevent errors due to noise. Care shall
r
be taken that the filter bandwidth is not so small as to produce speed variations.
The output voltage U is corrected, if necessary, for the transmission factor of the filter at the
r
relevant frequency.
U
Ref
()
Signal-to-erased signal ratio: 20 log dB
10
U
r
5.2.11 Overall channel unbalance
The overall channel unbalance is the difference expressed in decibels of the output levels of
two or more channels when recording and reproducing a signal identical to that of the
reference level section of the specified calibration tape. The output levels shall be measured in
accordance with the
...