IEC 61237-4:1997 pdf download – Broadcast video tape recorders -Methods of measurement – Part 4: Analogue audio performance measurements

IEC 61237-4:1997 pdf download – Broadcast video tape recorders -Methods of measurement – Part 4: Analogue audio performance measurements.
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 lEG 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 specilic 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 chaiacteristics of recording and reproducing equipment for Sound Ofl magnetic tape
IEC 60268-1:1985, Sound system equipment — Part I: General
IEC 60268-2: 1987, Sound system equipment — Part 2: Explanation of general terms and calculation methods
IEC 60268-3: 1988, Sound system equipment — Parr Amplifiers
lEG 60268-8: 1973, Sound system equ,pmen: — Part 8: Automatic gain control devices
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 lEG 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 lEG 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.