1、BRITISH STANDARD BS4847:1989 IEC386:1972 (Incorporating Amendment No.11988) Method of measurement of speed fluctuations in sound recording and reproducing equipmentBS4847:1989 This BritishStandard, having been prepared under the directionof the Electronic Equipment Standards Policy Committee, was pu
2、blished underthe authority of the BoardofBSI and comes into effect on 31 October1989 BSI 12-1999 First published August1972 Second edition October1989 The following BSI references relate to the work on this standard: Committee reference EEL/22 Draft for comment86/23362DC ISBN 0 580 17630 4 Committee
3、s responsible for this BritishStandard The preparation of this BritishStandard was entrusted by the Electronic Equipment Standards Policy Committee (EEL/-) to Technical Committee EEL/22, upon which the following bodies were represented: British Broadcasting Corporation British Kinematograph, Sound a
4、nd Television Society Council for Educational Technology for the UnitedKingdom Electronic Engineering Association Independent Broadcasting Authority Independent Television Association Sound and Communication Industries Federation The following bodies were also represented in the drafting of the stan
5、dard, through subcommittees and panels: Association of Professional Recording Studios Audio Engineering Society British Tape Industry Association Royal Photographic Society Amendments issued since publication Amd. No. Date of issue CommentsBS4847:1989 BSI 12-1999 i Contents Page Committees responsib
6、le Inside front cover National foreword ii 1 Scope 1 2 Definitions 1 3 Measurement of flutter and wow 1 4 Measuring equipment and methods 1 Appendix A Additional requirements for measuring equipment 5 Appendix B Explanatory notes 5 Figure 1 Weighting curve 3 Figure 2 Dynamic characteristics 3 Figure
7、 3 Example of2-sigma calculation method 4 Table I Weighting factors 2 Publications referred to Inside back coverBS4847:1989 ii BSI 12-1999 National foreword This new edition or BS4847 has been prepared under the direction of the Electronic Equipment Standards Policy Committee and is identical with I
8、EC386:1972 “Method of measurement of speed fluctuations in sound recording and reproducing equipment” published by the International Electrotechnical Commission (IEC), as amended by Amendment No.1 published in March1988. This BritishStandard replaces BS4847:1972, which is withdrawn. For the purposes
9、 of this BritishStandard, any references to IEC page numbers in the text should be ignored. Wherever the word “Recommendation” relating to this publication appears, it should be interpreted as “BritishStandard”. A British Standard does not purport to include all the necessary provisions of a contrac
10、t. Users of British Standards are responsible for their correct application. Compliance with a British Standard does not of itself confer immunity from legal obligations. Summary of pages This document comprises a front cover, an inside front cover, pagesi andii, pages1 to6, an inside back cover and
11、 a back cover. This standard has been updated (see copyright date) and may have had amendments incorporated. This will be indicated in the amendment table on the inside front cover.BS4847:1989 BSI 12-1999 1 1 Scope This Recommendation applies to a method of measurement using the weighted peak techni
12、que. Appendices give explanatory notes concerning flutter and wow measurement as well as details of the measuring equipment. 2 Definitions For the purposes of this Recommendation, the following definitions shall apply: 2.1 flutter undesired form of frequency modulation introduced into the signal by
13、an irregular motion of the recording medium during the recording/reproducing process, at frequencies above10Hz 2.2 wow undesired form of frequency modulation introduced into the signal by an irregular motion of the recording medium during the recording/reproducing process, at frequencies from0.1Hz t
14、o10Hz 2.3 drift slow variation of the velocity of the recording medium during recording and reproducing 3 Measurement of flutter and wow 3.1 A method giving the peak value shall be used for the measurement of flutter and wow for sound recording and reproduction equipment. 3.2 The measurements shall
15、be made at a frequency of3150Hz. 3.3 The measurement shall be made on one element only of the system (either the recorder or the reproducer, but not on both) under such conditions that the flutter and wow in the remaining parts of the system is negligible. 3.4 When this condition cannot be fulfilled
16、, a recorder/reproducer may be measured by recording a3150Hz test frequency and reproducing this recording several times, measuring in each case the total flutter and wow and forming the arithmetic average value of these measurements. Flutter and wow shall not be measured while simultaneously record
17、ing and reproducing. 3.5 The measuring conditions shall always be stated, namely: reproducer only, recorder only or complete recording/reproducing system. 4 Measuring equipment and methods In this clause the response curve shall be as specified in Table I and Figure 1. NOTEAn unweighted response cur
18、ve, flat at least between0.1Hz and200Hz would provide useful additional information about the source of flutter and wow. Tolerances and measuring methods are not specified for the unweighted response curve. 4.1 Method1:2-sigma method (preferred) During a given time interval of at least5s the instant
19、aneous speed deviations are stored in a memory. The instantaneous speed deviations are compared with a threshold%v. The cumulative time within the given time interval for which the instantaneous speed deviations exceed this threshold in a positive or negative direction is calculated. The measuring e
20、quipment searches for that threshold%v ofor which the cumulative time is equal to5 %of the given time interval. The measurement result%v oshall be expressed as a percentage of the average speed. See Figure 3. NOTEWhen the speed deviation follows a Gaussian distribution, the indicated value is equal
21、to twice the standard deviation of the distribution:“2 sigma”.BS4847:1989 2 BSI 12-1999 4.2 Method2 4.2.1 Dynamic characteristics For short unidirectional deviations of the frequency of measurement (rectangular pulses of a duration A) with a repetition rate of1Hz, the meter shall indicate the percen
22、tage B of the reading obtained with a sinusoidal frequency modulation of4Hz having a peak-to-peak deviation equal to the frequency swing of the pulse, that is (see Figure 2,page 3): %f pulse =2%f sin max. The return time shall be such that, when applying pulses of100ms duration with a repetition rat
23、e of1Hz, the meter shall indicate between36% and44% between the pulses. The dynamic characteristic refers to the complete measuring equipment including, weighting network. 4.2.2 Indication of instrument The instrument shall respond to positive and negative speed deviations and its scale shall be cal
24、ibrated in percentage deviation from average speed. The result shall be expressed in percentage deviation from average speed: Since the fall-time of the instrument is not infinite, fluctuations of readings can occur when the speed varies very slowly. In such cases, the maximum reading shall be taken
25、 as the result. 4.3 The method used shall be stated if different from Method1. Table I Weighting factors Frequency (Hz) Response (dB) Tolerances 0.1 0.2 48.0 30.6 from to 0.1 0.2 Hz Hz +10dB 4dB 0.315 0.4 19.7 15.0 from to 0.315 0.5 Hz Hz 4dB 0.63 0.8 1 1.6 2 8.4 6.0 4.2 1.8 0.9 from to 0.54 50 Hz H
26、z 2db 63 100 200 14.2 17.3 23.0 from to 50 200 Hz Hz 4dB Percentage deviation 0.5peak-to-peak speed deviation 100 % average speed - = BS4847:1989 BSI 12-1999 3 Figure 1 Weighting curve Pulse length A (ms) 10 30 60 100 Indication B (%) 21 3 62 6 90 6 100 4 Figure 2 Dynamic characteristicsBS4847:1989
27、4 BSI 12-1999 Figure 3 Example of 2-sigma calculation methodBS4847:1989 BSI 12-1999 5 Appendix A Additional requirements for measuring equipment 1 The measuring equipment should operate within the limits stated below for a variation of test frequency of 5%. 1.1 Using the least sensitive range, the i
28、ndication of frequency of between0.8Hz and20Hz should be linear up to full scale. NOTEIt may be desirable to have provision for overload conditions which are greater than the normal full-scale value. 1.2 Under steady-state conditions, the error of indication should not exceed 10% of the normal full-
29、scale value. This error should not exceed 15% for any of the conditions shown below. 1.2.1 Input voltage deviation of6dB during the measurement. 1.2.2 When a30% rectangular4Hz amplitude modulation is superimposed on an input signal which is arbitrarily frequency modulated so that the meter reads0.15
30、% in the absence of the amplitude modulation. 1.2.3 When frequencies of up to180Hz (for example, hum) are contributing up to20% r.m.s, of the total input voltage. 1.2.4 Line voltage deviations of 10%. 1.2.5 Room temperature variations of between15 C and35 C (after the equipment has been operating fo
31、r at least15min). 1.2.6 External50Hz (or60Hz) field of4A/m. 1.3 The required input voltage shall not exceed100mV. An indication of the correct level is desirable. 1.4 The input impedance should not be less than300k7 at3150Hz. 1.5 Provisions for connecting external filters or other analyzing equipmen
32、t, for example an oscillograph, are desirable. Approximately1V output should be provided for all full-scale readings. Appendix B Explanatory notes In sound recording, it is impossible to obtain completely constant speed of the recording medium because of the limited precision of the mechanical drive
33、. It is impossible to avoid short-term variations (flutter and wow) and there is also often a difference between the average speed at the beginning and at the end of the recording (drift). For a constant frequency f, the wavelength varies in recording proportionately to the transport speed v accordi
34、ng to the equation = v/f. When reproduced with a perfect drive (v=constant), the frequency which was so recorded will show a corresponding frequency modulation. In practice, however, the reproducing system adds its own speed variations, and the consequent frequency modulation adds vectorially to tha
35、t from the recording. The transport speed variations are best measured by recording a test frequency and then measuring the frequency variations in the subsequent reproduction. 1 Measuring short-time variations (flutter and wow) When no recording or reproducing machine is available with speed variat
36、ions much smaller than those of the machine under test, recording and reproduction is usually done on the machine under test. Therefore, a vectorial addition of the two identical variations occurs, and the resulting variations depend upon the phase relation between the two components. In extreme cas
37、es, the result is very nearly arithmetic addition. Since the ears sensitivity to frequency variations depends on the variation frequency, the measurements are performed with a weighting filter which approximates the characteristics of the ear. A satisfactory approximation is possible only at the rel
38、atively low variation frequencies. At frequencies above approximately100Hz, the disturbing effect depends mostly on the frequency and the level of the recorded tones. This disturbance can be significant under certain conditions. In order to obtain readings that are at least comparable, the weighting
39、 curve is defined up to200Hz. If, in special cases, large variations appear at higher frequencies (for example, the longitudinal tape vibrations), special measuring procedures are necessary. The fact that the frequency variations are normally non-sinusoidal makes it necessary also to specify the pro
40、perties of the rectifier circuit and the indicating instrument.BS4847:1989 6 BSI 12-1999 In some countries the r.m.s, value of the frequency variation is measured. Since different weighting curves, or none at all, are sometimes used in those countries, the results cannot be compared directly with th
41、ose obtained from the preceding method. 2 Measuring long-term deviations (drift) This measurement is of particular importance when a non-sychronous (e.g.,friction) drive is used, as for example with tapes without perforations. Tapes are often edited after recording, so that the location of a given s
42、ection of the tape within the tape spool is changed. When drift occurs, sections of tape which have been recorded with different speeds may be edited together. In this case, a sudden change in pitch will occur in reproduction, which can be especially disturbing in musical recording. In order to meas
43、ure the drift, a test tone may be recorded for say30s at the beginning of a full reel of tape of the maximum size which can be accommodated by the machine under test. The take-up reel containing the30s recording can then be transferred onto the supply turntable whilst the reel with the remainder of
44、the tape is transferred to the take-up turntable. If there is drift, reproduction under these conditions results in the frequency changing from the original recorded frequency. The relative frequency difference is called “drift”. In disk and film recording, test records and films of sufficient accur
45、acy are available, so that the drift can be measured directly. The frequency variations are normally measured by means of a frequency discriminator. If the coupling network following the discriminator does not pass d.c., this method cannot be used for drift measurement. In this case, the drift may b
46、e measured by counting the beats between the reproduced frequency and the frequency from the generator which was used in recording. When testing disk equipment, the frequency obtained from the inner grooves is compared with the frequency from a generator which has been adjusted to the frequency obta
47、ined from the outer grooves. One variation of this method of drift measurement which may be used with tape machines is to record the line frequency, and after exchange of tape spools, compare the reproduced frequency with the line frequency. This has the advantage in machines driven from the line th
48、at the errors due to variations of line frequency are cancelled out, provided that the line frequency has remained constant throughout the test. 3 Measuring the absolute speed When a non-slip drive is used, it is possible to measure the absolute speed of the medium by reproducing a recording of the
49、exact test frequency and comparing the reproduced frequency with a standard frequency of3150Hz. It does not seem reasonable to demand the necessary frequency accuracy and stability of the frequency variation (drift) meter itself. The exact measurement of the speed of a non-perforated tape is very difficult. The use of a test tape for such a speed measurement presents a problem beca
