1、BRITISH STANDARD BS EN 60756:1993 IEC756:1991 Incorporating Amendment No.1 Non-broadcast video tape recorders Time base stability The European Standard EN60756:1993 has the status of a BritishStandard UDC 621.397.037.732BSEN60756:1993 This BritishStandard, having been prepared under the directionof
2、the Electronic Equipment Standards Policy Committee, was published underthe authority of the Standards Board and comesintoeffect on 30 September1991 BSI04-2000 First published September1983 Second edition September1991 The following BSI references relate to the work on this standard: Committee refer
3、ence EEL/22 Draft for comment88/32268DC ISBN 0 580 20026 4 Committees 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 represen
4、ted: Association of Professional Recording Services Ltd. Audio Engineering Society British Broadcasting Corporation British Kinematograph, Sound and Television Society British Tape Industry Association Independent Television Association Independent Television Commission National Council for Educatio
5、nal Technology (NCET) Royal Photographic Society Royal Television Society Sound and Communication Industries Federation Amendments issued since publication Amd. No. Date Comments 7736 April1993 Indicated by a sideline in the marginBSEN60756:1993 BSI 04-2000 i Contents Page Committees responsible Ins
6、ide front cover National foreword ii Foreword 2 Text of EN 60756 3BSEN60756:1993 ii BSI 04-2000 National foreword This BritishStandard has been prepared under the direction of the Electronic Equipment Standards Policy Committee and is identical with IEC756:1991 “Non-broadcast video tape recorders Ti
7、me base stability”, published by the International Electrotechnical Commission (IEC). This BritishStandard supersedes BS6411:1983 which is withdrawn. In1993 the European Committee for Electrotechnical Standardization (CENELEC) accepted IEC756:1991 as European Standard EN60756:1992. As a consequence
8、of implementing the European Standard this BritishStandard is renumbered as BS EN60756 and any reference to BS6411 should be read as a reference to BS EN60756. A British Standard does not purport to include all the necessary provisions of a contract. Users of British Standards are responsible for th
9、eir 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, theEN title page, pages2 to8 and a back cover. This standard has been updated (see copyr
10、ight date) and may have had amendments incorporated. This will be indicated in the amendment table on the inside front cover.EUROPEAN STANDARD NORME EUROPENNE EUROPISCHE NORM EN60756 January1993 UDC 621.397.037.732 Descriptors: Stability, time base, magnetic videorecording English version Non-broadc
11、ast video tape recorders Time base stability (IEC756:1991) Magntoscopes utiliss hors de la radiodiffusion Stabilit de base de temps (CEI756:1991) Videobandgerte fr den Gebrauch auerhalb des Rundfunks Zeitbasisstabilitt (IEC756:1991) This European Standard was approved by CENELEC on1992-12-09. CENELE
12、C members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this European Standard the status of a national standard without any alteration. Up-to-date lists and bibliographical references concerning such national standards may be obtained on app
13、lication to the Central Secretariat or to any CENELEC member. This European Standard exists in three official versions (English, French, German). A version in any other language made by translation under the responsibility of a CENELEC member into its own language and notified to the Central Secreta
14、riat has the same status as the official versions. CENELEC members are the national electrotechnical committees of Austria, Belgium, Denmark, Finland, France, Germany, Greece, Iceland, Ireland, Italy, Luxembourg, Netherlands, Norway, Portugal, Spain, Sweden, Switzerland andUnitedKingdom. CENELEC Eur
15、opean Committee for Electrotechnical Standardization Comit Europen de Normalisation Electrotechnique Europisches Komitee fr Elektrotechnische Normung Central Secretariat: rue de Stassart 35, B-1050 Brussels 1993 Copyright reserved to CENELEC members Ref. No. EN60756:1993 EEN60756:1993 BSI 04-2000 2
16、Foreword The CENELEC questionnaire procedure, performed for finding out whether or not the International Standard IEC756:1991 could be accepted without textual changes, has shown that no common modifications were necessary for the acceptance as European Standard. The reference document was submitted
17、 to the CENELEC members for formal vote and was approved by CENELEC as EN60756 on9 December1992. This European Standard supersedes HD458 S1:1985. The following dates were fixed: Contents Page Foreword 2 1 Scope and object 3 2 Definitions concerning time base stability 3 2.1 Gap 3 2.2 Phase step 3 2.
18、3 Deviation of line frequency 3 2.4 Deviation of colour carrier frequency 3 2.5 Relative displacement 3 3 Measurement of time base errors 3 3.1 Gap 3 3.2 Phase step 4 3.3 Deviation of line frequency 4 3.4 Deviation of colour carrier frequency 4 4 Maximum values of time base errors 4 4.1 Gap 4 4.2 Ph
19、ase step 4 4.3 Deviation of line frequency 4 4.4 Deviation of colour carrier frequency 5 5 Weighting curves 5 5.1 Weighting curve for CCIR System525/60 5 5.2 Weighting curve for CCIR System625/50 5 6 Time base stability at playback speeds different from the nominal value 5 6.1 Signal transitions 6 6
20、.2 Horizontal synchronizing signal 6 6.3 Vertical synchronizing signal 7 Figure 1 Signal transition (one field) One head is used per scan 7 Figure 2 Signal transitions (one field) More than one head is used per scan 8 Figure 3 Test arrangement for checking the distortion of the synchronizing signal
21、due to signal transitions during playback in “trick”-mode 8 latest date of publication of an identical national standard (dop)1993-12-01 latest date of withdrawal of conflicting national standards (dow)1993-12-01EN60756:1993 BSI 04-2000 3 1 Scope and object This International Standard specifies the
22、time base errors of the monochrome as well as of the colour composite video signal reproduced from two head helical-scan domestic video recorders, recording one field on each track. This standard gives characteristics and maximum figures of the time base errors to make it possible to design the hori
23、zontal flywheel of television receivers so as to ensure acceptable stability on the screen. 2 Definitions concerning time base stability 2.1 gap loss of video signal during a certain period of each field 2.2 Phase step 2.2.1 due to a difference between the length of the head path and the length of t
24、he recorded track, a phase step occurs at the end of the gap respectively at the time of switching from one track to the next. The sign of the phase step depends on the sign of the difference of lengths 2.2.2 due to a deviation of the angle between the two video heads from the theoretical value of18
25、0 , a phase step occurs at the end of the gap respectively at the time of switching from one track to the next. The sign of the phase step alternates from one field to the next 2.3 Deviation of line frequency 2.3.1 the mean value of the line frequency is determined by the source to which the recorde
26、r is locked. If the frequency of this source deviates from the frequency of the source used during recording, the mean value of the line frequency of the playback signal will differ from its original value. If the machine is not locked to an external reference, the deviation will depend on the diffe
27、rence between head speed during recording and that during playback 2.3.2 because neither head nor tape velocities are constant, a jitter of the line frequency occurs containing various frequency components which depend on mechanical parts of the tape deck and varying tape properties 2.4 Deviation of
28、 colour carrier frequency 2.4.1 depending on the modulation system used in the colour signal processing, a deviation of the mean value of the colour carrier frequency from its original value may occur 2.4.2 depending on the modulation system used in the colour signal processing the jitter of the col
29、our carrier frequency will be a certain percentage of the jitter of the line frequency 2.5 relative displacement relative displacement is defined as the ratio of the horizontal displacement of a picture element to the line interval 3 Measurement of time base errors 3.1 Gap The timing of the gap rela
30、tive to the vertical sync pulse, the gap duration and signals during the gap shall be measured with an oscilloscope.EN60756:1993 4 BSI 04-2000 3.2 Phase step The phase step due to a difference of lengths and the phase step due to a deviation of angles are superimposed and shall be measured on the sc
31、reen of a monitor or of a television set. This shall be done by measuring the horizontal deviation of a vertical bar at the end of the gap with respect to the horizontal position of the vertical bar at the beginning of the gap respectively before and after the time of switching from one track to the
32、 next. 3.3 Deviation of line frequency 3.3.1 The mean value of the line frequency shall be measured by a counter or a frequency discriminator having a long time constant with respect to the line frequency. 3.3.2 The jitter of the line frequency shall be measured by a frequency discriminator or by me
33、asuring the line period. The jitter shall be determined by the percentage of peak-to-peak deviation from the average value %f H(pp) /f Hand weighted by a weighting curve due to the fact that the reaction of the horizontal flywheel of television receivers depends on the frequency of the jitter. 3.4 D
34、eviation of colour carrier frequency 3.4.1 The mean value of the colour carrier frequency shall be measured by a frequency counter. 3.4.2 The method of measuring the jitter of the colour carrier frequency is under consideration. 4 Maximum values of time base errors 4.1 Gap The centre of the gap shou
35、ld lie three to15 lines before the leading edge of the vertical sync pulse. Theduration of the gap should be less than five lines. The signal during the gap shall be a constant level between black level and white level upon which an unwanted signal (e.g.noise) may be superimposed. Thepeak-to-peak am
36、plitude of the unwanted signal shall be less than60% of the sync amplitude. For machines with switched video heads, the following specifications shall apply: a) no signal gap shall occur; b) the switching position shall be five to ten lines before the start of vertical sync. If no disturbance in the
37、 sync occurs during switching, this figure may be0 to ten lines; c) the overlap duration shall be two lines minimum, including the switching point. 4.2 Phase step The total phase step shall not exceed: The phase error shall not exceed14s in both cases. NOTE 1Phase step is defined in2.2.1. NOTE 2Phas
38、e error is defined in2.2.2. 4.3 Deviation of line frequency 4.3.1 Deviation of the mean value of line frequency from its nominal value shall be less than: 4.3.2 Peak-to-peak deviation of line frequency shall be less than: The percentage of peak-to-peak deviation of the line frequency from its averag
39、e value (jitter) is weighted by the weighting curves shown in clause5. 6 4s for525 line/60Hz systems; 154s for625 line/50Hz systems. 4% for monochrome recorders; 0,5% for colour recorders for625 line/50Hz systems; 0,5% for525 line/60Hz systems. 0,3% for525 line/60Hz systems; 0,2% for625 line/50Hz sy
40、stems.EN60756:1993 BSI 04-2000 5 4.4 Deviation of colour carrier frequency 4.4.1 The deviation of the colour carrier frequency shall not exceed: 4.4.2 The limits for the jitter of the colour carrier frequency are under consideration. 5 Weighting curves The weighting curve represents the response of
41、the flywheel circuit of the TV receiver to jitter and shows at each frequency the relative displacement with respect to the jitter of the playback signal. Therefore, the movement on the screen corresponds to the jitter of the line frequency of the playback signal weighted by the weighting curve. 5.1
42、 Weighting curve for CCIR System525/60 The weighting curve is based on a horizontal flywheel of the television receiver having a minimum gain of16000, a resonant frequency of160Hz and a damping factor1,6. 5.2 Weighting curve for CCIR System625/50 The weighting curve is based on a horizontal flywheel
43、 of the television receiver having a minimum gain of30000, a resonant frequency of160Hz and a damping factor of2. This flywheel produces a maximum overshoot of20 lines after a phase step. There is only one overshoot having an amplitude of5% of the value of the phase step. This design ensures that a
44、phase step occurring before the vertical sync pulse will cause negligible “flagging” at the top of the picture. 6 Time base stability at playback speeds different from the nominal value Playback modes using tape speeds other than nominal are known as “trick”-modes. Examples are stop motion, fast mot
45、ion (picture search) or slow motion in both forward and reverse directions. 50Hz for the NTSC system; 150Hz for the PAL system; 1 kHz for the SECAM system.EN60756:1993 6 BSI 04-2000 These modes affect the time base of the playback signal and cause deviations from the values specified in clause4. 6.1
46、 Signal transitions 6.1.1 Signal transitions due to head switching at the end of a scan (indicated by S in Figure 1 and Figure 2). This signal transition is described in2.1, 3.1 and4.1. 6.1.2 Signal transitions due to “trick”-modes (indicated by T in Figure 1 and Figure 2). The following cases are d
47、istinguished: a) if one head is used per scan (seeFigure 1); b) if more than one head is used per scan (seeFigure 2); c) if special arrangements are used (e.g.actuators). 6.1.2.1 Number of signal transitions The maximum number of signal transitions per field depends on the ratio of the tape speed us
48、ed during “trick”-mode to the nominal tape speed, but the mean line frequency shall not exceed the limit indicated in6.2.1. 6.1.2.2 Position of signal transitions The position of the signal transitions with respect to the vertical synchronizing pulse is not defined and may vary as a function of time
49、. In successive fields the position is not necessarily the same. 6.1.2.3 Distortion of the synchronizing signal Depending on the characteristics of the disturbances of the sync signal the television receiver or monitor could detect an unwanted vertical synchronizing pulse producing a vertical instability of the picture. It is, therefore, necessary to check the playback signal by means of a test circuit. The test circuit shall consist of a sync separator followed by an integrating network having a time constant of154s. The outpu
