1、BRITISH STANDARD BS7486-1: 1991 IEC1053-1: 1991 Specification for Helical-scan video tape cassette system using12,65mm(0,5in) magnetic tape on type beta format FM audio recording Part 1: 625 line-50 field systemsBS7486-1:1991 This BritishStandard, having been prepared under the directionof the Elect
2、ronic Equipment Standards Policy Committee, was published underthe authority of the Standards Board and comes intoeffect on 30September1991 BSI01-2000 The following BSI references relate to the work on this standard: Committee reference EEL/22 Draft for comment 88/30303 DC ISBN 0 580 20028 0 Committ
3、ees 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: Association of Professional Recording Services Ltd. Audio Eng
4、ineering Society British Broadcasting Corporation British Kinematograph, Sound and Television Society British Tape Industry Association Independent Television Association Independent Television Commission National Council for Educational Technology (NCET) Royal Photographic Society Royal Television
5、Society Sound and Communication Industries Federation Amendments issued since publication Amd. No. Date CommentsBS7486-1:1991 BSI 01-2000 i Contents Page Committees responsible Inside front cover National foreword ii 1 Scope 1 2 Normative reference 1 3 Recording method 1 4 Mechanical configuration 1
6、 4.1 FM audio track pattern 1 4.2 Head azimuth angles 1 4.3 Recording time difference 1 5 Recording characteristics 1 5.1 Dynamic emphasis 1 5.2 Carrier centre frequency 1 5.3 Frequency deviation 1 5.4 Recording level 2 5.5 Modulation polarity 2 6 Other subjects 2 6.1 Channel application 2 Annex A (
7、normative) Encoder transient measurement method 6 Figure 1 Track pattern of beta for FM audio system (625 lines-50 field) 3 Figure 2 Video and FM audio signal spectrum (625 line-50 field) 4 Figure 3 Block diagram of FM audio recording system 5 Figure 4 Block diagram of dynamic emphasis 5 Table 1 Hea
8、d azimuth angles 1 Table 2 Frequency response Encode mode 2 Table 3 Channel application 2 Publication(s) referred to Inside back coverBS7486-1:1991 ii BSI 01-2000 National foreword This Part of BS7486 has been prepared under the direction of the Electronic Equipment Standards Policy Committee and is
9、 identical with IEC1053-1:1991 “Helical-scan video tape cassette system using12,65mm (0,5in) magnetic tape on type beta format FM audio recording Part1:625 line-50 field systems”, published by the International Electrotechnical Commission (IEC). A British Standard does not purport to include all the
10、 necessary provisions of a contract. Users of British Standards are responsible for their correct application. Compliance with a British Standard does not of itself confer immunity from legal obligations. Cross-reference International Standard Corresponding BritishStandard IEC767:1983 BS6502:1984 Sp
11、ecification for helical-scan video tape cassette system using12.65mm (0.5in) magnetic tape on type Beta format (Identical) Summary of pages This document comprises a front cover, an inside front cover, pagesi andii, pages1 to6, an inside back cover and a back cover. This standard has been updated (s
12、ee copyright date) and may have had amendments incorporated. This will be indicated in the amendment table on the inside front cover.BS7486-1:1991 BSI 01-2000 1 1 Scope This part of IEC1053 is applicable to frequency modulation (FM) audio recording on video recorders fully compatible with the beta f
13、ormat for625 lines-50 field television systems defined in IEC767. The object of this part is to define the electrical and mechanical characteristics of FM audio recording which will provide for the interchangeability of recorded cassettes. The requirements given relate to625 lines-50 field systems.
14、2 Normative reference The following standard contains provisions which, through reference in this text, constitute provisions of this part of IEC1053. At the time of publication of this standard, the editions indicated were valid. All standards are subject to revision, and parties to agreements base
15、d on this part of IEC1053 are encouraged to investigate the possibility of applying the most recent edition of the standard indicated below. Members of IEC and ISO maintain registers of currently valid International Standards. IEC767:1983, Helical-scan video tape cassette system using12,65mm (0,5in)
16、 magnetic tape on type beta format. 3 Recording method The method of recording the audio signal using frequency modulation is specified. The audio signal is recorded in the deep layer of the magnetic tape in the video track area prior to the video recording, with additional audio heads mounted on th
17、e common video rotating drum. The video signal is recorded on the surface layer according to IEC767 (Depth-Multiplex recording system). The audio and video heads have different inclined azimuth gap angles to prevent mutual influences between audio and video signals. 4 Mechanical configuration 4.1 FM
18、 audio track pattern The centre of the FM audio tracks is shifted from the centre of the video track as shown in Figure 1. The dimensions shall be as follows: 4.2 Head azimuth angles The head azimuth angles shall be in accordance with Table 1 below. Table 1 Head azimuth angles 4.3 Recording time dif
19、ference The FM audio heads shall be arranged so that the FM audio signal will be recorded within a time difference of 10ms between the point V of the video track and the point A of the FM audio track (seeFigure 1). 5 Recording characteristics The two channels of audio signal are recorded as FM signa
20、ls with different carrier frequencies. The recording signal spectrum is shown in Figure 2. A block diagram of this system is shown in Figure 3. 5.1 Dynamic emphasis Dynamic emphasis shall be applied during FM audio recording as shown in Figure 4. The characteristics shall be as in Table 2. Transient
21、: 5.2 Carrier centre frequency The carrier centre frequency shall be as follows: 5.3 Frequency deviation The frequency deviation shall be as follows: S: FM audio video track offset 54,34m 64m A1 A2 FM audio track width max.16,44m min.14.04m Track A Track B Track a Track b FM audio head azimuth angle
22、 30 30 30 30 Video head azimuth angle a (+7 ) a (7 ) (SeeFigure 1) a The values are from IEC767. attack time: 1,5ms recovery time: 36ms hold time: 16ms (tolerance 20%) (seeAnnex A). NOTEDynamic emphasis means noise reduction combined with FM pre-emphasis. CH-L (left channel) f 1 =1,44MHz 20kHz CH-R
23、(right channel) f 2 =2,10MHz 20kHz Maximum frequency deviation: 200kHz Operating frequency deviation: 66,7kHz at400kHz (Frequency deviation at the reference level)BS7486-1:1991 2 BSI 01-2000 Table 2 Frequency response Encode mode 5.4 Recording level The FM audio signal shall be recorded so that the
24、playback levels of left and right channels shall be approximately equal and maximum after the video signal is recorded. 5.5 Modulation polarity The modulation polarity of CH-L and CH-R audio signals shall be the same. 6 Other subjects 6.1 Channel application In the case of stereo recording, the chan
25、nel application of FM audio signals shall be as shown in Table 3 below. Table 3 Channel application Input level (dB) Frequency 50Hz 100Hz 200Hz 400Hz 700Hz 1kHz 2kHz 4kHz 7kHz 10kHz 15kHz 0 +2,7 +0,9 0 0 +0,4 +0,6 +0,9 +2,2 +3,7 10 3,2 5,1 6,1 6,2 6,0 5,8 5,3 3,9 2,0 0,5 20 8,9 10,8 11,8 12,1 11,9 1
26、1,6 11,0 9,4 7,6 6,1 4,9 30 14,4 16,3 17,5 17,8 17,6 17,2 16,5 14,6 12,8 11,5 10,3 40 20,1 21,9 22,9 23,2 23,0 22,7 21,7 19,9 18.1 16,8 15,6 Tolerance 2dB 0dB of the encode level is the maximum frequency deviation level. Monaural recording Main-sub recording CH-L a Monaural signal Main signal CH-R a
27、 Monaural signal Sub signal a Both CH-L and CH-R carriers shall be recorded.BS 7486-1:1991 BSI 01-2000 3 NOTEThe offset S on the tape pattern is the distance from the centre line of the video track to the centre line of the FM audio track. Figure 1 Track pattern of beta for FM audio system (625 line
28、s-50 field)BS7486-1:1991 4 BSI 01-2000 Figure 2 Video and FM audio signal spectrum (625 line-50 field)BS7486-1:1991 BSI 01-2000 5 Figure 3 Block diagram of FM audio recording system Figure 4 Block diagram of dynamic emphasisBS7486-1:1991 6 BSI 01-2000 Annex A (normative) Encoder transient measuremen
29、t method Source signal: 5 kHz tone burst. Encoder outputBS7486-1:1991 BSI 01-2000 Publication(s) referred to Seenational foreword.BS7486-1: 1991 IEC1053-1: 1991 BSI 389 Chiswick High Road London W4 4AL BSIBritishStandardsInstitution BSI is the independent national body responsible for preparing Brit
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