1、 Recommendation ITU-R BS.2032(01/2013)Synchronization of digital audio sample clock to video referencesBS SeriesBroadcasting service (sound)ii Rec. ITU-R BS.2032 Foreword The role of the Radiocommunication Sector is to ensure the rational, equitable, efficient and economical use of the radio-frequen
2、cy spectrum by all radiocommunication services, including satellite services, and carry out studies without limit of frequency range on the basis of which Recommendations are adopted. The regulatory and policy functions of the Radiocommunication Sector are performed by World and Regional Radiocommun
3、ication Conferences and Radiocommunication Assemblies supported by Study Groups. Policy on Intellectual Property Right (IPR) ITU-R policy on IPR is described in the Common Patent Policy for ITU-T/ITU-R/ISO/IEC referenced in Annex 1 of Resolution ITU-R 1. Forms to be used for the submission of patent
4、 statements and licensing declarations by patent holders are available from http:/www.itu.int/ITU-R/go/patents/en where the Guidelines for Implementation of the Common Patent Policy for ITU-T/ITU-R/ISO/IEC and the ITU-R patent information database can also be found. Series of ITU-R Recommendations (
5、Also available online at http:/www.itu.int/publ/R-REC/en) Series Title BO Satellite delivery BR Recording for production, archival and play-out; film for television BS Broadcasting service (sound) BT Broadcasting service (television) F Fixed service M Mobile, radiodetermination, amateur and related
6、satellite services P Radiowave propagation RA Radio astronomy RS Remote sensing systems S Fixed-satellite service SA Space applications and meteorology SF Frequency sharing and coordination between fixed-satellite and fixed service systems SM Spectrum management SNG Satellite news gathering TF Time
7、signals and frequency standards emissions V Vocabulary and related subjects Note: This ITU-R Recommendation was approved in English under the procedure detailed in Resolution ITU-R 1. Electronic Publication Geneva, 2013 ITU 2013 All rights reserved. No part of this publication may be reproduced, by
8、any means whatsoever, without written permission of ITU. Rec. ITU-R BS.2032 1 RECOMMENDATION ITU-R BS.2032 Synchronization of digital audio sample clock to video references (2013) Scope This Recommendation provides methods for synchronizing interconnected digital audio equipment, and to address sync
9、hronization of the audio sample clocks to video reference signals. Synchronization of digital audio signals is a necessary function for the exchange of signals between equipment. The objective of synchronization is primarily to time align sample clocks within digital audio signal sources and align t
10、hem with video frames/fields. The provisions make use of the two-channel digital audio interface standard for professional use, Recommendation ITU-R BS.647. The ITU Radiocommunication Assembly, considering a) that digital audio implementations have been widely deployed; b) that there would be advant
11、ages if all digital audio equipment use the same synchronizing signal; c) that Recommendation ITU-R BS.647 requires the use of a video synchronizing signal; d) that a common synchronizing signal should be used for digital video and audio equipment; e) that for non-TV-video related applications, a re
12、ference signal is still required for multiple source applications, recommends 1 that synchronization of digital audio sample clock to video references defined in Annex 1 should be used; 2 that compliance with this Recommendation is voluntary. However, the Recommendation may contain certain mandatory
13、 provisions (to ensure, e.g. interoperability or applicability) and compliance with the Recommendation is achieved when all of these mandatory provisions are met. The words “shall” or some other obligatory language such as “must” and the negative equivalents are used to express requirements. 2 Rec.
14、ITU-R BS.2032 Annex 1 The primary area of application is the digital interconnection and synchronization of digital audio equipment contained within the production and acquisition environment. A further important objective is to define a means to synchronize digital audio sample clocks to a video re
15、ference signal. 1 Modes of operation 1.1 General Equipment should provide the ability to lock an internal sample-clock generator to a Digital Audio Reference Signal (DARS). 1.2 Synchronizing methods Equipment should be synchronized by one of three methods. NOTE In some circumstances, “word clock” ma
16、y be used in a manner similar to the DARS signal. Word clock is not part of this Recommendation, but is described in Appendix 2. 1.2.1 DARS referenced Equipment is synchronized to a DARS, which ensures that all input-output equipment sample clocks are locked to the same reference frequency and withi
17、n the phase tolerance specified in this Recommendation. In situations where some 96 kHz signals are carried in the mode described in Recommendation ITU-R BS.647 as “single channel double sampling frequency mode”, it is necessary that the synchronizing reference signal has a frequency component at 48
18、 kHz or lower, in order that two channels comprising a stereo pair shall be correctly related. Appendix 1 illustrates preferred phase relationships. 1.2.2 Video referenced A master video reference is used to derive a DARS, locking video and audio signals at the sample-rate level and to video frame b
19、oundaries. 1.2.3 GPS referenced A GPS receiver is used to reference a DARS, providing frequency and phase (from one-second pulses), and time-of-day sample address code in bytes 18 to 21 of channel status to support a time of day reference in locked equipment. 1.3 DARS distribution The DARS shall be
20、distributed in compliance with Recommendation ITU-R BS.647. 1.4 External signals 1.4.1 General When connecting external signals to an otherwise synchronous digital audio studio or production facility, 1.4.2 shall apply. Rec. ITU-R BS.2032 3 1.4.2 Phase correction Where the incoming signal is identic
21、al in sample frequency but is out of phase with the DARS, Recommendation ITU-R BS.647 frame alignment shall be applied. 1.5 Video referencing 1.5.1 General In the case of a combined video and audio environment, the source of the DARS shall be locked to the video source so that the mathematical relat
22、ionships given in Table 1 are obtained precisely. TABLE 1 Audio-video synchronization Sample rate (kHz) Samples per frame 25 Hz 30 Hz 29.97 Hz 50 Hz 60 Hz 59.94 Hz 48 1920 1600 8008/5 960 800 4004/5 96 3840 3200 16016/5 1920 1600 8008/5 1.5.2 Integer ratios For video systems with an integer number o
23、f Recommendation ITU-R BS.647 frames in one video frame, the Recommendation ITU-R BS.647 audio can be locked synchronously to the video. 1.5.3 Non-integer ratios 5-frame lock For video systems with fractions of Recommendation ITU-R BS.647 frames in one video frame, Recommendation ITU-R BS.647 audio
24、sample clocks can be locked using the video reference signal defined in Appendix 3. In this case, there is a 5-frame locking cycle. 1.5.4 Non-integer ratios Random lock It is common practice that the audio sample clock is synchronized on a video frame at random. While the frequency of the sample clo
25、ck will be locked, the absolute phasing will not be maintained. Systems that utilize this means of locking do require buffers to ensure phasing of all equipment. NOTE While every effort is taken to maintain a 5-frame sequence, it is not unusual for there to be less or greater number of samples withi
26、n the 5-frame sequence. These discrepancies occur when material is edited or switched. 2 Recommended practice for equipment synchronization 2.1 DARS requirements 2.1.1 DARS format The DARS shall have the format and electrical configuration of the two-channel digital audio interface and use the same
27、connector as given in Recommendation ITU-R BS.647. However, the basic structure of the digital audio interface format, where only the preamble is active, shall be acceptable as a digital audio synchronizing signal. 4 Rec. ITU-R BS.2032 2.1.2 DARS grade A DARS may be categorized as either grade 1 or
28、grade 2. See also 2.2. To be compliant with this Recommendation, only a grade 1 DARS signal is permitted. 2.1.2.1 Grade 1 A grade 1 DARS is a high-accuracy signal intended for synchronizing systematically a multiple-studio complex and may also be used for a stand-alone studio. 2.1.3 DARS identificat
29、ion A DARS, which has the prime purpose of studio synchronization, shall be identified as to its intended use by byte 4, bits 0 and 1, of Recommendation ITU-R BS.647 channel status: TABLE 2 Byte 4, bits 0 and 1: DARS Bits 1 0 Digital audio reference signal States 0 0 Not a reference signal (default)
30、 1 0 Grade 1 reference signal 0 1 Grade 2 reference signal* 1 1 Reserved and not to be used until further defined * Not used in this Recommendation. 2.1.4 DARS non-audio content A DARS shall be identified in channel status as “not linear PCM” when it contains other data rendering it unusable as a no
31、rmal audio signal. See Recommendation ITU-R BS.647, channel status. NOTE A DARS may carry an alignment tone in linear PCM form. 2.1.5 DARS date and time Where a DARS is used to carry date and time information in the user channel, this shall be signalled in channel status using the bits specified in
32、Recommendation ITU-R BS.6471for the carriage of metadata in the user channel. 2.1.6 DARS sampling frequency Sampling frequencies distributed by a DARS shall be 48 kHz or 96 kHz (see 2.2.2). 2.2 Sample frequency tolerances in equipment 2.2.1 Long-term frequency accuracy A grade 1 DARS signal shall ma
33、intain a long-term frequency accuracy within 1 part per million (ppm) relative to its rated frequency. Equipment designed to provide grade 1 reference signals shall only be required to lock to other grade 1 reference signals. 1Recommendation ITU-R BS.647-3 (2011), Part 3 3.3. Rec. ITU-R BS.2032 5 2.
34、2.2 Capture range The minimum capture range of equipment oscillators designed to lock to external inputs should be 2 ppm for grade 1 equipment. 2.3 Equipment timing relationships 2.3.1 General The timing-reference point is used to define the timing relationship between the DARS and digital audio inp
35、ut and output signals. 2.3.1.1 Output timing phase The difference between the timing-reference points of the DARS and all output signals, at the equipment connector points, shall be less than 5 % of the Recommendation ITU-R BS.647 frame period. The timing reference point of an output signal with dou
36、ble-rate or higher sampling frequency shall be within the stated tolerance at its own Recommendation ITU-R BS.647 frame rate. 2.3.1.2 Device delay Receivers shall be designed so that the number of samples of delay through a device remains constant and known while the difference between the timing-re
37、ference points of the DARS and all input signals is less than 25 % of the Recommendation ITU-R BS.647 frame period. 2.3.2 Timing limits Table 3 specifies tolerances values for the sample frequencies for use with this Recommendation. TABLE 3 Synchronization of digital audio: limits Professional sampl
38、ing frequency (kHz) Synchronization window s 1/fsPermitted variation, Input ( 2.3.1.2) Permitted variation, Output ( 2.3.1.1) 48 20.83 5.2 1.0 96 10.41 2.6 0.5 2.4 Video reference2One of the objectives of this Recommendation is to define the start of the X or Z preamble of the DARS to a known point
39、in the video reference signal. 2.4.1 25 or 50 Hz reference It is common practice in 25 or 50 Hz related TV systems to utilize a colour black analogue PAL signal. The PAL signal waveform is defined in Recommendation ITU-R BT.1700. 2For the purpose of this Recommendation, the interface line numbers ar
40、e used for the establishment of the timing references. 6 Rec. ITU-R BS.2032 2.4.1.1 Video interface format timing V and H sync phase relationship between 1125/50/I and 1125/25/P tri-level sync, and 625/50/I analogue sync is shown in Fig. 1. FIGURE 1 Line numbering of 1125/50/I, 1125/25/PsF, 1125/25/
41、P, and 625/50/I formats BS.2032-011125/50/I, 25/PsF Tri-level analog sync1122 1123 1124 1125 1 2 3 4 5 6 71125/25/P Tri-level analog sync11241122 1123 1125 1 2 3 4 5 6 7625/50/I Analog sync624 625 1 2 3 4FIGURE 2 DARS X preamble reference BS.2032-02Video referencesignalHalf amplitudepointDARSX Pream
42、bleLine 1625/50/I 1125/50/IThe DARS X Preamble shall be referenced to the half-amplitude point of the leading edge of the synchronization pulse of line 1 of the television signal on every video frame. Rec. ITU-R BS.2032 7 2.4.2 30 or 603Hz reference V and H sync phase relationship between 1125/59.94
43、/I and 1125/29.97/P tri-level sync, and 525/60/I analogue sync is shown in Fig. 3. 2.4.2.1 Video interface format timing FIGURE 3 Line numbering of 1125/59.94/I, 1125/29.97/PsF, 1125/29.97/P and 525/59.94/I BS.2032-031125/59.94/I and 29.97/PsF Tri-level analog sync1122 1123 1124 1125 1 2 3 4 5 6 711
44、25/29.97/P Tri-level analog sync1122 1123 1124 1125 5 6 712525/59.94/I Analog sync3456234FIGURE 4 DARS X preamble reference BS.2032-04Video referencesignalHalf amplitudepointDARSX preambleDrawing not to scaleLine 1 1125/59.94/ILine 4 525/59.94/I3Precise values are 30/1.001 and 60/1.001. 8 Rec. ITU-R
45、 BS.2032 The DARS X Preamble shall be referenced to the half-amplitude point of the leading edge of the synchronization pulse of line 1 for 1080 systems and line 4 for 525 line systems. Alignment of the DARS X preamble should be timed for every 5thframe. There is a possibility that there could be a
46、1 sample offset. The 525 line reference signal with 5 frame identification is shown in Appendix 3. 2.4.3 Overall phase tolerance To aid practical implementations, there shall be a phase tolerance of 5% of the Recommendation ITU-R BS.647 frame period between the DARS signals and the video reference,
47、in addition to the 5% tolerance defined for digital audio synchronization at the system outputs in 2.3.1.1. 2.5 System practice Good engineering practice requires that timing differences between signal paths be minimized, to avoid timing errors accumulating with a risk of loss of synchronism. 2.6 Cl
48、ock jitter Jitter noise may be either random or in the form of modulation, which at frequencies less than sample rate will cause a timing error to accumulate according to the amplitude and frequency of the modulation waveform. NOTE Recommendation ITU-R BS.647 defines limits for jitter on the digital
49、 audio interface. 3 Date and time Flagging of date and time in channel status is specified in 2.1.5. This may take a convenient form for transfer to Recommendation ITU-R BS.647 metadata stream. Rec. ITU-R BS.2032 9 Appendix 1 (Informative) Timing relationships FIGURE 5 Preferred phase relationships and channel usage BS.2032-05XYXYDARSAAVideo referenceWorld clockChannel Asample nChannel Bsample nChannel Asample 1n+Channel Bsample 1n+Channel Asample nChannel Asample 1n+Channel Asample 2n+Channel Asample 3n+BS 647-3 48 kHz2 channelBS 647-3 96 kHz single
