1、 Recommendation ITU-R BS.647-3(03/2011)A digital audio interfacefor broadcasting studiosBS SeriesBroadcasting service (sound)ii Rec. ITU-R BS.647-3 Foreword The role of the Radiocommunication Sector is to ensure the rational, equitable, efficient and economical use of the radio-frequency spectrum by
2、 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 Radiocommunication Confer
3、ences 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 statements an
4、d 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 (Also available
5、 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 satellite serv
6、ices 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 signals and fr
7、equency 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, 2011 ITU 2011 All rights reserved. No part of this publication may be reproduced, by any means what
8、soever, without written permission of ITU. Rec. ITU-R BS.647-3 1 RECOMMENDATION ITU-R BS.647-3*A digital audio interface for broadcasting studios (1986-1990-1992-2011) Scope This Recommendation specifies an interface for the serial digital transmission of two channels of periodically sampled and lin
9、early represented digital audio data to be used in broadcasting studios. The ITU Radiocommunication Assembly, considering a) that there is a need in broadcasting studios to interconnect in the digital domain various pieces of digital sound equipment; b) that there would be advantages if all equipmen
10、t used the same interface connections; c) that Recommendation ITU-R BS.646 Source encoding for digital sound signals in broadcasting studios, defines the digital sound format used for sound and television broadcasting applications; d) that the interface should make allowance for processing headroom;
11、 e) that the interface should allow for auxiliary data of various kinds to be carried, recommends 1 that the interface described in Annex 1 should be used for serial digital transmission of two channels of periodically sampled and linearly represented digital audio data in broadcasting studios. This
12、 same interface may be used as a transport of compressed audio signals and other user defined data; 2 that compliance with this Recommendation is voluntary. However, the Recommendation may contain certain mandatory provisions (to ensure e.g. interoperability or applicability) and compliance with the
13、 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. The use of such words shall in no way be construed to imply partial or total compliance with t
14、his Recommendation. *This Recommendation should be brought to the attention of the IEC and the Audio Engineering Society (AES). 2 Rec. ITU-R BS.647-3 Annex 1 Serial transmission format for two-channel linearly-represented digital audio data The following five parts (Part 1 to Part 5) specify an inte
15、rface for the serial digital transmission of two channels of periodically sampled and linearly represented digital audio data in broadcasting studios. Part 1 defines the terms applied for this specification. Part 2 defines the format for coding audio used for the audio content. Part 3 defines the fo
16、rmat for coding metadata, or subcode, relating to the audio content and carried with it. Part 4 defines the format for transport of a digital audio interface. Part 5 specifies the physical and electrical parameters for different media. Although this transmission specification is independent of sampl
17、ing frequency the interface is primarily intended to be used at 48 kHz as this is the recommended sampling frequency for use in broadcasting applications (Recommendation ITU-R BS.646).The Annex does not cover connection to any common carrier equipment. NOTE 1 In this interface specification, mention
18、 is made of an interface for consumer use. The two interfaces are not identical. TABLE OF CONTENTS Page Part 1 Terminology . 3 Part 2 Audio content . 5 Part 3 Metadata and subcode 7 Appendix A to Part 3 (Informative) Provision of additional, voice-quality channels . 17 Appendix B to Part 3 (Informat
19、ive) Generation of CRCC (byte 23) for channel status 18 Part 4 Transport . 19 Part 5 Physical and electrical parameters 24 Appendix A to Part 5 (Informative) Symbol rates and UI . 27 Appendix B to Part 5 (Informative) Balanced transmission 28 Appendix C to Part 5 (Normative) Coaxial transmission 32
20、Rec. ITU-R BS.647-3 3 Part 1 Terminology 1 Introduction This Part 1 defines the terms applied for this Recommendation. 2 Terminology For the purpose of this Recommendation the following definitions of terms apply. 2.1 Sampling frequency The frequency of the samples representing an audio signal. 2.2
21、Audio sample word A series of binary digits representing the amplitude of an audio sample, also known as a PCM sample. 2.3 Auxiliary sample bits The four least-significant bits (LSBs) of those allocated to audio which can be assigned as auxiliary sample bits and used for auxiliary information when t
22、he number of audio sample bits is less than or equal to 20. 2.4 Validity bit A bit indicating whether the audio sample bits in the same subframe are suitable for direct conversion to an analogue audio signal. 2.5 Most-significant bit In the context of this standard: the Most-significant bit (MSB) of
23、 an audio sample word, being the sign bit in the case of twos complement code. 2.6 Least-significant bit In the context of this standard: the Least-significant bit (LSB) of an audio sample word. 2.7 Subframe The smallest structural element in a transport defined in Part 4, carrying one PCM sample an
24、d ancillary information. 2.8 Channel status Bits carrying, in a fixed format derived from the block information associated with each audio channel which is decodable by any interface user. 2.9 User data Channel provided to carry any other information. 4 Rec. ITU-R BS.647-3 2.10 Metadata Information
25、relating to the audio content in the same channel. 2.11 Frame Sequence of two successive and associated subframes. 2.12 Biphase-mark Channel-coding (or line-coding) technique which minimizes DC content and maximizes clock-recovery energy relative to the original binary bitstream. 2.13 Even parity bi
26、t A bit whose value is chosen such that the total number of ones in the field which includes it is even. 2.14 Preambles Specific unique patterns used for synchronization, compatible with but not part of the biphase mark code. See 6 of Part 4. 2.15 Block Group of 192 consecutive frames with a defined
27、 start point. See 6 of Part 4. NOTE 1 The start of a block is designated by a special subframe preamble. See 5 and 6 of Part 4. 2.16 Channel coding/line coding Coding describing the method by which the binary digits are represented for transmission through the interface, see biphase mark above. 2.17
28、 Unit interval (UI) Shortest nominal time interval in the coding scheme. NOTE 1 There are 128 UI in a sample frame. See Appendix A to Part 5. 2.18 Interface jitter Deviation in timing of interface data transitions (zero crossings) when measured with respect to an ideal clock. 2.19 Intrinsic jitter O
29、utput interface jitter of a device that is either free-running or synchronized to a jitter-free reference. 2.20 Jitter gain Ratio, expressed in decibels, of the amplitude of jitter at the synchronization input of a device to the resultant jitter at the output of the device. NOTE 1 This definition ex
30、cludes the effect of intrinsic jitter. 2.21 Frame rate Frequency at which frames are transmitted. Rec. ITU-R BS.647-3 5 Part 2 Audio content 1 Introduction This Part 2 defines the format for coding audio used for the audio content. 2 Audio content 2.1 Audio content coding The audio content shall be
31、coded as linear PCM using 2s complement code. 2.2 PCM polarity Positive analogue voltages shall be represented by positive binary numbers. 2.3 Coding precision options The accuracy of the coding shall be between 16 and 24 bits, in two ranges for the purpose of indicating which length is in use in ch
32、annel status data, 16 to 20 bits and 20 to 24 bits. See Part 3. 2.4 Intermediate coding precision The interface permits maximum word lengths of either 20 or 24 bits. A source which provides fewer bits than this shall be justified to the MSB of the available word length and the unused LSBs shall be s
33、et to logic 0. NOTE 1 If a low-resolution signal were not so justified, then sign extension would be needed. 2.5 Non-audio content The interface may alternatively carry data or audio which is compressed or in a different format in place of linear PCM audio, in either channel B or both channels. In s
34、uch cases the validity bit shall be set independently in each channel and channel status encoded to indicate this. See Part 3. NOTE 1 Such use is not standardized here: provision is only made to protect standard equipment from such use. 2.6 DC content The coded audio shall contain as little equivale
35、nt DC offset as possible, and in any case less than the analogue equivalent noise level. 3 Sampling frequency 3.1 Channel interdependency The sampling frequency shall be the same in both channels. 6 Rec. ITU-R BS.647-3 3.2 Choice of sampling frequency The recommended sampling frequency for use in br
36、oadcasting applications is 48 kHz as per Recommendation ITU-R BS.646. 4 Validity bit 4.1 Channel validity usage The validity bit shall be set to logic 0 if the associated audio sample word is suitable for direct conversion to an analogue audio signal, and shall be set to logic 1 if it is not suitabl
37、e. Where channel status indicates (in byte 0 bit 1 (see Part 3) that the audio sample word is not in linear PCM form the validity bit shall be set to logic 1 in every subframe. There is no default state for the validity bit. 4.2 Independent channel validity Validity shall be set or reset for each an
38、d every sample independently in each channel. 5 Pre-emphasis 5.1 Pre-emphasis indication The use of pre-emphasis, 50 s pre-emphasis as per Recommendations ITU-R BS.450-3 or ITU-T J.17 pre-emphasis as per ITU-T Recommendation J.17, shall be indicated in channel status as defined in Part 3. Where no p
39、re-emphasis is used, this may be indicated. NOTE 1 Positive indication is strongly preferred. The default value will normally be taken to indicate no pre-emphasis, but this condition is undefined. Rec. ITU-R BS.647-3 7 Part 3 Metadata and subcode 1 Introduction This Part 3 defines the format for cod
40、ing metadata, or subcode, relating to the audio content and carried with it. 2 User data format One bit of user data may be carried in each subframe. Different user data may be carried in each channel and may or may not be related to the associated. Its capacity in kbit/s is therefore equal to the s
41、ampling frequency in use, in kilosamples/s, for each channel. User data bits may be used in any way desired by the user. Known possible formats for the user data channel are indicated by the channel status byte 1, bits 4 to 7. The default value of the user data bit is logic 0. 3 Channel status forma
42、t 3.1 Channel status bit One bit of channel status data shall be carried in each subframe. Different channel status data may be carried in each channel. Its capacity in kbit/s is therefore equal to the sampling frequency in use, in kilosamples/s. NOTE 1 The channel status for each audio signal carri
43、es information associated with that audio signal, and thus it is possible for different channel status data to be carried in the two subframes of the digital audio signal. Examples of information to be carried in the channel status are: length of audio sample words, number of audio channels, samplin
44、g frequency, sample address code, alphanumeric source and destination codes, and emphasis. 3.2 Channel status block Channel status information shall be organized in 192 bit blocks, subdivided into 8 bit bytes numbered from 0 to 23. The transmission format shall mark every 192nd frame to show that it
45、 carries the first bit of a block. Within each byte, the bits are numbered from 0 to 7, 0 being the first bit transmitted, so bit 0 of byte 0 is the first bit in the block. Where a byte holds a numerical value, bit 0 is the least-significant bit. NOTE 1 In Part 4, the frame that begins with preamble
46、 Z contains the first bit of a block in both channels. In other transports a “block start” flag is used to mark the first subframe in a block, and may be applied to each channel independently. 3.3 Channel status content The specific organization follows. Multiple-bit quantities are shown in the tabl
47、es with the most-significant bit to the left; note that the order in which the bits are transmitted is therefore from right to left. 8 Rec. ITU-R BS.647-3 FIGURE 1 Channel status data format Rec. ITU-R BS.647-3 9 3.3.1 Byte 0: Basic audio parameters Bit 0 Use of channel status block State 0 Consumer
48、 use of channel status block (see Note 1) 1 Professional use of channel status block Bit 1 Linear PCM identification State 0 Audio sample word represents linear PCM samples 1 Audio sample word used for purposes other than linear PCM samples Bits 4 3 2 Audio signal emphasis States 0 0 0 Emphasis not
49、indicated. Receiver defaults to no emphasis with manual override enabled 0 0 1 No emphasis. Receiver manual override is disabled 0 1 1 50 s + 15 s emphasis, see Recommendation ITU-R BS.450. Receiver manual override is disabled 1 1 1 ITU-T Recommendation J.17 emphasis (with 6.5 dB insertion loss at 800 Hz). Receiver manual override is disabled All other states of bits 2 to 4 are reserved and are not to be used until further defined Bit 5 Lock indication State 0 Default. Lock condition not indicated 1 Source sampling frequen
