1、 Recommendation ITU-R BS.1873(03/2010)Serial multichannel audio digital interface for broadcasting studiosBS SeriesBroadcasting service (sound)ii Rec. ITU-R BS.1873 Foreword The role of the Radiocommunication Sector is to ensure the rational, equitable, efficient and economical use of the radio-freq
2、uency 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 Radiocom
3、munication 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 pat
4、ent 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 Recommendation
5、s (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 relat
6、ed 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 Ti
7、me 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, 2010 ITU 2010 All rights reserved. No part of this publication may be reproduced,
8、by any means whatsoever, without written permission of ITU. Rec. ITU-R BS.1873 1 RECOMMENDATION ITU-R BS.1873 Serial multichannel audio digital interface for broadcasting studios (Question ITU-R 130/6) (2010) Scope This Recommendation specifies a serial multichannel sound digital interface to be use
9、d in broadcasting studios. The specification includes the data organization and electrical characteristics for the serial digital transmission of linearly represented digital data at a common sampling frequency over coaxial or fibre-optic lines. The ITU Radiocommunication Assembly, considering a) th
10、at Recommendation ITU-R BS.775 specifies one universal multichannel stereophonic sound system with three front channels and two rear/side channels together with an optional low frequency effects (LFE) channel; b) that a significant number of sound channels are generally used for sound programme prod
11、uction in broadcasting studios; c) that there is a need to interconnect multichannel sound signals between various pieces of digital sound equipment in broadcasting studios; d) that it is advantageous for all the equipment to use the same interface connections; e) that Recommendation ITU-R BS.647 A
12、digital audio interface for broadcasting studios, specifies the digital interface for the serial digital transmission of two channels of linearly represented digital sound data used in production for sound and television broadcasting; f) that Recommendation ITU-R BS.646 Source encoding for digital s
13、ound signals in broadcasting studios, defines the digital sound format used in production for sound and television broadcasting, recommends 1 that the interface described in Annex 1 should be used as a serial multichannel sound digital interface in broadcasting studios; 2 that compliance with this R
14、ecommendation is voluntary. However, the Recommendation may contain certain mandatory 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 s
15、uch 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 this Recommendation. 2 Rec. ITU-R BS.1873 Annex 1 Serial multichannel audio digital interface (MADI) 1 Introduction This annex spe
16、cifies the data organization and electrical characteristics for a multichannel audio digital interface for broadcasting studios. It includes a bit-level description, features in common with the two-channel format of Recommendation ITU-R BS.647 and the data rates required for its utilization. The spe
17、cification provides for the serial digital transmission over coaxial or fibre-optic lines of 56 or 64 channels of linearly represented digital data at a common sampling frequency within the range of 32 kHz to 48 kHz having a resolution of up to 24 bits per channel. Only single-point to single-point
18、interconnections from one transmitter to one receiver are supported. The interface specified here is primarily intended to be used at 48 kHz as this is the recommended sampling frequency for use in broadcasting studios according to Recommendation ITU-R BS.646. 2 Terminology For the purpose of this s
19、pecification the following definitions of terms apply. 2.1 Audio sample data Audio signal that has been periodically sampled, quantized, and digitally represented in 2s complement form. 2.2 Channel Set of audio sample data related to one signal accompanied by other data bits transmitted in any one p
20、eriod of the source sampling frequency. 2.3 Two-channel format Bit, block, and subframe structure (fewer preambles) of the Recommendation ITU-R BS.647 serial transmission format for linearly represented digital audio data. 2.4 Frame Sequence of 64 or less (typically 56) subframes designated using nu
21、mbers 0 to 63, each carrying audio sample and related data that are transmitted in one sample period, with the start of a frame beginning with the first bit of subframe 0. 2.5 Link Connection between a single serial multichannel digital audio transmitter and a single multichannel digital audio recei
22、ver. 2.6 Sync symbol Decoder synchronization symbol. Rec. ITU-R BS.1873 3 2.7 MADI Multichannel audio digital interface. 2.8 NRZI (Non-return to Zero, Invert on Ones) A technique in which a polarity transition represents a logical “1” (one). The absence of a polarity transition denotes a logical “0”
23、 (zero). 3 Format This specification provides for the serial digital transmission over coaxial or fibre-optic lines of 56 or 64 channels of linearly-represented digital data at a common sampling frequency within the range of 32 kHz to 48 kHz having a resolution of up to 24 bits per channel. See Fig.
24、 1. FIGURE 1 Diagram of MADI BS.1873-01ReceiverSynchronizationregeneratorTransmitterBuffer32ReceiverReceiverTransmitterClockReadTransmitterCrystalData4B/5BEncoderMastersynchronizationmDataClockgenerator32Crystalfs5B/4BDecoderClockSynchronizationregeneratorClocksynchro-nization32Datafsfsfs32DataBuffe
25、rSerial NRZI125 Mbit/s DataNote 1 As sample rate changes NRZI data rate stays constant; transmitter and receiver are asynchronous. Sampling frequencies (fs) are 32 kHz to 48 kHz.3.1 Frame format Each frame consists of n channels, which are numbered from 0 to n 1. The channels are consecutive within
26、the frame, starting with channel 0 as shown in Fig. 2. 4 Rec. ITU-R BS.1873 FIGURE 2 48 kHz with 56 channels working BS.1873-020Ch 0nAMADI subframeAudio channelSample numberRec. ITU-R BS.647subframe1Ch 1nB2Ch 2nA3Ch 3nB454Ch 54nA55Ch 55nB0Ch 0n + 1A20.8 sNote 1Note 2 Synchronization symbols not show
27、n. The period of each pattern is shown for the 48 kHz sampling frequency. It can be longer for lower frequencies and can vary with varispeed operation.3.2 Channel format Each channel consists of 32 bits, of which 24 are allocated to audio or to other data as defined by the audio/non-audio status fla
28、g. A further 4 bits represent the validity (V), user (U), status (C), and parity (P) bits of the Recommendation ITU-R BS.647 two-channel format interface, with a further 4 bits allocated for mode identification. In this manner, the Recommendation ITU-R BS.647 two-channel format is preserved. The cha
29、nnel format is shown in Fig. 3. FIGURE 3 Channel data format BS.1873-03ON/OFF (MADI channel active)Unencoded channel data bitsMADI subframe zeroRec. ITU-R BS.647 subframe A/BRec. ITU-R BS.647 block startRec. ITU-R BS.647CRec. ITU-R BS.647PRec. ITU-R BS.647URec. ITU-R BS.647VAudio data bit 27 = MSBMS
30、B01234567891011213141516171819202122324252627282930313.2.1 Mode bits The mode bits provide for frame synchronization, for block start per Recommendation ITU-R BS.647, for identification of the A and B subframes also present in Recommendation ITU-R BS.647, and for active/inactive status per channel.
31、3.2.2 Audio data representation In the audio mode, the 24-bit format is represented linearly in 2s complement form, with the most significant bit (MSB) transmitted last. All unused audio bits within a channel are set to zero, with the V, U, C, and P bits set to default values, as defined by the Reco
32、mmendation ITU-R BS.647 two channel format. 3.2.3 Active channels All active channels are consecutive, starting at channel zero. The channel active bit is set to 1 within each active channel. Rec. ITU-R BS.1873 5 3.2.4 Inactive channels All inactive channels have all bits set to zero, including the
33、channel active bit. Inactive channels always have a higher channel number than the highest numbered active channel. 3.2.5 Bit description See Tables 1 and 2. TABLE 1 Bit description Bit Name Description Sense 0 MADI subframe 0 Frame synchronization bit 1 = true 1 MADI channel active Channel active b
34、it 1 = true 2 “two channel format” subframe A/B “two channel format” subframe identifier 1 = B 3 “two channel format” block start First frame of “two channel format” block 1 = true 4 to 27 “two channel format” data bits (bit 27 is MSB) 28 “two channel format” V Validity bit 0 = valid 29 “two channel
35、 format” U User bit true to “two channel format” 30 “two channel format” C Channel status bit true to “two channel format” 31 “two channel format” P Parity bit (excludes bits 0 to 3) Even TABLE 2 Bits 2 to 3 compatibility with “two channel format” Bit 2 Bit 3 Two-channel form Description 0 0 Form 2
36、A subframe 0 1 Form 1 A subframe status block start 1 0 Form 3 B subframe 1 1 Form 4(1)B subframe status block start (1)Does not conform to the Recommendation ITU-R BS.647 two-channel format. 3.3 Transmission format 3.3.1 4B5B coding The channels are transmitted serially. The binary sequence is reco
37、ded from 100 Mbit/s to 125 Mbit/s by replacing every 4 source bits with a unique 5-bit sequence specified in 3.3.1.1. This scheme is known as 4B5B coding. NOTE 1 The purpose of this new code is that it contains no continuous sequences of ones or zeros. 6 Rec. ITU-R BS.1873 3.3.1.1 Encoding scheme Fo
38、r the purposes of encoding, the 32-bit channel data are broken down into 8 words of 4 bits each, as shown in Table 3. TABLE 3 32-bit channel data Word Channel data bit 0 01231 4567 2 893 4 5 6 7 .31 Each 4-bit word is encoded into a 5-bit word using the 4B5B coding scheme shown in Table 4. TABLE 4 5
39、-bit word coding 4-bit data 5-bit encoded data 0000 11110 0001 010010010 10100 0011 101010100 01010 0101 010110110 01110 0111 011111000 10010 1001 100111010 10110 1011 101111100 11010 1101 110111110 11100 1111 11101Rec. ITU-R BS.1873 7 Each 5-bit encoded word is transmitted from the left, as defined
40、 in Table 5. TABLE 5 5-bit word transmission Word Channel data bit 0 012341 56789 2 .3 . 4 .5 . 6 .7 39 3.3.2 4B5B synchronization symbol (sync symbol) A 4B5B sync symbol is inserted into the data stream at least once per frame period to ensure transmitter and receiver synchronization of the 4B5B de
41、coder in the receiver. Sufficient 4B5B sync symbols are inserted by interleaving with the encoded data words to fill the total link capacity. The 4B5B sync symbol is transmitted from the left. The 4B5B sync symbol may only be inserted at 40-bit channel boundaries, but may be repeated between channel
42、s or during the idle period after the last channel has been transmitted in each frame capacity, or both. The order placement of 4B5B sync symbols is not specified. Some examples of permissible positions of the 4B5B sync symbol are shown in Fig. 4. FIGURE 4 Some permissible 4B5B sync symbol positions
43、 BS.1873-04Start of frameChannel 0 Channel 1 Channel 2Sync SyncChannel N Channel 1N + Channel 2N +Sync Sync SyncChannel 54 Channel 55 Channel 0 (next frame)Sync Sync SyncEnd of frameThe default 4B5B sync symbol is 11000 10001. There are 32 synchronization symbols specified in FDDI. Other symbols may
44、 be used in order to carry, for example, control data not associated with any audio channel. Annex A to Annex 1 outlines this function. 8 Rec. ITU-R BS.1873 3.3.3 Sequence of transmission In any bit sequence, the left-hand symbol always represents the first in time. 3.3.4 NRZI transmission The resul
45、tant 125 Mbit/s bit stream is transmitted by the polarity-independent technique known as NRZI. This scheme enables a low direct-current (d.c.) bias to be maintained on the link. Although the link signal is nearly d.c. free, the audio signal may contain d.c. Figure 5 shows the link transmission forma
46、t for one channel. Appendix A to Annex 1 illustrates the encoding process for a single-channel word. FIGURE 5 Channel link format BS.1873-050123456789101121314151617181920212223242526 3233 37383927 28 29 30 31 32 33 34 35 36Encoded channel link bits3.3.5 Control data carriage This section describes
47、in outline a method of carrying control data in the transport carrier independent of any particular audio channel. The transport sync symbol words inserted between audio data words can carry this control data by virtue of the fact that there are a number of forms of sync symbol, of which the default
48、 is that used by MADI systems. Four-bit nibbles are associated with 16 of the sync symbol forms, thus allowing data to be inserted in the available space. The default sync symbol described in 3.3.2 is associated with the binary value 0000. A stream of 56 channels at 48 kHz 12.5% and highest permitte
49、d varispeed rate uses 96.768 Mbit/s, and a 64-channel 48 kHz stream uses 98.304 Mbit/s. Thus there will always be at least 1 Mbit/s for this data. This may need to be reduced to ensure that bit-stream synchronization is maintained. 3.3.5.1 Data insertion 3.3.5.1.1 Ordering Default sync symbol words are transmitted at least as often as required, in order to guarantee correct data recovery of the whole transport stream. Coded sync symbols are inserted as and when required, subject to the needs of audio data and the provision above. 3.3.5.1.2 Data coding A format relatin
