1、 Recommendation ITU-R BS.1548-4(01/2013)User requirements for audio coding systems for digital broadcastingBS SeriesBroadcasting service (sound)ii Rec. ITU-R BS.1548-4 Foreword The role of the Radiocommunication Sector is to ensure the rational, equitable, efficient and economical use of the radio-f
2、requency 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 Radio
3、communication 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
4、patent 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 Recommendat
5、ions (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 re
6、lated 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
7、 Time 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 reproduce
8、d, by any means whatsoever, without written permission of ITU. Rec. ITU-R BS.1548-4 1 RECOMMENDATION ITU-R BS.1548-4*User requirements for audio coding systems for digital broadcasting (Question ITU-R 19-1/6) (2001-2002-2006-2012-2013) Scope This Recommendation specifies the requirements relevant to
9、 the use of audio source coding systems in sound broadcasting, including television. The Recommendation covers the application of contribution and distribution, and emission. The ITU Radiocommunication Assembly, considering a) that the multichannel sound system, with or without accompanying picture,
10、 is the subject of Recommendation ITU-R BS.775; b) that audio coding for digital broadcasting is the subject of Recommendation ITU-R BS.1196; c) that the coding systems recommended in Recommendation ITU-R BS.1196 offer monophonic, two-channel stereophonic and multichannel coding modes; d) that the b
11、asic audio and stereo image quality required for sound systems for television and sound broadcasting is to be the highest possible, generally indistinguishable from the source material; e) that required audio quality for some emission applications is to be equivalent to or better than good reception
12、 of FM or AM analogue broadcasting services; f) that Recommendation ITU-R BS.1283 provides a guide to ITU-R Recommendations for subjective assessment of sound quality; g) that interoperability and network operation involving programme connections such as contribution and distribution links should be
13、 carefully considered; h) that interoperability with existing consumer multichannel audio equipment, such as matrix surround decoders and discrete multichannel decoders, should be carefully considered; j) that, when introducing a multichannel sound system in an existing broadcasting service, compati
14、bility with existing receivers to maintain the service must be considered; k) that more generally, in view of the many applications of such systems, all technical, quality and operational requirements should be clearly specified; l) that the performance of audio coding systems is widely dependent on
15、 the configuration under which the system is operated (bit rate, use of pre-matrixing, use of composite coding, etc.); m) that several broadcast services already use or have specified the use of the systems recommended in Recommendation ITU-R BS.1196; *Radiocommunication Study Group 6 made editorial
16、 amendments to this Recommendation in November 2009 and October 2010 in accordance with Resolution ITU-R 1. 2 Rec. ITU-R BS.1548-4 n) that, consequently, the broadcasters have a need of information necessary to set up all the available coding parameters of the recommended systems; o) that the introd
17、uction of incompatible systems with similar performance characteristics is highly undesirable; p) that those broadcasters which have not yet started services should be able to choose the system which is best suited to their application and which is the most cost-effective, recommends 1 that the audi
18、o coding systems for digital television and sound broadcasting for contribution and distribution applications should fulfil the requirements listed in Annex 1; 2 that the audio coding systems for digital television and sound broadcasting for emission applications should fulfil the requirements liste
19、d in Annex 2; 3 that the categories of audio quality listed in Annex 3 should govern the audio quality and applications in recommends 1 and 2. NOTE 1 Information about systems that have been shown to meet the quality and other requirements for contribution and distribution applications is included i
20、n Appendix 1 to Annex 1. NOTE 2 Information about systems that have been shown to meet the quality and other requirements for emission applications is included in Appendix 1 to Annex 2. Annex 1 Requirements for contribution and distribution The audio coding systems for digital television and sound b
21、roadcasting for both contribution and distribution applications should fulfill the requirements listed below. 1 Service requirements 1.1 Channel configurations For audio services the following channel configurations should be supported according to the needs of applications (see Recommendation ITU-R
22、 BS.775 Multichannel sterophonic sound system with and without accompanying picture): Rec. ITU-R BS.1548-4 3 No. of channels Channel configuration Channel assignment 1 channel 1/0 Mono 2 channels 2/0 Left, right 3 channels 3/0 2/1 Left, right, centre Left, right/surround 4 channels 3/1 2/2 Left, rig
23、ht, centre/surround Left, right/surround left, surround right 5 channels 3/2 Left, right, centre/surround left, surround right together with an optional low frequency effects (LFE) channel. For contribution, in addition, it could be necessary to convey programmes produced in other formats than those
24、 listed above, e.g. 3/4, thus the coding system should allow for accommodation of additional high quality channels. 1.2 Flexible allocation of channels A bit stream should provide identification data for signalling and controlling of sound configurations. It must be possible in the transmission syst
25、em to switch dynamically among the channel configurations listed in 1.1. 1.3 Ancillary data The audio coding system should provide for the possibility of transmission of ancillary data. The ancillary data can convey various types of information, including dynamic range control, loudness control, use
26、r data, and any metadata required by the emission encoder that will encode the final audio for delivery to the consumer. 2 Performance requirements 2.1 Audio quality 2.1.1 Basic audio quality The quality of sound reproduced after a reference contribution/distribution cascade (five contribution codec
27、s and three distribution codecs working consecutively) should be subjectively indistinguishable from the source for most types of audio programme material. Using the triple stimuli double blind with hidden reference test, described in Recommendation ITU-R BS.1116 Methods for the subjective assessmen
28、t of small impairments in audio systems including multichannel sound systems this requires mean scores generally higher than 4.5 in the impairment 5-grade scale, for listeners at the reference listening position. The worst rated item should not be graded lower than 4 (Recommendation ITU-R BS.775). N
29、OTE 1 The confidence interval (error bar) associated with the single mean score for a codec and item shows the range above and below the stated mean score in which the true score may fall, with some degree of certainty, usually 95%. The true score for a codec and item may be as poor as the lower lim
30、it of the confidence interval about the stated score. In order to make a meaningful evaluation of the expected performance of cascaded codecs, the confidence interval associated with the reported mean scores for the 4 Rec. ITU-R BS.1548-4 individual codecs must be approximately equal to or less than
31、 the difference between the scores being compared. NOTE 2 The contribution/distribution cascade, when placed in tandem with the emission codec, should not cause a significant reduction in quality compared to the basic audio quality of the emission codec. Precise specification requires further study.
32、 NOTE 3 The objective audio quality parameters for contribution/distribution can be incorporated later, conforming to Recommendation ITU-R BS.1387. 2.1.2 Quantization resolution The required resolution should be at least 18 bits for distribution and 20 bits or greater is preferable for contribution.
33、 2.1.3 Sampling frequency In agreement with Recommendation ITU-R BS.646 Source encoding for digital sound signals in broadcasting studios, the sampling frequency should be 48 kHz. 2.1.4 Bandwidth Main audio channels: 20-20 000 Hz. LFE channel: 15-120 Hz. 2.1.5 Emphasis The audio coding system should
34、 be emphasis free. 2.1.6 Tandem capability The tandem capability required depends on the application according to the following table: These figures have been taken from previous experiments done to evaluate two-channel sound broadcasting systems (see Recommendation ITU-R BS.1196 Audio coding for di
35、gital broadcasting) and may not be representative of the practical radio and television broadcasting operational situations. More information is required to specify this aspect better. 2.1.7 Post-processing capability The post-processing capability required is strongly dependent on the application.
36、For distribution crossfades can be applied together with dynamic range control. 2.2 Coding delay Coding delay for all channels in a programme must be identical. The coding delay should be as low as possible, considering the coding performance (i.e. amount of bit rate reduction) required. In case of
37、television sound, the delay of audio must be matched with the delay of video. It is desirable that the audio coder produces encoded audio frames (access units) that correspond exactly to the time period of the matching video frame. Distribution 3 codecs in cascade Contribution 5 codecs in cascade Re
38、c. ITU-R BS.1548-4 5 2.3 Error resilience A mechanism must be provided in the audio bit stream to allow the decoder to identify residual channel errors and to adopt proper concealment methods. 2.4 Recovery time The recovery time should be as low as possible. In case of audio access unit (AAU) applie
39、d, the recovery time should be within a few AAU, and preferably the audio should resume upon receipt of the first error free AAU. 3 Functional and operational requirements 3.1 Bit rate and coding scheme For distribution and contribution links, Recommendation ITU-R BS.1196 recommends the Internationa
40、l Organization for Standardization/International Electrotechnical Commission (ISO/IEC) IS 11172-3 Layer II at a bit rate of 180 kbit/s per channel or above. For several reasons the system may be applied at a different bit rate or other systems may be employed. These reasons may include the following
41、: additional coding margin to support signal processing that may be inserted between coding generations (this was not tested or verified in the development of Recommendation ITU-R BS.1196); to obtain a lower bit rate in the distribution and contribution link; to obtain a higher quality; suitability
42、of synchronization and switching with accompanying video signals. 3.2 Composite coding Two-channel or multichannel programme material often contains some inter-channel statistical correlation. Composite coding can be an effective way to reduce the inter-channel irrelevance or redundancy, thus increa
43、sing the coding efficiency. Some coding systems use perceptual criteria to eliminate part of the inter-channel irrelevance by joining together two or more channels in frequency regions where the ability of the human ear to discriminate the direction of the source is poor. The disadvantage of this te
44、chnique is that it is not possible to correctly reposition the sound information generally in the original channels at a later stage. For contribution and many distribution applications such composite coding schemes should not be used. 6 Rec. ITU-R BS.1548-4 Appendix 1 to Annex 1 (Informative) Infor
45、mation about coding systems that have been demonstrated to meet quality, and other, user requirements for contribution and distribution Table 1 lists, in the left-hand column, the requirements specified in Annex 1. The right-hand column shows the ability of a specific codec to meet these requirement
46、s. It is anticipated that future revisions to this Recommendation will contain additional information about additional codecs. TABLE 1 List of requirements from Annex 1 Codec: Dolby E ref. 1 1.1 Channel configurations Fulfilled ref. 1, p. 6 1.2 Flexible channel allocation Fulfilled ref. 1, p. 15 1.3
47、 Ancillary data Fulfilled ref. 1, p. 14 2.1.1 Basic audio quality Fulfilled ref. 2 2.1.2 Quantization Fulfilled ref. 1, p. 5 2.1.3 Sampling frequency Fulfilled ref. 1, p. 5 2.1.4 Bandwidth Fulfilled ref. 1, p. 9 2.1.5 Emphasis Fulfilled ref. 1 2.1.6 Tandem capability Fulfilled ref. 2 2.1.7 Post proc
48、essing Not demonstrated 2.2 Coding delay Fulfilled(1)ref. 1, p. 7 2.3 Error resilience Fulfilled ref. 1, p. 15 2.4 Recovery time Fulfilled ref. 1, p. 15 3.1 Bit rate and coding Fulfilled(2)ref. 1, p. 6 3.2 Composite coding Fulfilled ref. 1 (1)To facilitate operation with television sound, the encode
49、 or decode delay is identical to a corresponding video frame rate (1/24, 1/25, 1/30 s). Access units correspond to video frames. (2)The bit rate/channel is 250 kbit/s in order to obtain the advantages indicated in the first, third, and fourth bullets under 3.1. Rec. ITU-R BS.1548-4 7 References 1 FIELDER, L. D., LYMAN, S. B., VERNON, S. and TODD, C. C. September 1999 Professional audio coder optimized for use with video. 107thAES Convention, New York, NY, United States of America. 2 GRANT, D., DAVIDSON, G. and FIELDER, L.
