1、 Recommendation ITU-R BS.775-3(08/2012)Multichannel stereophonic sound system with and without accompanying pictureBS SeriesBroadcasting service (sound)ii Rec. ITU-R BS.775-3 Foreword The role of the Radiocommunication Sector is to ensure the rational, equitable, efficient and economical use of the
2、radio-frequency 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 Regiona
3、l Radiocommunication 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 submiss
4、ion of 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 Reco
5、mmendations (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
6、 and related 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 gathe
7、ring TF 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, 2012 ITU 2012 All rights reserved. No part of this publication may be re
8、produced, by any means whatsoever, without written permission of ITU. Rec. ITU-R BS.775-3 1 RECOMMENDATION ITU-R BS.775-3*, *Multichannel stereophonic sound system with and without accompanying picture (1992-1994-2006-2012) Scope Digital TV has rapidly gained ground around the world. Several digital
9、 television broadcasting services have already been introduced in the terrestrial and in the satellite bands. As part of these digital broadcasting services, multichannel audio services are used or have been specified to enhance the directional stability of the frontal sound image and the sensation
10、of spatial reality (ambience). Recommendation ITU-R BS.775 recommends one universal multichannel stereophonic sound system with three front channels and two rear/side channels together with an optional low frequency effects (LFE) channel. The ITU Radiocommunication Assembly, considering a) that it i
11、s widely recognized that a two-channel sound system has serious limitations and improved presentation is necessary; b) that the requirements of cinema presentation differ from those that apply in the home, particularly with respect to room and screen size and distribution of listeners, but that the
12、same programmes may be reproduced in either the cinema or the home; c) that broadcast HDTV signals, and those delivered by other media, should be capable of giving appropriate sound quality with a wide range of domestic loudspeaker configurations, including compatibility with two-channel stereophoni
13、c and monophonic listening; d) that for multichannel sound it is desirable to separate the requirements of production, delivery and domestic presentation, though these are mutually interacting; e) that investigations about multichannel sound transmission and reproduction associated and not associate
14、d with accompanying picture are being carried out with the basic requirements; f) that one universal multichannel sound system applicable to both sound and television broadcasting would be beneficial to the listener; g) that compromises may be necessary to ensure that the system is as universal and
15、as practical as possible; h) that a hierarchy of compatible sound systems for broadcasting, cinema and recordings is useful for programme exchange and up- and down-mixing depending on the programme material; *This Recommendation should be brought to the attention of the International Electrotechnica
16、l Commission (IEC) and the Society of Motion Picture and Television Engineers (SMPTE). *Radiocommunication Study Group 6 made editorial amendments to this Recommendation in November 2009 in accordance with Resolution ITU-R 1. 2 Rec. ITU-R BS.775-3 j) that ancillary services such as those for the vis
17、ually impaired and hearing impaired are desirable; k) that advances in digital audio coding currently allow the delivery of multiple audio channels in an efficient manner, recommends 1 the universal multichannel stereophonic sound system, with or without accompanying picture, within a hierarchy give
18、n in Annex 1; 2 the following reference loudspeaker arrangement (see Fig. 1): three front loudspeakers combined with two rear/side loudspeakers (Note 1); the left and right frontal loudspeakers are placed at the extremities of an arc subtending 60 at the reference listening point (Notes 2 and 3). Wh
19、ere for reasons of available space, it is preferred to place the frontal loudspeakers on a straight line base, then it may be necessary to introduce compensating time delays in the signal feed of the centre loudspeaker; both side/rear loudspeakers should be placed within the sectors from 100 to 120
20、from the centre front reference. Precise location is not necessary. Side/rear loudspeakers should be no closer to the listener than the frontal loudspeakers, unless compensating time delay is introduced (Notes 4 and 5); the acoustic centre of frontal loudspeakers should ideally be at a height approx
21、imately equal to that of the listeners ears. This implies an acoustically transparent screen. Where a non-acoustically transparent screen is used, the centre loudspeaker should be placed immediately above or below the picture. The height of side/rear loudspeakers is less critical; 3 the use of five
22、reference recording/transmission signals for left (L), right (R), centre (C), channels for the front, and left surround (LS) and right surround (RS) channels for the side/rear. Additionally the system may include a low frequency effects signal for a low frequency effects (LFE) channel any use of whi
23、ch should take into account the information provided in Annex 7 and Appendix 1 of Annex 7. In circumstances where transmission capacity or other constraints apply, the LS and RS signals can be combined with one (mono surround, MS) or zero rear/side signals. In the case of mono surround, the MS signa
24、l is fed to both LS and RS loudspeakers (see Fig. 1); 4 that in the international exchange of audio or television programmes that use an audio format which offers a low-frequency effects (LFE) channel, the LFE channel should be band-limited to its nominal frequency band (up to120 Hz); 5 that broadca
25、st of any television programme that contains an LFE channel should not transmit any information on that channel above the nominal 120 Hz cutoff frequency; 6 compatibility, if required, with existing and low cost receivers by using one of the methods given in Annex 3; 7 down-mixing capability, if req
26、uired, for reduction of the number of channels, either prior to transmission or at the receiver, by employing the down-mixing equations given in Table 2; 8 upward conversion where an increase in the number of channels is desired, either prior to transmission or at the receiver, by employing upwards-
27、conversion techniques described in Annex 5; 9 overall quality to the requirements of Annex 2; Rec. ITU-R BS.775-3 3 10 provision (but see also 11 below) for the following if necessary: alternate multiple language principal services; one or more independent channels carrying descriptive information f
28、or the visually impaired; one or more independent channels for the purpose of supplying improved intelligibility to the hearing impaired; 11 additional data transmitted with the audio to enable the flexible use of the data capacity allocatable to audio signals (see Annex 6). 4 Rec. ITU-R BS.775-3 FI
29、GURE 1 Reference loudspeaker arrangement with loudspeakers L/C/R and LS/RS BS.0775-0110010012012060RLLS21CB12RSLoudspeakerHorizontal angle fromcentre (degrees)Height(m)Inclination(degrees)CL, RLS, RS030100 . 120 0 . 15 down001.21.2 1.2Screen 1 HDTV Reference distanceScreen 2H: height of screenB: lou
30、dspeaker base width= 3 (2H = 33)= 2 (2 H = 48)12NOTE 1 Optionally, there may be an even number of more than two rear/side loudspeakers which may provide a larger optimum listening area and greater envelopment. NOTE 2 Optimum sound reproduction requires use of wide angular spacing between the left an
31、d right loudspeakers of two or three front loudspeaker channel stereophonic systems (see Fig. 1). It is recognized that the television pictures accompanying stereophonic sound having such an angular width cannot, with current techniques, be displayed to the same wide angles, but are often restricted
32、 to 33 horizontal subtended angle at the reference distance, although cinema images may be displayed at such angles (see Fig. 1). The Rec. ITU-R BS.775-3 5 resulting mismatch between picture and sound image width leads to differences in mixing technique for cinema and television. It is expected that
33、 larger television displays will lead to better compatibility of mixes for cinema and television display. NOTE 3 The size of the loudspeaker basewidth, B (see Fig. 1), is defined for reference listening test conditions in Recommendation ITU-R BS.1116 Methods for the subjective assessment of small im
34、pairments in audio systems including multichannel sound systems. NOTE 4 If more than two rear/side loudspeakers are used, then the loudspeakers should be disposed symmetrically and at equal intervals on the arc which measures from 60 to 150 from the centre front reference (see Fig. 2). NOTE 5 If mor
35、e than two rear/side loudspeakers are used, the LS signal should be fed to each of the side/rear loudspeakers on the left side of the room and the RS signal should be fed to each of the side/rear loudspeakers on the right side of the room. In doing so, it will be necessary to reduce the signal gain
36、such that the total power emitted by the loudspeakers carrying the LS (or RS) signal is the same as if that signal had been reproduced over a single loudspeaker. For large room reproduction, it may also be necessary to delay, or otherwise de-correlate, the feeds to some or all of the side/rear louds
37、peakers. Further studies on such de-correlation is necessary. FIGURE 2 Optional 3/4 loudspeaker arrangement (3 front and 4 surround) BS.0775-0215060LCB1506060RLS1RS1LS2RS26 Rec. ITU-R BS.775-3 Annex 1 Hierarchy of compatible multichannel sound systems for broadcasting and recording BS.0775-A1RL(MS)
38、(MS)LS RS(1) (1)MMSMS(1) (1)RL60(MS) (MS)LS RS(1) (1)CMSystem Channels Code Loudspeaker arrangementMono channel systemMono plus mono surroundTwo-channel stereoTwo-channel stereo plus 2 surroundThree-channel stereo plus 1 surrondThree-channel stereo plus 2 surroundTwo-channel stereo plus 1 surroundTh
39、ree-channel stereo MM/MSL/RL/R/MSL/R/LS/RSL/C/RL/C/R/MSL/C/R/LS/RS1/01/12/02/13/03/23/12/2In the case of mono surround the signal feeding LS and RS should preferably be decorrelated.(1)Rec. ITU-R BS.775-3 7 Annex 2 Basic requirements The following requirements are related to the specified multichann
40、el sound system with and without accompanying picture. 1 The directional stability of the frontal sound image shall be maintained within reasonable limits over a listening area larger than that provided by conventional two-channel stereophony. 2 The sensation of spatial reality (ambience) shall be s
41、ignificantly enhanced over that provided by conventional two-channel stereophony. This shall be achieved by the use of side and/or rear loudspeakers. 3 It is not required that the side/rear loudspeakers should be capable of the prescribed image locations outside the range of the front loudspeakers.
42、4 Downward compatibility with sound systems providing lower number of channels (down to stereophonic and monophonic sound systems) shall be maintained (see Annexes 1, 3, 4 and 8). 5 Real-time mixing for live broadcast shall be practicable. 6 In cases where the number of delivered signals is smaller
43、than the number of reproduction channels upward conversion should be ensured to an acceptable degree (see Annex 5). 7 The basic audio quality of the sound reproduced after decoding shall be subjectively indistinguishable from the reference for most types of audio programme material. Using the triple
44、 stimuli with hidden reference test implies grades consistently higher than four on the ITU-R impairment 5-grade scale. The most critical material shall not be graded lower than four. For subjective assessments and listening test conditions see Recommendation ITU-R BS.1116. 8 For the objective quali
45、ty parameters Recommendations ITU-R BS.644 and ITU-R BS.645 shall be the basis for digital techniques. For objective measurements method of perceived audio quality for mono or two-channel stereo sound see Recommendation ITU-R BS.1387. (The objective measurements method for multichannel stereophonic
46、sound is under study by ITU-R.) 9 Relative timing of the synchronization of sound and vision signals see Recommendation ITU-R BT.1359. 10 Optimum economy shall be pursued in all respects, including both cost and transmission bandwidth. 11 For user requirements for audio coding systems for digital br
47、oadcasting see Recommendation ITU-R BS.1548. 8 Rec. ITU-R BS.775-3 Annex 3 Compatibility 1 Backward compatibility with existing receivers In the case that an existing 2/0 channel format is extended to a 3/2 channel format, two methods have been identified to assure backward compatibility with existi
48、ng receivers. One method is to continue providing the existing 2/0 channel service and to add the new 3/2 channel service. This approach is referred to as a simulcasting operation. The advantage of this approach is that the existing 2/0 service could be discontinued at some point in the future. Anot
49、her method is the use of compatibility matrices. The matrix equations shown in Table 1 may be used to provide compatibility with existing receivers. In this case, the existing Left and Right emission channels are used to convey the compatible A and B matrix signals. Additional emission channels are used to convey the T, Q1, and Q2matrix signals. The advantage of this approach is that less additional data capacity is required to add the new service. TABLE 1 Five channel surround: encoding and decoding equations 2 Downward compatib
