a) that digital terrestrial television broadcasting will be introduced in the VHF/UHF bands;
b) that a high-quality, multi-channel sound system using efficient bit rate reduction is essential in such a system;
c) that bit rate reduced sound systems must be protected against residual bit errors from the channel decoding and demultiplexing process;
d) that multi-channel sound system with and without accompanying picture is the subject of Recommendation ITU R BS.775;
e) that subjective assessment of audio systems with small impairments, including multi-channel sound systems is the subject of Recommendation ITU R BS.1116;
f) that commonality in audio source coding methods among different services may provide increased system flexibility and lower receiver costs;
g) that digital sound broadcasting to vehicular, portable and fixed receivers using terrestrial transmitters in the VHF/UHF bands is the subject of Recommendations ITU R BS.774 and ITU R BS.1114;
h) that generic audio bit rate reduction systems have been studied by ISO/IEC in liaison with ITU R and that this work has resulted in IS 11172-3 (MPEG 1 audio) and IS 13818-3 (MPEG 2 audio) and are the subject of Recommendation ITU R BS.1115;
j) that several satellite sound broadcast services and many secondary distribution systems (cable television) use or have specified as part of their planned digital services MPEG 1 audio, MPEG 2 or AC 3 (see Annexes) multi channel audio;
k) that IS 11172-3 (MPEG 1 audio) and 13818 3 (MPEG 2 audio) are widely used in a range of equipment;
l) that an important digital audio film system uses AC 3;
m) that the European Digital TV Systems (DVB) will use MPEG 2 audio;
n) that the North-American Digital Advanced TV (ATV) system will use AC 3;
o) that interoperability with other media such as optical disc using MPEG 2 audio and/or AC 3 is valuable,
1 that digital terrestrial television broadcasting systems should use for audio coding the International Standard specified in Annex 1 or the U.S. Standard specified in Annex 2.
NOTE 1 – It is noted that the audio bit rates required to achieve specified quality levels for multi-channel sound with these systems have not yet been fully evaluated and documented in the ITU R.
NOTE 2 – It is further noted that there are compatible enhancements under development (e.g. further exploitation of available syntactical features and improved psycho-acoustic modelling) that have the potential to significantly improve the system performance over time.
NOTE 3 – Recognizing that the evaluation of the current, and future, performance of these encoding systems is primarily a concern of Radiocommunication Study Group 6, this Study Group is encouraged to continue its work in this field with the aim of providing authoritative addition on the Recommendation, and to detail the performance characteristics of coding options available, as a matter of urgency.
NOTE 4 – The audio coding system specified in Annex 2 is a non-backwards compatible (NBC) codec which is not backwards compatible with the two channel coding according to Recommendation ITU R BS.1115.
NOTE 5 – Radiocommunication Study Group 6 is encouraged to continue its work, to develop a unified coding specification.
two channel and multi channel sound for digital video broadcasting,
digital audio broadcasting and computer multimedia
From 1988 to 1992 the International Organization for Standardization (ISO) has been developing and preparing a standard on information technology – Coding of Moving Pictures and Associated Audio for Digital Storage Media up to about 1.5 Mbit/s. The “Audio Subgroup” of MPEG had the responsibility for developing a standard for generic coding of PCM audio signals with sampling rates of 32, 44.1 and 48 kHz at bit rates in a range of 32 192 kbit/s per mono and 64 384 kbit/s per stereo audio channel. The result of that work is the audio part of the MPEG 1 standard which consists of three layers with different complexity for different applications, and is called ISO/IEC 11172-3. After intensive testing in 1992 and 1993, ITU R recommends the use of MPEG 1 layer II for contribution, distribution and emission which are typical broadcasting
applications. Regarding telecommunication applications, ITU T has defined the Recommendation J.52 which is the standard for the transmission of MPEG audio data via ISDN.
The first objective of MPEG 2 audio was the extension of the high quality audio coding from two to five channels in a backwards compatible way, and based on Recommendations from ITU R, Society of Motion Picture and Television Engineers (SMPTE) and the European Broadcasting Union (EBU). This has been achieved in November 1994 with the approval of ISO/IEC 13818 3, known as MPEG 2 audio. This standard provides high quality coding of 5.1 audio channels, i.e. five full bandwidth channels plus a narrow bandwidth low frequency enhancement channel, together with backwards compatibility to MPEG 1 – the key to ensure that existing 2 channel decoders will still be able to decode the compatible stereo information from multi-channel signals. For audio reproduction of surround sound the loudspeaker positions left, centre, right, left and right surround are used – according to the 3/2-standard. The envisaged applications are beside digital television systems such as dTTb, HDTVT, HD-SAT, ADTT, digital storage media, e.g. the Digital Video Disc and Recommendation ITU-R BS.1114 Digital Audio Broadcasting system (EU147).
The second objective of MPEG-2 audio was the extension of MPEG-1 audio to lower sampling rates to improve the audio quality at bit rates less than 64 kbit/s per channel, in particular for speech applications. This is of particular interest for narrow band ISDN applications where for simple operational reasons multiplexing of several B channels can be avoided by still providing an excellent audio quality even with bit rates down to 48 kbit/s. Another important application is the EU147 DAB system. The programme capacity of the main service channel can be increased by applying the lower sampling frequency option to high quality news channels which need less bits for the same quality compared to the full sampling frequency.