Multichannel Audio Services
In 1995, IRT realised digital radio broadcasts in multichannel mode for the first time by means of the MPEG1 Layer2 format. Since then, IRT staff have been methodically tracking and assessing innovations in 5.1 multichannel formats such as Dolby Digital, Dolby Digital Plus, DTS, MPEG AAC, HE AAC, Windows Media, and MPEG Surround. We examine the possibility of integrating these formats into existing and new systems for the broadcasting of TV and radio services by conventional means and on the Internet. Our specialists conduct extensive testing of multichannel-ready set-top boxes, compile corresponding regulations for playout providers and manufacturers of set-top boxes, and explore the possibility of streaming multichannel audio on the Internet.
Analysing Audio Quality
IRT regularly carries out objective and subjective assessments of new 5.1 multichannel-audio coding schemes. As leader of the EBU project group B/MAE (Multichannel Audio System and Quality Evaluation), IRT is in a distinguished position to execute Europe-wide test programmes in conjunction with experts from other countries.
Mobile Reception with MPEG Surround
In cooperation with the BMW Group, IRT developed a design study for the transmission of 5.1 multichannel audio via DAB in the new MPEG Surround format. An innovative international standard, MPEG Surround facilitates the transmission of 5.1 multichannel audio which is backwards compatible to conventional stereo equipment. Moreover, its data rate is merely 10% higher than that of a high-quality stereo signal.
The additional channels – for the center, left, and right speakers as well as the LFE channel (Low Frequency Effect) – are produced with the aid of parametric data, which are entered in a compatible format into the field for supplementary data in the MPEG1 Layer II stereo signal. The resulting audio quality closely approximates the typically good quality achieved by conventional multichannel-audio coding schemes.
A bit rate of 15 to 20 kbit/s is usually required to code supplementary data for surround-sound applications. Whereas these supplementary data cannot be detected by conventional DAB units – which merely receive simple stereo signals – multichannel-ready receivers as per the MPEG Surround standard will, thanks to supplementary data, be able to extract from the stereo signal a 5.1 Surround Sound signal of sufficiently high quality for most applications. And motorists will soon be able to enjoy excellent 5.1 multichannel audio in their cars: the relatively low capacity of terrestrial transmission channels is ideal for MPEG Surround.
The Remarkable World of HDTV and 5.1 Multichannel Audio
The successful mixture of excellent multichannel audio and sharp HDTV picture quality guarantees a TV experience like no other. In conjunction with several broadcasters and the Film & Television Academy (HFF) in Brandenburg, Germany, IRT has in recent years produced a number of test films, which in turn enjoyed great success at various events such as the Tonmeistertagung, numerous HDTV workshops and IFA 2005. Feedback at these events made it clear that HDTV can realise its full potential only if equal attention is given to the quality of audio. This quite simply validates the decision to pursue 5.1 multichannel audio in the broadcasting sector. And in regard to high-quality sound, it is unnecessary to differentiate between SDTV and HDTV. After all, the same 5.1 audio format is compatible with both TV formats!
Further information on HDTV and Multichannel Audio
