INTERNATIONAL ORGANISATION FOR STANDARDISATION
ORGANISATION INTERNATIONALE DE NORMALISATION
ISO/IEC JTC1/SC29/WG11
CODING OF MOVING PICTURES AND AUDIO

ISO/IEC JTC1/SC29/WG11
N3084
December 1999 / Maui

Source: Audio Subgroup
Title: MPEG Audio FAQ
Authors: D. Thom, H. Purnhagen, S. Pfeiffer, and the MPEG Audio Subgroup

MPEG Audio FAQ

Who is the target audience of this FAQ?

This FAQ answers questions of people interested in the audio parts of the MPEG standards as well as giving some hints on how to get actively involved in the standardisation work. The answers also give a technical introduction to the different standards and how they compare to other standards in similar domains.

Content

1. MPEG-1 Audio: coded storage of sampled sound waves
   • Overview of MPEG-1
   • MPEG-1 language and abbreviations
   • Technicalities of MPEG-1
   • Implementing MPEG-1 audio software
   • Market position
   • Relation to other standards / methods
   • Bibliographic references
   • Organisational details
2. MPEG-2 Audio: coded transmission/storage of sampled sound waves
   • Overview of MPEG-2
   • MPEG-2 language and abbreviations
   • Technicalities of MPEG-2
   • Implementing MPEG-2 audio software
   • Market position
   • Relation to other standards / methods
   • Bibliographic references
   • Organisational details
3. MPEG-4 Audio: coding of natural and synthetic sound
   • Overview of MPEG-4
   • MPEG-4 language and abbreviations
   • Technicalities of MPEG-4
   • Implementing MPEG-4 audio software
   • Relation to other standards / methods
   • Bibliographic references
   • Organisational details
4. MPEG-7 Audio: description of meta-information on sound
   • Overview of MPEG-7
   • MPEG-7 language and abbreviations
   • Technicalities of MPEG-7
   • Relation to other standards / methods
   • Bibliographic references
   • Organisational details

MPEG Audio: general questions

What does "MPEG" stand for?

Moving Picture Experts Group.
Official Website: http://www.cselt.it/mpeg/

What is MPEG, what do they do?

MPEG is a working group in a subcommittee of ISO/IEC (International Organization for Standardization / International Electrotechnical Commission) in charge of developing international standards for compression, decompression, processing, and coded representation of moving pictures, audio, and their combination.
In particular, MPEG defines the syntax of low bitrate video and audio bitstreams of synthetic and natural sources, descriptions of their structure and content, and the operation of conformant decoders of these bitstreams. The encoder algorithms are not defined by MPEG. This allows for continuous improvement of encoders and their adaptation to specific applications, within the bitstream syntax definition. Along with the video and audio coding, MPEG also defines means to multiplex several video, audio and information streams synchronously in one single bitstream, describes methods to test conformance of bitstreams and decoders to the standard, and publishes technical reports containing software describing the decoder operation and software describing examples of encoder operation.

What is MPEG Audio?

MPEG Audio is a subgroup of MPEG working on all audio aspects of the MPEG standards.
Official Website: http://www.tnt.uni-hannover.de/project/mpeg/audio/

Talking about MPEG Audio, I hear about phases, versions, layers and levels. What does that all mean?

There are two different matters that have to be distinguished. First, MPEG works in phases. These phases are normally denoted by Arabic numbers (MPEG-1, MPEG-2, MPEG-4, MPEG-7). These phases do not describe different versions of one standardisation effort, but are rather completely different coexisting standards that all handle different aspects of Multimedia communication. Therefore, the later phases will NOT replace the earlier phase but complement them.

The second matter concerns the notion of layers. Both in MPEG-1 and in MPEG-2 BC, three different layers are defined, sometimes incorrectly called 'levels'. These layers represent a family of coding algorithms. The layers are preferably denoted by roman figures, i.e. Layer I, Layer II and Layer III. Refer to the subparts on MPEG-1 and MPEG-2 for details.

The notion of versions is used in the context of MPEG-4. Version 1 of MPEG-4 provides a set of tools for audio coding. With Version 2, new tools are added to provide additional functionality, while none of the existing tools of Version 1 is replaced. Version 2 is therefore fully backward compatible to Version 1. Refer to the subpart on MPEG-4 for details.

What is provided by MPEG-1, MPEG-2, MPEG-4 and MPEG-7 Audio?

MPEG-1 (ISO/IEC 11172-3) provides

• single-channel ('mono') and two-channel ('stereo' or 'dual mono') coding of digitized sound waves at 32, 44.1, and 48 kHz sampling rate. The predefined bitrates range from 32 to 448 kbit/s for Layer I, from 32 to 384 kbit/s for Layer II, and from 32 to 320 kbit/s for Layer III.

MPEG-2 BC (ISO/IEC 13818-3) provides

• a backwards compatible (BC) multichannel extension to MPEG-1; up to 5 main channels plus a 'low frequent enhancement' (LFE) channel can be coded; the bitrate range is extended up to about 1 Mbit/s;
• an extension of MPEG-1 towards lower sampling rates 16, 22.05, and 24 kHz for bitrates from 32 to 256 kbit/s (Layer I) and from 8 to 160 kbit/s (Layer II & Layer III).

MPEG-2 AAC (ISO/IEC 13818-7) provides

• a very high-quality audio coding standard for 1 to 48 channels at sampling rates of 8 to 96 kHz, with multichannel, multilingual, and multiprogram capabilities. AAC works at bitrates from 8 kbit/s for a monophonic speech signal up to in excess of 160 kbit/s/channel for very-high-quality coding that permits multiple encode/decode cycles. Three profiles of AAC provide varying levels of complexity and scalability.

MPEG-4 (ISO/IEC 14496-3) provides

• coding and composition of natural and synthetic audio objects,
• scalability of the bitrate of an audio bitstream,
• scalability of encoder or decoder complexity,
• Structured Audio: A universal language for score-driven sound synthesis,
• TTSI: An interface for text-to-speech conversion systems.

MPEG-7 (ISO/IEC 15938) will provide

• standardized descriptions and description schemes of audio structures and sound content,
• a language to specify such descriptions and description schemes.

Where can I find more information on the WEB?

There are some interesting sites where you can find more MPEG-Audio related informations:

• http://www.tnt.uni-hannover.de/project/mpeg/audio/
• http://www.sv.philips.com/mpeg/
• http://www.iis.fhg.de/amm/
• ftp://ftp.fhg.de/pub/layer3/
• http://www.mpeg.org/

Who can I contact if I have more questions?

There is a contact address to answer questions that you may have and that are not answered in this FAQ, in the standard, or the literature.
E-mail to: mpegaudio@tnt.uni-hannover.de

Where can I obtain copies of the MPEG Standards?

Copies of the MPEG standards can be obtained from the ISO secretariat or your National Standardisation Body. The address of the ISO secretariat is:

ISO/IEC Copyright Office
Case Postale 56
CH-1211 Genèva 20
Switzerland

URL: http://www.iso.ch/

How to join MPEG?

All experts all over the world who are working in the field of audio visual representation can join MPEG. First, you have to contact your National Standardisation Body which has to be a member of ISO/IEC JTC1. For each meeting of MPEG, you have to be on the accreditation list of your National Standardisation Body which has to forward this list to the ISO secretariat in advance of the meeting. In addition you have to sign up for each MPEG meeting a registration form and send it to the Convenor of MPEG. MPEG usually meets four times a year.

The address of the Convenor is:

Dr. Leonardo Chiariglione
Convenor WG11
Multimedia and Video Services
CSELT
Via G. Reiss Romoli, 274
I-10148 Torino
Italy

Tel: +39 11 228 6120/6116/5111
Fax: +39 11 228 6299/6190/5520
EMail: leonardo.chiariglione@cselt.it
URL: http://www.cselt.it/ufv/leonardo/