Perceptual Audio Codecs

What to Listen For

Dear Reader,

Welcome to this educational package on audio coding artifacts, prepared by members of the AES Technical Committee on Coding of Audio Signals.

This is the second edition of the educational material originally presented by the AES Technical Council as an educational/tutorial CD-ROM in 2001, combining background information on perceptual audio coding with specific audio examples. To facilitate the use on many viewing devices, the content can be played back on both computers and mobile devices, such as tablets or mobile phones. We hope you find this a useful feature.

Compared to other "classic" disciplines in audio engineering, the field of perceptual audio coding is a rather comparably young technology, combining elements from digital signal processing, coding theory, and psychoacoustics into one system. It is, however, mostly the psychoacoustics that frequently leads to questions from non-experts ("how does that work?") and sometimes is even perceived as some kind of "black magic" within the coder. Since many of the members of the AES Technical Committee on Coding of Audio Signals have been confronted with such questions, the idea of an educational publication on this topic soon found broad support within the group once its concept was formulated. It was Markus Erne who originally proposed the production of a CD-ROM that would offer non-experts some guidance on the background and sound of the perceptual effects a listener is likely to be confronted with when working with compressed audio signals. Initiated at a Technical Committee meeting at the AES 106th Convention in Munich in 1999, the idea eventually took more than two years and quite a number of Technical Committee meetings to be fully developed and implemented within the committee, finally leading to this publication. After successful sale of several print generations of the original CD ROMs by the AES, the Technical Committee on Audio Coding felt that it was time for an update to include new coding strategies that have become popular since the first generation CD ROM release. This second-generation material features a number of enhancements that the Technical Committee felt were useful and timely to increase its attractivity:

  • New material on advanced coding strategies has been added, partially with exciting interactive displays. Some of the graphics of the original material were enhanced in the same way.
  • Audio playback is now seamless and convenient (without external player applications) due to the use of HTML5’s audio capabilities.
  • The material was provided as a download package (rather than a hybrid CD ROM) and formatted to seamlessly display on modern reproduction devices, such as computers, tablets and mobile phones.

Of course, such projects do not happen all by themselves. They are the fruit of hard behind-the-scenes work by motivated individuals. First of all we acknowledge the outstanding contributions of Dr. Markus Erne who inspired us and drove the first generation of this project to its completion. He spent many hours coordinating the contributions, setting up the electronic infrastructure and, finally, assembling the CD-ROM master. For the second edition we want to express our special thanks to Sascha Dick who was of invaluable help in driving the extension activities. Our thanks also go to all the authoring Technical Committee members whose contributions facilitated the success of the project by preparing and reviewing both the tutorial chapters and its accompanying audio excerpts. We would also like to extend our thanks to all the AES officials who have been vital in making things happen, including the officers of the AES Technical Council and the staff of the AES publications office. Furthermore the generous support of the Fraunhofer Institute for Integrated Circuits (IIS) for the conversion of the existing material to the new web format is acknowledged. Finally, thanks go to the European Broadcasting Union (EBU) and David Wood, who kindly gave permission for the use of some audio excerpts from EBU's legendary "SQAM" (Sound Quality Assessment Material) recording.

We hope that you will find this material a valuable resource for education and listener training and that it may contribute widely to the knowledge of the interested community.

Jürgen Herre and Schuyler Quackenbush, cochairs
AES Technical Committee on Coding of Audio Signals
October 2022

Version 2.1