Chapter 13: Basic Audio Compression Techniques

Sun Microsystems, Inc. has made available the code for its implementation on standards G.711, G.721, and G.723, in C. The code can be found here

Sample audio files are given there as well. Since the code operates on raw 2-byte data, the link also gives simple matlab conversion code to read and write .wav and .raw data. Internally, audio data is treated as float, in the range [-1..1]. So if we are operating on 8-bit samples, the conversion from external, byte, data to internal, float, data can be carried out by the operation

float = byte/128 - 1

This converts from the range [0..255] to the range [-1..1]. For 2-byte, 16-bit data, the conversion is

float = double - byte/256 - 1

International Telecommunication Union (ITU)

For audio, the court of final appeal is the ITU standards body itself: it is standards promoted by such groups that in fact allow our modems to talk to each other, mobile communications to be developed, and so on.

comp.speech Frequently Asked Questions

More information on speech coding may be found in the speech FAQ files.

Introduction to CELP Coding

Speex is based on CELP, which stands for Code Excited Linear Prediction.

LPC and CELP Codes

LPC and CELP codes can be found here.

Speech Coding

Speech coding is an application of data compression of digital audio signals containing speech.

Source Coding Basics and Speech Coding

A lecture note for speech coding.

Speech Coding Techniques

Speech coding is the process of transforming the speech signal in a more compressed form, which can then be transmitted with few numbers of binary digits ...