Digital Audio Signal Processing, Second Edition

Chapter 9

Audio Coding

For transmission and storage of audio signals, different methods for compressing data have been investigated besides the pulse code modulation representation. The requirements of different applications have led to a variety of audio coding methods which have become international standards. In this chapter basic principles of audio coding are introduced and the most important audio coding standards discussed. Audio coding can be divided into two types: lossless and lossy. Lossless audio coding is based on a statistical model of the signal amplitudes and coding of the audio signal (audio coder). The reconstruction of the audio signal at the receiver allows a lossless resynthesis of the signal amplitudes of the original audio signal (audio decoder). On the other hand, lossy audio coding makes use of a psychoacoustic model of human acoustic perception to quantize and code the audio signal. In this case only the acoustically relevant parts of the signal are coded and reconstructed at the receiver. The samples of the original audio signal are not exactly reconstructed. The objective of both audio coding methods is a data rate reduction or data compression for transmission or storage compared to the original PCM signal.

9.1 Lossless Audio Coding

Lossless audio coding is based on linear prediction followed by entropy coding [Jay84] as shown in Fig. 9.1:

• Linear Prediction. A quantized set of coefficients P for a block of M samples is determined which leads to an ...