Communication Acoustics: An Introduction to Speech, Audio and Psychoacoustics

15Time–Frequency-domain Processing and Coding of Audio

A common trend in the field of audio is to process the audio signal in the time–frequency domain. In other words, the input audio signal is divided into a number of frequency bands which are processed separately and also depending on time. The aim in such processing is, for example, data compression, audio effects, or the enhancement of audio quality. The benefit of time–frequency processing in such tasks is that the structure of human hearing mechanisms is based on similar time–frequency analysis of the ear canal signals. Already many applications, such as the perceptual coding of audio, take advantage of the human hearing resolution in the time–frequency domain. An emerging field is multi-channel and spatial applications utilizing time–frequency processing.

15.1 Basic Techniques and Concepts for Time–Frequency Processing

The use of time–frequency transforms to visualize audio signals was already touched on in Section 3.2.6 on page 53. This chapter elaborates on the techniques and introduces some phenomena, concepts, and issues related to the processing of audio in the time–frequency domain. We will describe the time–frequency processing methods first using the concepts of frame-based analysis, and second using the concepts of downsampled filter banks.

5.1.1 Frame-Based Processing

Many time–frequency-domain audio techniques are implemented such that an input signal(s) is first divided into overlapping time frames, after ...