Spectral sound equalization is one of the most important methods for processing audio signals. Equalizers are found in various forms in the transmission of audio signals from a sound studio to the listener. The more complex filter functions are used in sound studios. But in almost every consumer product like car radios, hifi amplifiers, simple filter functions are used for sound equalization. We first discuss basic filter types followed by the design and implementation of recursive audio filters. In Sections 5.3 and 5.4 linear phase nonrecursive filter structures and their implementation are introduced.
For filtering of audio signals the following filter types are used:
Band-pass filters with a constant relative bandwidth fb/fc are very important for audio applications [Cre03]. The bandwidth is proportional to the center frequency, which is given by (see Fig. 5.2).