Subband Transforms

Abstract

Transforms that decompose the source into non-overlap** and contiguous frequency ranges called subbands are called subband transforms. A wavelet transform, as we shall see, is just a particular kind of subband transform. The source sequence is fed to a bank of bandpass filters which are contiguous and cover the full frequency range. The set of output signals are the subband signals and can be recombined without degradation to produce the original signal. For the sake of illustration, we start with ideal “brick-wall” filters in their frequency ranges. We develop the subband rate allocation formulas and calculate coding gain using both ideal and the realizable Haar filters.