3.3 Drawbacks of classical filterbank designs

To begin with, the reference to "classical" filterbank designs, generally refers to the filterbank types that youshould have seen up to now. These include the following types, that can be reviewed if necessary:

• Uniform Modulated Filterbanks
• Polyphase/DFT Implementation of Uniform Modulated Filterbanks

Drawbacks to classical implementation

The classical filterbanks that we have considered so far (those listed above) give perfect reconstruction performanceonly when the analysis and synthesis filters are ideal. With non-ideal ( i.e. , implementable) filters, aliasing will result from the downsampling/upsamplingoperation and corrupt the output signal. Since aliasing distortion is inherently non-linear, it may be veryundesirable in certain applications. Thus, long analysis/synthesis filters might be required to force aliasingdistortion down to tolerable levels. The cost of long filters is somewhat offset by the efficient polyphase implementation,though.

That said, clever fliter designs have been proposed which prevent aliasing in neighboring sub-bands. These designs include the following references: Rothweiler , Crochiere and Rabiner , and Vaidyanathan . As neighboring-subband aliasing typically constitutes the bulk ofaliasing distortion, these designs give significant performance gains. In fact, such filter designs are used inMPEG high-performance audio compression standards.