To provide a new method and apparatus for the improvement of digital filter banks by a complex expansion of cosine modulated digital filter banks.

The present invention employs complex-exponential modulation of a low-pass prototype filter and a new method for optimizing the characteristics of this filter. The present invention substantially reduces artifacts, due to aliasing emerging from independent modifications of subband signals, for example when using a filter bank as a spectral equalizer and is preferably realized by software, running on a standard PC or a digital signal processor, but can also be hardcoded on a custom chip. The invention is essentially for improving the various types of digital equalizers, adaptive filters, multiband companders and spectral envelope adjusting filter banks used in high-frequency reconstruction systems.