Distortion free filter bank for a hearing device

The application relates to a filter bank for an audio processing device, e.g. a hearing aid. The filter bank comprises €¢ an analysis filter bank comprising a plurality of M first filters h m (n), where m=0, 1, ..., M-1 is a frequency band index, and whose impulse responses are modulated from a first linear phase prototype filter h(n) with a first predetermined modulation sequence ms1, n being a time index, the first prototype filter h(n) having a first filter length of L h ; €¢ a synthesis filter bank comprising a plurality of M second filters g m (n), m=0, 1, ..., M-1, whose impulse responses are modulated from a second linear phase prototype filter g(n) with a second predetermined modulation sequence ms2, the second prototype filter g(n) having a second filter length of Lg; €¢ the plurality of first and second filters being arranged in pairs, each pair forming a frequency channel. €¢ the first modulation sequence is a complex or real function of time n, frequency band index m, and a first prototype filter delay Ä h , €¢ the second modulation sequence is a complex or real function of time n, frequency band index m, and a second prototype filter delay Ä g , €¢ the first filter length L h and the second filter length Lg are both uneven, and €¢ the first prototype filter delay Ä h is equal to (L h -1)/2 and second prototype filter delay Ä g , is equal to (L g -1)/2, and the first and second prototype filter delay Ä h and Ä g , are constants of the analysis filter bank and the synthesis filter bank, respectively.