This demo shows CQT (Constant Quality Transform), ERBLET (Equivalent Rectangular Bandwidth -let transform), and AUDLET (Auditory -let) representations acting as filterbanks with high and low redundancies. Note that ERBLET and AUDLET are similar concepts. The main difference is that ERBlet uses only the perceptual ERB scale while AUDlet allows for various perceptual scales like Bark or Mel scales. In short, ERBFILTERS is a wrapper of AUDFILTERS for the ERB scale. Filterbanks are build such that the painless condition is always satisfied. Real input signal and filters covering only the positive frequency range are used. The redundancy is calculated as a ratio of the number of (complex) coefficients and the input length times two to account for the storage requirements of complex numbers.
- The high redundancy representation uses 'uniform' subsampling i.e. all channels are subsampled with the same subsampling factor which is the lowest from the filters according to the painless condition rounded towards zero.
- The low redundancy representation uses 'fractional' subsampling which results in the least redundant representation still satisfying the painless condition. Actual time positions of atoms can be non-integer, hence the word fractional.