DEMO_FILTERBANKS CQT, ERBLET and AUDLET filterbanks
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.
Figure 1: ERBLET representations
The high-redundany plot (top) consists of 400 channels (~9 filters
per ERB) and low-redundany plot (bottom) consists of 44 channels
(1 filter per ERB).
Figure 2: CQT representations
Both representations consist of 280 channels (32 channels per octave,
frequency range 50Hz-20kHz). The high-redundany represention is on
the top and the low-redundancy repr. is on the bottom.
Figure 3: AUDLET representations
The first representation consists of 72 channels BARKlet FB (3 filters
per Bark in the frequency range 100Hz-16kHz using fractional subsampling.
The second representation consists of 40 channels MELlet FB using
uniform subsampling and triangular windows.
Url: http://ltfat.github.io/doc/demos/demo_filterbanks.html
See also: audfilters, erbfilters, cqtfilters.
Package: ltfat