A modulated filterbank
is composed of analysis branches which:
-
Modulate the input to center the desired sub-band at DC
-
Lowpass filter the modulated signal to isolate the
desired sub-band
-
Downsample the lowpass signal
The synthesis branches interpolate the sub-band signals by
upsampling and lowpass filtering, then modulate each sub-band
back to its original spectral location (see
Figure 1).
In MM-branch critically-sampled
uniformly-modulated filterbanks, the
kkth branch has a modulation
frequency of
±
ω
k
=2πMkradians
±
ω
k
2
M
k
radians
, a lowpass cutoff frequency of
πM
M
radians, and a downsampling/upsampling factor of
MM.
The most common way to implement this type of uniform modulated
filterbank is through the use of polyphase filterbanks and DFTs.