WFILT_DB Daubechies FIR filterbank
Usage: [h,g] = wfilt_db(N);
Input parameters:
N : Order of Daubechies filters.
Output parameters:
H : cell array of analysing filters impulse reponses
G : cell array of synthetizing filters impulse reponses
a : array of subsampling (or hop) factors accociated with
corresponding filters
[H,G] = dbfilt(N) computes a two-channel Daubechies FIR filterbank
from prototype maximum-phase analysing lowpass filter obtained by
spectral factorization of the Lagrange interpolator filter. N also
denotes the number of zeros at z=-1 of the lowpass filters of length
2N. The prototype lowpass filter has the following form (all roots of
R(z) are outside of the unit circle):
H_l(z)=(1+z^-1)^N*R(z),
where R(z) is a spectral factor of the Lagrange interpolator P(z)=2R(z)*R(z^{-1})
All subsequent filters of the two-channel filterbank are derived as
follows:
H_h(z)=H_l((-z)^-1)
G_l(z)=H_l(z^-1)
G_h(z)=-H_l(-z)
making them an orthogonal perfect-reconstruction QMF.
Examples:
---------
:
wfiltinfo('db8');
References:
I. Daubechies. Ten Lectures on Wavelets. Society for Industrial and
Applied Mathematics, Philadelphia, PA, USA, 1992.
Package: ltfat