Function: wfilt_db
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.
    
    

Url: http://ltfat.github.io/doc/wavelets/wfilt_db.html

Package: ltfat