filter.m

用于语音识别语音增强方面的matlab工具包

function [y,zf] = filter(b,a,X,varargin)
% FILTER One-dimensional digital filter.
%    Y = FILTER(B,A,X) filters the data in vector X with the
%    filter described by vectors A and B to create the filtered
%    data Y.
%
%    Y = FILTER(B,A,X,'noncausal') performs noncausal filtering,
%    i.e. the time information is shifted to match the group delay
%    of the filter.
%
%    Y = FILTER(B,A,X,'causal') performs causal filtering (default),
%
%    Y = FILTER(B,A,X,'backwards') performs filtering on the time reversed
%    signal, i.e. it flips the signal backwards before filtering and flips
%    the filtered signal to obtain original time orientation

% $Id: filter.m 112 2006-03-22 15:14:07Z bassus $

causal = 1;
backw = 0;
while length(varargin)
    if (strcmp(varargin{1},'noncausal') ...
            || strcmp(varargin{1},'nc'))
        causal=0;
        varargin=varargin(2:end);
    elseif (strcmp(varargin{1},'causal'))
        causal=1;
        varargin=varargin(2:end);
    elseif strcmp(varargin{1},'backwards')
        % reverse time
        backw = 1;
        X.s = flipud(X.s(:));
        varargin=varargin(2:end);
    end
end

[y_,zf] = filter(b,a,X.s,varargin{1:end});

% set time vector

tobj = X.time;
if causal
  t = tobj;
else
  grpdel_ = grpdelay(b,a);
  grpdel  = grpdel_(abs(grpdel_)~=Inf);
  t = tobj-mean(grpdel)/tobj.fs;
end
y = signal(y_,t);

% set region of validity

y.valid = X.valid;
y.valid(1) = X.valid(1)+limpz(b,a);

% turn back time
if backw
    y.s = flipud(y.s(:))';
end