gusucode.com > 信号处理工具箱 - signal源码程序 > signal\signal\signal\private\bandpass.m
function [DH,DW] = bandpass(N, F, GF, W, delay) %BANDPASS Desired frequency response for bandpass filters. % CREMEZ(N,F,'bandpass', ...) designs a linear-phase bandpass filter % response using CREMEZ. % % CREMEZ(N,F,{'bandpass', D}, ...) specifies group-delay offset D such % that the filter response will have a group delay of N/2 + D in % units of the sample interval, where N is the filter order. % Negative values create less delay, while positive values create % more delay. By default, D=0. % % The symmetry option SYM defaults to 'even' if unspecified in the % call to CREMEZ, if no negative band edge frequencies are % specified in F. % % EXAMPLE: Design a 31-tap, complex bandpass filter % b = cremez(30,[-1 -.5 -.4 .7 .8 1],'bandpass'); % freqz(b,1,512,'whole'); % % EXAMPLE: Reduced group delay filter response: % b = cremez(30,[0 .6 .7 1],{'bandpass',-1}); % % See also CREMEZ. % Authors: L. Karam, J. McClellan % Revised: October 1996, D. Orofino % % Copyright (c) 1988-98 by The MathWorks, Inc. % $Revision: 1.1 $ $Date: 1998/06/03 16:14:35 $ % [DH,DW]=BANDPASS(N,F,GF,W,DELAY) % N: filter order (length minus one) % F: vector of band edges % GF: vector of frequencies at which to evaluate % W: vector of weights, one per band % DELAY: negative slope of the phase. % M/2=(L-1)/2 for exact linear phase. % % DH: vector of desired filter response (mag & phase) % DW: vector of weights (positive) % % NOTE: DH(f) and DW(f) are specified as functions of frequency % Support query by CREMEZ for the default symmetry option: if nargin==2, % Return symmetry default - pass call off to multiband: if length(F)>4, F(6)=F(5); end; F(5)={[]}; % Construct dummy mags vector DH=multiband(N,F); return end % Standard call: error(nargchk(4,5,nargin)); if nargin<5, delay = 0; end % multiband will adjust for linear phase Le = length(F); mags = [1;1] * rem(0:Le/2-1, 2); mags = mags(:); jkl = find( F(1:Le-1).*F(2:Le) <= 0 ); if rem(jkl(1)-1,4), mags = 1-mags; end [DH,DW] = multiband(N, F, GF, W, mags, delay); % end of bandpass.m