>Hi .... We are developing a nonuniform frequency sampling FIR digitalfilter (lowpass) with linear phase using Matlab5.3 and DSP toolbox (I dont remember the version of the DSP), however, We have arrived to a stuck point in the code becouse i am not very pro in Matlab. We have developed a uniform frequency sampling succefuly as follows: >%Consider the lowpass filter specifications as follows: > >% wp= 0.2 pi, Rp= 0.25 dB > >% ws= 0.3 pi, As= 50 dB Which means that Rs=0.00316 dB > >%Design an FIR filter using the frequency sampling approach. >% > >% (a) 20 samples to have value 1 at 0.2*pi and value 0 at 0.3*pi > >% >%Length of the FIR filter > >N = 20; >M = (N-1)/2; >Hrs = [1,1,1,zeros(1,15),1,1]; >%Samplimg Points in both Passband and stopband areas > >k1 = 0:floor((N-1)/2); > >k2 = floor((N-1)/2)+1:N-1; >angH = [-M*(2*pi)/N*k1, M*(2*pi)/N*(N-k2)]; >H = Hrs.*exp(j*angH); > >h = real(ifft(H,N)); >[Hr,ww,a,L] = Hr_Type2(h); >plot(ww/pi,Hr); > >axis([0,1,-0.2,1.2]); > >title('Amplitude Response of Uniform Frequency Sampling Method') > >xlabel('frequency in pi units') > >ylabel('Hr(w)') > >grid > >/*****the function used here Hr_Type2(h); is as: > >%%Linear-phase FIR filter: Symmetrical impulse response M even > > >function [Hr,w,b,L] = Hr_Type2(h); > >% Computes Amplitude response of Type-2 LP FIR filter > >% --------------- > >% [Hr,w,b,L] = Hr_Type2(h) > >% Hr = Amplitude Response > >% w = frequencies between [0 pi] over which Hr is computed > >% b = Type-2 LP filter coefficients > >% L = Order of Hr > >% h = Type-2 LP impulse response > >% > >M = length(h); > >L = M/2; > >b = 2*[h(L:-1:1)]; > >n = [1:1:L]; n = n-0.5; > >w = [0:1:500]'*pi/500; > >Hr = cos(w*n)*b'; >*********** > >so if you can help me to do the same with the nonuniform method i will be grateful > >or even if you can redirect me to a useful URL site which used to do the help.. > > >. > >Thanks... > >Emhmemmed _________________________________________________________________________ Get Your Private, Free E-mail from MSN Hotmail at http://www.hotmail.com. |