fig6_12.m

数字信号处理Matlab演示文件,其中各个文件加放置了不同的matlab子文件

echo on
% fig 6-12:
% (a) with remez exchange algorithm (order 20)
% (b) 31 coefficients (order 31) FIR filter with Hanning window
% (c) Comparison of two designs showing passband/stopband
echo off

nr = 19; % coefficient sizes (-1) for remez/Hanning
nf = 30;

% Note: the quoted cutoffs have been manupulated to get
% -3dB cutoffs occuring at actual frequency wn=0.1 (in
% Matlab wn = 1 is at 0.5*ws hence wn = 0.2 or thereabouts
% is used here) - you'll see this in Figure 3

f = [0 0.11 0.36 1.0]; % Remez specification
mag = [100 100 0 0];


wn = 0.23;	    % Hanning window cutoff

% First process remez design

b = remez(nr,f,mag);
[h,w] = freqz(b,1,256);
m = 20*log10(abs(h));
figure(1)
plot(w/pi/2,m-40,'b');
xlabel('normalised frequency')
ylabel('gain (dB)')
axis([0 0.5 -100 20]);
pause;

% Hanning window design

b1 = fir1(nf,wn,hanning(nf+1));
[h1,w1] = freqz(b1,1,256);
mag1 = 20*log10(abs(h1));
f1 = w1/2/pi;
figure(2)
plot(f1,mag1,'b');
xlabel('normalised frequency')
ylabel('gain (dB)')
axis([0 0.5 -100 20]);
pause;

% finally compare two designs
% green line shows -3dB cutoff
% magenta line defines passband/stopband

figure(3)
f2 = [0 0.1 0.1 0.18 0.18 0.5];
mag2 = [0 0 -100 -100 -44 -44];
plot(f1,mag1,'r',w/pi/2,m-40,'b',w/pi/2,-3*ones(1,256),'g',f2,mag2,'m');
xlabel('normalised frequency')
ylabel('gain (dB)')
axis([0 0.5 -100 20]);
pause;