《DSP using MATLAB》示例 Example 9.8

代码：

%% ------------------------------------------------------------------------
%%            Output Info about this m-file
fprintf('\n***********************************************************\n');
fprintf('        <DSP using MATLAB> Exameple 9.8 \n\n');

time_stamp = datestr(now, 31);
[wkd1, wkd2] = weekday(today, 'long');
fprintf('      Now is %20s, and it is %7s  \n\n', time_stamp, wkd2);
%% ------------------------------------------------------------------------

I = 5; Rp = 0.1; As = 30; wp = pi/I; ws = wp+pi*0.12;
[delta1, delta2] = db2delta(Rp, As); weights = [delta2/delta1, 1];
F = [0, wp, ws, pi]/pi; A = [I, I, 0, 0];
h = firpm(30, F, A, weights); n = [0:length(h)-1];
[Hr, w, a, L] = Hr_Type1(h); Hr_min = min(Hr); w_min = find(Hr == Hr_min);
H = abs(freqz(h, 1, w)); Hdb = 20*log10(H/max(H)); min_attn = Hdb(w_min);

%% -----------------------------------------------------------------
%%                             Plot
%% -----------------------------------------------------------------
Hf1 = figure('units', 'inches', 'position', [1, 1, 8, 6], ...
	'paperunits', 'inches', 'paperposition', [0, 0, 6, 4], ...
	'NumberTitle', 'off', 'Name', 'Exameple 9.8');
set(gcf,'Color','white'); 

TF = 10;

subplot(2, 2, 1);
Hs1 = stem(n, h, 'filled'); set(Hs1, 'markersize', 2);
axis([-1, length(n), -0.5, 1.5]); grid on;
xlabel('n', 'vertical', 'bottom'); ylabel('Amplitude');
title('Impulse Response', 'fontsize', TF);

subplot(2, 2, 3);
plot(w/pi, Hr, 'm', 'linewidth', 1.0); axis([0, 1, -1, 6]); grid on;
xlabel('frequency in \pi units', 'fontsize', 10); ylabel('Amplitude');
title(' Amplitude Response ', 'fontsize', TF);
set(gca, 'xtick', [0, wp/pi, ws/pi, 1]);
set(gca, 'ytick', [0, I]);

subplot(2, 2, 2);
plot(w/pi, Hdb, 'm', 'linewidth', 1.0); axis([0, 1, -50, 10]); grid on;
xlabel('frequency in \pi units '); ylabel('Decibels');
title('Log-mag Response ', 'fontsize', TF);
set(gca, 'xtick', [0, wp/pi, ws/pi, 1]);
set(gca, 'ytick', [-50, round(min_attn), 0]);

subplot(2, 2, 4);
lw = length(w)-1; PB = [0:floor(wp/pi*lw)]; HrPB = Hr(PB+1)-I;
SB = [ceil(ws/pi*lw):lw]; HrSB = Hr(SB+1);
[AX, H1, H2] = plotyy(PB/lw, HrPB, SB/lw, HrSB);

delta1 = round(delta1*I*100)/100; delta2 = round(delta2*I*100)/100;
set(AX(1), 'xtick', [0, wp/pi, ws/pi, 1]);
set(AX(1), 'ytick', [-delta1, 0, delta1], 'Ycolor', 'g');
set(AX(2), 'xtick', [0, wp/pi, ws/pi, 1]);
set(AX(2), 'ytick', [-delta2, 0, delta2], 'Ycolor', 'r');
set(H1, 'color', 'g', 'linewidth', 1);
set(H2, 'color', 'r', 'linewidth', 1);
title('scaled ripples', 'fontsize', TF);
xlabel('Frequency in \pi units');

　　运行结果：

尽管该滤波器通过了原始信号，如果信号是全频带π弧度的，那么邻近的谱能量可能发生泄漏。因此需要更好的设计指标，本节的后面有讨论。