《DSP using MATLAB》示例 Example 9.8

Posted 2020-09-20 沧海一粟

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。