《DSP using MATLAB》 示例 Example 9.16

Posted 2020-09-20 沧海一粟

代码：

%% ------------------------------------------------------------------------
%%            Output Info about this m-file
fprintf(\'\\n***********************************************************\\n\');
fprintf(\'        <DSP using MATLAB> Exameple 9.16 \\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);
%% ------------------------------------------------------------------------

% Given Parameters:
I = 4; D = 3; Rp = 0.1; As = 40; 
wxp = 0.8*pi; wxs1 = 0.9*pi; wxs2 = 0.7*pi;

% Computed Filter Parameters
wp = wxp/I; ws = min((2*pi/I-wxs1/I), (2*pi/D-wxs2/I));    

% Filter Design:
[delta1, delta2] = db2delta(Rp, As); 

[N, F, A, weights] = firpmord([wp, ws]/pi, [1, 0], [delta1, delta2], 2); 
N = ceil(N/2)*2 + 1;
N
F
A
weights

h = firpm(N, F, I*A, weights); 
%delay = N/2;                        % delay imparted by the filter  
% n = [0:length(h)-1];
[Hr, w, a, L] = Ampl_res(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 9.16\');
set(gcf,\'Color\',\'white\'); 

TF = 10;

subplot(2, 1, 1); 
plot(w/pi, Hr, \'m\', \'linewidth\', 1.0); axis([0, 1, -0.1, I+0.4]); grid on;
xlabel(\'Frequency in \\pi units\', \'vertical\', \'middle\'); ylabel(\'Amplitude\', \'vertical\', \'middle\'); 
title(\'Amplitude Response \', \'fontsize\', TF, \'vertical\', \'baseline\');
set(gca, \'xtick\', [0, wp/pi, ws/pi, 1]); 
set(gca, \'ytick\', [0, I]);


subplot(2, 1, 2); 
plot(w/pi, Hdb, \'m\', \'linewidth\', 1.0); axis([0, 1, -60, 10]); grid on;
xlabel(\'Frequency in \\pi units\', \'fontsize\', TF, \'vertical\', \'middle\');
ylabel(\'Decibels\', \'vertical\', \'cap\');
title(\'Log-magnitude Response\', \'fontsize\', TF, \'vertical\', \'baseline\');
set(gca, \'xtick\', [0, wp/pi, ws/pi, 1], \'ytick\', [-60, round(min_attn), 0]);

　　运行结果：

        衰减达到40dB。

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               第9章结束。

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