代码:
%% ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ %% Output Info about this m-file fprintf(' *********************************************************** '); fprintf(' <DSP using MATLAB> Problem 7.13 '); banner(); %% ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ % bandstop wp1 = 0.25*pi; ws1 = 0.35*pi; ws2=0.65*pi; wp2=0.75*pi; delta1 = 0.025; delta2 = 0.005; tr_width = min(ws1-wp1, wp2-ws2); f = [wp1, ws1, ws2, wp2]/pi; [Rp, As] = delta2db(delta1, delta2) M = ceil((As-7.95)/(2.285*tr_width)) + 1; % Kaiser Window if As > 21 || As < 50 beta = 0.5842*(As-21)^0.4 + 0.07886*(As-21); else beta = 0.1102*(As-8.7); end fprintf(' Kaiser Window method, Filter Length: M = %d. beta = %.4f ', M, beta); n = [0:1:M-1]; wc1 = (ws1+wp1)/2; wc2 = (ws2+wp2)/2; %wc = (ws + wp)/2, % ideal LPF cutoff frequency hd = ideal_lp(wc1, M) + ideal_lp(pi, M) - ideal_lp(wc2, M); w_kai = (kaiser(M, beta))'; h = hd .* w_kai; [db, mag, pha, grd, w] = freqz_m(h, [1]); delta_w = 2*pi/1000; [Hr,ww,P,L] = ampl_res(h); Rp = -(min(db(1 :1: floor(wp1/delta_w)+1))); % Actual Passband Ripple fprintf(' Actual Passband Ripple is %.4f dB. ', Rp); As = -round(max(db(ws1/delta_w+1 : 1 : ws2/delta_w ))); % Min Stopband attenuation fprintf(' Min Stopband attenuation is %.4f dB. ', As); [delta1, delta2] = db2delta(Rp, As) %% ---------------------------------- %% Increse M %% ---------------------------------- M = M+2 hd = ideal_lp(wc1, M) + ideal_lp(pi, M) - ideal_lp(wc2, M); w_kai = (kaiser(M, beta))'; h = hd .* w_kai; [db, mag, pha, grd, w] = freqz_m(h, [1]); delta_w = 2*pi/1000; [Hr,ww,P,L] = ampl_res(h); Rp = -(min(db(1 :1: floor(wp1/delta_w)+1))); % Actual Passband Ripple fprintf(' Actual Passband Ripple is %.4f dB. ', Rp); As = -round(max(db(ws1/delta_w+1 : 1 : ws2/delta_w ))); % Min Stopband attenuation fprintf(' Min Stopband attenuation is %.4f dB. ', As); [delta1, delta2] = db2delta(Rp, As) n = [0:1:M-1]; % Plot figure('NumberTitle', 'off', 'Name', 'Problem 7.13 ideal_lp Method') set(gcf,'Color','white'); subplot(2,2,1); stem(n, hd); axis([0 M-1 -0.2 0.6]); grid on; xlabel('n'); ylabel('hd(n)'); title('Ideal Impulse Response'); subplot(2,2,2); stem(n, w_kai); axis([0 M-1 0 1.1]); grid on; xlabel('n'); ylabel('w(n)'); title('Kaiser Window'); subplot(2,2,3); stem(n, h); axis([0 M-1 -0.2 0.6]); grid on; xlabel('n'); ylabel('h(n)'); title('Actual Impulse Response'); subplot(2,2,4); plot(w/pi, db); axis([0 1 -100 10]); grid on; set(gca,'YTickMode','manual','YTick',[-90,-49,0]); set(gca,'YTickLabelMode','manual','YTickLabel',['90';'49';' 0']); set(gca,'XTickMode','manual','XTick',[0,f,1]); xlabel('frequency in pi units'); ylabel('Decibels'); title('Magnitude Response in dB'); figure('NumberTitle', 'off', 'Name', 'Problem 7.13 h(n) ideal_lp Method') set(gcf,'Color','white'); subplot(2,2,1); plot(w/pi, db); grid on; axis([0 2 -100 10]); xlabel('frequency in pi units'); ylabel('Decibels'); title('Magnitude Response in dB'); set(gca,'YTickMode','manual','YTick',[-90,-49,0]) set(gca,'YTickLabelMode','manual','YTickLabel',['90';'49';' 0']); set(gca,'XTickMode','manual','XTick',[0,f,1+f,2]); subplot(2,2,3); plot(w/pi, mag); grid on; %axis([0 2 -100 10]); xlabel('frequency in pi units'); ylabel('Absolute'); title('Magnitude Response in absolute'); set(gca,'XTickMode','manual','XTick',[0,f,1+f,2]); set(gca,'YTickMode','manual','YTick',[0.0,0.5,1.0]) subplot(2,2,2); plot(w/pi, pha); grid on; %axis([0 1 -100 10]); xlabel('frequency in pi units'); ylabel('Rad'); title('Phase Response in Radians'); subplot(2,2,4); plot(w/pi, grd*pi/180); grid on; %axis([0 1 -100 10]); xlabel('frequency in pi units'); ylabel('Rad'); title('Group Delay'); figure('NumberTitle', 'off', 'Name', 'Problem 7.13 h(n)') set(gcf,'Color','white'); plot(ww/pi, Hr); grid on; %axis([0 1 -100 10]); xlabel('frequency in pi units'); ylabel('Hr'); title('Amplitude Response'); set(gca,'YTickMode','manual','YTick',[-delta2,0,delta2,1 - delta1,1, 1 + delta1]) %set(gca,'YTickLabelMode','manual','YTickLabel',['90';'45';' 0']); set(gca,'XTickMode','manual','XTick',[0,f,2]); %% +++++++++++++++++++++++++++++++++++++++++ %% fir1 function method %% +++++++++++++++++++++++++++++++++++++++++ f = [wp1, ws1, ws2, wp2]/pi; m = [1 0 1]; ripple = [0.025 0.005 0.025]; [N, wc, beta, ftype] = kaiserord(f,m,ripple); fprintf(' ------------ kaiserord function: START--------------- '); fprintf(' --------- results used by fir1 function --------- '); N wc beta ftype fprintf('------------- kaiserord function: FINISH--------------- '); %h_check = fir1(M-1, [wc1 wc2]/pi, 'stop', window(@kaiser, M)); %h_check = fir1(N, wc, ftype, window(@kaiser, N+1)); h_check = fir1(N, wc, ftype, kaiser(N+1, beta)); [db, mag, pha, grd, w] = freqz_m(h_check, [1]); [Hr,ww,P,L] = ampl_res(h_check); Rp = -(min(db(1 :1: floor(wp1/delta_w)+1))); % Actual Passband Ripple fprintf(' Actual Passband Ripple is %.4f dB. ', Rp); As = -round(max(db(ws1/delta_w+1 : 1 : ws2/delta_w ))); % Min Stopband attenuation fprintf(' Min Stopband attenuation is %.4f dB. ', As); %% ---------------------------------- %% Increse N %% ---------------------------------- N = N+2 h_check = fir1(N, wc, ftype, kaiser(N+1, beta)); [db, mag, pha, grd, w] = freqz_m(h_check, [1]); [Hr,ww,P,L] = ampl_res(h_check); As = -round(max(db(ws1/delta_w+1 : 1 : ws2/delta_w ))); % Min Stopband attenuation fprintf(' Min Stopband attenuation is %.4f dB. ', As); figure('NumberTitle', 'off', 'Name', 'Problem 7.13 fir1 Method') set(gcf,'Color','white'); subplot(2,2,1); stem(n, hd); axis([0 M-1 -0.2 0.6]); grid on; xlabel('n'); ylabel('hd(n)'); title('Ideal Impulse Response'); subplot(2,2,2); stem(n, w_kai); axis([0 M-1 0 1.1]); grid on; xlabel('n'); ylabel('w(n)'); title('Kaiser Window'); subplot(2,2,3); stem([0:N], h_check); axis([0 M -0.2 0.7]); grid on; xlabel('n'); ylabel('h\_check(n)'); title('Actual Impulse Response'); subplot(2,2,4); plot(w/pi, db); axis([0 1 -100 10]); grid on; set(gca,'YTickMode','manual','YTick',[-90,-49,0]) set(gca,'YTickLabelMode','manual','YTickLabel',['90';'49';' 0']); set(gca,'XTickMode','manual','XTick',[0,f,1]); xlabel('frequency in pi units'); ylabel('Decibels'); title('Magnitude Response in dB'); figure('NumberTitle', 'off', 'Name', 'Problem 7.13 h(n) fir1 Method') set(gcf,'Color','white'); subplot(2,2,1); plot(w/pi, db); grid on; axis([0 2 -100 10]); xlabel('frequency in pi units'); ylabel('Decibels'); title('Magnitude Response in dB'); set(gca,'YTickMode','manual','YTick',[-90,-49,0]) set(gca,'YTickLabelMode','manual','YTickLabel',['90';'49';' 0']); set(gca,'XTickMode','manual','XTick',[0,f,1+f,2]); subplot(2,2,3); plot(w/pi, mag); grid on; %axis([0 1 -100 10]); xlabel('frequency in pi units'); ylabel('Absolute'); title('Magnitude Response in absolute'); set(gca,'XTickMode','manual','XTick',[0,f,1+f,2]); set(gca,'YTickMode','manual','YTick',[0.0,0.5,1.0]) subplot(2,2,2); plot(w/pi, pha); grid on; %axis([0 1 -100 10]); xlabel('frequency in pi units'); ylabel('Rad'); title('Phase Response in Radians'); subplot(2,2,4); plot(w/pi, grd*pi/180); grid on; %axis([0 1 -100 10]); xlabel('frequency in pi units'); ylabel('Rad'); title('Group Delay');
运行结果:
最小阻带衰减设计是46.2351dB,kaiser窗长度M=57时满足要求。
利用Kaiser窗得到的脉冲响应,计算其幅度响应(dB和Absolute单位)、相位响应和群延迟响应。
振幅响应
通带部分
阻带部分
利用fir1函数得到脉冲响应,和前面进行对比
两种方法,区别不大。