MATLAB 回聲信號的產生與消除
%首先使長時間的FIR濾波器產生回聲。（產生房間的沖擊響應）
M = 4001;
fs = 8000;
[B,A] = cheby2(4,20,[0.1 0.7]);
Hd = dfilt.df2t([zeros(1,6) B],A);
hFVT = fvtool(Hd); % Analyze the filter
set(hFVT, 'Color', [1 1 1])
H = filter(Hd,log(0.99*rand(1,M)+0.01).*sign(randn(1,M)).*exp(-0.002*(1:M)));
H = H/norm(H)*4; % Room Impulse Response
plot(0:1/fs:0.5,H);
xlabel('Time [sec]');
ylabel('Amplitude');
title('Room Impulse Response');
set(gcf, 'Color', [1 1 1])
%然後讀取matlab裏面自帶的人聲，並且播放（不必緊張，這不是英語聽力）
load nearspeech
n = 1:length(v);
t = n/fs;
plot(t,v);
axis([0 33.5 -1 1]);
xlabel('Time [sec]');
ylabel('Amplitude');
title('Near-End Speech Signal');
set(gcf, 'Color', [1 1 1])
p8 = audioplayer(v,fs);
playblocking(p8);
The Far-End Speech Signal
%現在播放回聲：就是從喇叭發出，房間反彈，最後被麥克風接收到的聲音。這把聲音是通過我們上面設計的FIR濾波器產生的
load farspeech
x = x(1:length(x));
dhat = filter(H,1,x);
plot(t,dhat);
axis([0 33.5 -1 1]);
xlabel('Time [sec]');
ylabel('Amplitude');
title('Far-End Echoed Speech Signal');
set(gcf, 'Color', [1 1 1])
p8 = audioplayer(dhat,fs);
playblocking(p8);
%人聲和回聲加在壹起，麥克風接收到的實際聲音是：
d = dhat + v+0.001*randn(length(v),1);
plot(t,d);
axis([0 33.5 -1 1]);
xlabel('Time [sec]');
ylabel('Amplitude');
title('Microphone Signal');
set(gcf, 'Color', [1 1 1])
p8 = audioplayer(d,fs);
playblocking(p8);
%使用頻域自適應濾波器去除回聲
mu = 0.025;
W0 = zeros(1,2048);
del = 0.01;
lam = 0.98;
x = x(1:length(W0)*floor(length(x)/length(W0)));
d = d(1:length(W0)*floor(length(d)/length(W0)));
% Construct the Frequency-Domain Adaptive Filter
hFDAF = adaptfilt.fdaf(2048,mu,1,del,lam);
[y,e] = filter(hFDAF,x,d);
n = 1:length(e);
t = n/fs;
pos = get(gcf,'Position');
set(gcf,'Position',[pos(1), pos(2)-100,pos(3),(pos(4)+85)])
subplot(3,1,1);
plot(t,v(n),'g');
axis([0 33.5 -1 1]);
ylabel('Amplitude');
title('Near-End Speech Signal');
subplot(3,1,2);
plot(t,d(n),'b');
axis([0 33.5 -1 1]);
ylabel('Amplitude');
title('Microphone Signal');
subplot(3,1,3);
plot(t,e(n),'r');
axis([0 33.5 -1 1]);
xlabel('Time [sec]');
ylabel('Amplitude');
title('Output of Acoustic Echo Canceller');
set(gcf, 'Color', [1 1 1])
p8 = audioplayer(e/max(abs(e)),fs);
playblocking(p8);
%凳凳凳凳，大功告成
%回聲的產生方法很多，還有壹種鏡像法，模擬聲音在壹個六面體房間內墻面的每次反彈。澳洲某個大學的哥們的個人主頁上有程序，有興趣可以找找。