窗函数法设计低通滤波器资料

附录

[s, fs,bits]=wavread('d:\yyxinhao.wav');

ss=s(:,1);

% sound(s,fs,bits)

s1=s(17000:end);

figure(1);

subplot(311)

plot(ss)

title('语音信号')

subplot(312)

plot(s1)

title('截短语音信号');

wavwrite(s1,fs,'s1.wav');

S1=fft(s1);

subplot(313);

plot(s1);

title('截短预处理语音信号')

figure(2)

subplot(221)

plot(abs(S1))

title('语音信号频谱图');

N=length(s);

fn=10^5;

t=0:1/fs:(N-1)/fs;

s2=ss'+0.22*sin(fn*2*pi*t);

wavwrite(s2,fs,'s2.wav');

subplot(222)

plot(abs(S1))

title('预处理语音信号频谱'); wavwrite(s2,fs,'s2.wav');

subplot(223);

S2=fft(s2);

plot(abs(S2));

title('加噪后语音信号频谱图');

%sound(ss2,fs,bits)

wp=.2*pi;

wst=.3*pi;

wc=(wp+wst)/2;

N=ceil(3.1*2*pi/(wst-wp));

r=(N-1)/2;

hn1=fir1(N-1,wc/pi,'low',hanning(N)); hd=ideal_hp1(wc,N);

w_han=(hanning(N))';

h=hd.*w_han;

figure(3)

subplot(211)

stem(n,hd)

title('理想单位脉冲响应hd(n)'); subplot(212)

stem(n,h);

title('实际单位脉冲响应hd(n)');

s3=conv(s2,hn1);

wavwrite(s3,fs,'s3.wav');

sound(s3,fs,bits);

S3=fft(s3);

subplot(224);

plot(abs(S3));

title('滤波器处理后语音信号频谱图');

figure(4)

freqz(hn1);

subplot(211)

title('滤波器幅频特性')

subplot(212)

title('滤波器相频特性')

s3=conv(s1,hn1);

figure(5)

subplot(311);

plot(s1);

title('语音信号波形图');

subplot(312);

plot(s2);

title('加噪后语音信号波形图'); subplot(313);

plot(s3);

title('滤波后语音信号波形图');

子程序function hd=ideal_hp1(wc,N) alpha=(N-1)/2;

n=0:1:N-1;

m=n-alpha+eps;

hd=[sin(pi*m)-sin(wc*m)]./(pi*m);