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1、实验三1读取，WAV格式文件2.得到频谱3.设计滤波器，对信号滤波4.比较滤波前后的差异(频谱或回放)%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%参数初始化%%%%%%%%%%%%%%%%clearall;%关闭以往仿真的数据桟[Y,fs,bits]=wavread(1I:等——分钟•wav1,[10000001800000]);%读出信号1，采样率和采样位数n=length(Y);%求采样信号1的长度t=0:l/fs:(n-l)/fs;%求采样信号1吋域上的采样点数sound(Y,fs);%读出加噪声后的采样信号%%%
2、%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%构造巴特沃思滤波器%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%figure(1);%画出zhang加噪声后的时域图subplot(1,2,1)plot(t,Y);xlabel(*时间(t)’)；ylabel(’幅度(Y)•);title(’吋域图1);gridon;subplot(1,2,2)plot(abs(fft(Y)));xlabel('频率(f)
3、’);ylabel(’幅度(Y)，);title('频谱图*>;gridon;%%%%%%%%%%%%%%构造800Hz的带阻滤波器%%%%%%%%%%%%%f0=800;%fc=20;%设定过渡带的频率Rp=l;%通带区的波纹系数Rs=30;%阯带区的波纹系数%wp=[(f0-fc)/(fs/2)(f0+fc)/(fs/2)];%通带的拐角频率%ws=[(f0-5*fc)/(fs/2)(f0+5*fc)/(fs/2)];%阻带的拐角频率wp=200*2*pi/(fs/2);ws=300*2*pi/(fs/2);[N,wc]=fc>tittor
4、d(wp,ws,Rp,Rs,’s’)；％求出巴特沃思滤波器的阶数1^及频率参数wc[num,den]=butter(N,wc,1low’)；%求出巴特沃斯低通数卞•滤波器的传递函数模型系数[h,w]=freqz(num,den,fs);%求出离散系统频率响应的数依figure(2);subplot(1,2,1);%M出低通滤波器的幅频特性图plot(w*fs/(2*pi)z20*logl0(abs(h)));xlabel(*频率(w)’);ylabel(’幅度(h)’)；title(’幅频特性网1);gridon;B=filter(num,de
5、n,Y);%对含噪信号Y进行低通滤波subplot(1,2,2);%M出低通滤波器滤去;C•的吋域图plot(t,B);xlabel(’时间(t))•);ylak)el(*幅度(B)•);title(’用低通滤波器滤后的时域图*);gridon;figure(3)plot(abs(fft(B)));xlabel(：频谱(f))’)；ylabelU幅度(B)1);title(’用低通滤波器滤后的频谱图1);gridon;%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%均值滤:波％%%%%%%%%%%%%%%%%%
6、%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%读出和写出滤波后的语音信号%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%pause(10);%暂停20swavplay(Bzfs);%读出滤去800Hz和200Hz和50Hz噪声后的采样信号%wavwrite(B,fs,16,1designedby刘其飞巴特沃思滤波器滤波后的语音信号.wav、)；％写出滤波后的语音信号Figure1■n频谱图FileEditViewInsertToolsDes
7、ktopWindowHelpBad%xa®k士s□b时域图ym42•o.0.80.64.2onu-o-04-0.6-0.80510152.510.505频率(f)25穆(A)侧题200时间⑴10x105reFileEditViewInsertToolsDesktopWindowHelpQ己B螓Ikl虱'O®猖□012频率（w）3te频特性圈-innx10405101520时间＜t))1505oCJ>用低通滤波器滤后的时域图Figure3’BiEditViewInsertToolsDesktopWindowHelpd己sy^ifei吟'o®遲z，
8、isi口x1052.51(a)鹧Is用低通滤波器滤后的频谱图
