数字信号处理实验报告实验三哈工程.doc

实验三抽样3.1正弦信号混叠 A.程序： nn=0:79; sinus=sin(2*pi*300/8000*nn); stem(nn,sinus).b.程序： plot(nn,sinus) .c. nn=0:79;sinus=sin(2*pi*100/8000*nn); x1=sinus; nn=0:79;sinus=sin(2*pi*225/8000*nn); x2=sinus; nn=0:79;sinus=sin(2*pi*350/8000*nn); x3=sinus; nn=0:79;sinus=sin(2*pi*475/8000*nn); x4=sinus; subplot(411),stem(nn,x1); subplot(412),stem(nn,x2); subplot(413),stem(nn,x3); subplot(414),stem(nn,x4);3.3产生信号a,n=0:1000;f0=1000;fsim=80000;t=n./fsim;x=cos(2*pi*f0*n/fsim);subplot(211),stem(n,x);title(SAMPLES),ylabel(x(t),xlabel(n);subplot(212),plot(t,x);title(CONTINIOUS),ylabel(x(t),xlabel(t)c.fmagplot函数m文件：function fmagplot(xa,dt)L=length(xa);Nfft=round(2.round(log2(5*L);Xa=fft(xa,Nfft);range=0:(Nfft/4);ff=range/Nfft/dt;plot(ff/1000,abs(Xa(1:length(range)title(CONT-TIME FOURIER TRANSFORM(MAG)xlabel(FREQUENCY(kHz),grid;Pausefmagplot(x,1/fsim)3.4 A/D转换a.fsim=80000;fs=8000;k=fsim/fs;n=0:1000;l=length(n);x=cos(2*pi*1000*n/fsim);y=x(1:k:l);L=length(y);n1=0:L-1;stem(n1,y)title(AD),ylabel(xn),xlabel(n)b.H,W=dtft(y,1000);plot(W,abs(H);title(DTFT AD),ylabel(X(jw),xlabel(w)3.5设计一个重建滤波器B.fsim=80000; f0=1000;fs=8000;y2=zeros(1,L);for i=0:L1-1; y2(i*delta+1)=y(i+1);endfcut=2*(fs/2)/fsim; b,a=cheby2(9,60,fcut); x1=delta*filter(b,a,y2); c,d=freqz(b,a,1000,whole);d(501:1000)=d(501:1000)-2*pi;d=fftshift(d);d=d/2/pi/1000*fsim;c=fftshift(c);plot(d,abs(c);ylabel(|H(jomega)|);xlabel(FREQUENCY(kHz);3.6 D/A转换：a.y2=zeros(1,L);for i=0:100; y2(i*10+1)=y(i+1);endyy=filter(b,a,y2);t=0:0.001:1;plot(t,yy)ylabel(xr(t),xlabel(t)b.fmagplot(yy,0.0000125)3.7测试混叠function x,x1,y,y1,y2=testall(f0,fs,fsim)n=0:1000; fsim=80000; dt=1/fsim; t=n./fsim; x=cos(2*pi*f0*n/fsim); delta=round(fsim/fs); L=length(x); y1=zeros(1,L);y1(1:delta:L)=x(1:delta:L);y=x(1:delta:L);L1=length(y);n1=0:L1-1;Nfft=round(2.round(log2(5*L); Xa=fft(x,Nfft);range=0:(Nfft/4);ff=range/Nfft/dt;H,W=dtft(y,L); w1=W/2/pi/1000*fs;y2=zeros(1,L);for i=0:L1-1; y2(i*delta+1)=y(i+1);endfcut=2*(fs/2)/fsim; b,a=cheby2(9,60,fcut); x1=delta*filter(b,a,y2); M=length(x1);Nfft1=round(2.round(log2(5*M); X=fft(x1,Nfft1);range1=0:(Nfft1/4);ff1=range1/Nfft1/dt;subplot(223);plot(t,x1);grid;title(Xr(t);xlabel(t);subplot(224);plot(ff1/1000,abs(X(1:length(range1);title(|Xr(jomega)|);xlabel(kHz);subplot(221);plot(t,x);grid;title(X(t);xlabel(t);subplot