求助一段matlab程序的意思
 

小弟是大四应届毕业生，学校发狠提前答辩，自己的两段matlab程序还没有看懂，希望论坛的大大们能够帮帮忙，解释一下每一句的意思，能够让我在答辩的时候说清楚就成！
第一段：
[y,Fs,bits]=wavread('file name');
y=y(:,2); sigLength=length(y);
Y = fft(y,sigLength);
Pyy = Y.* conj(Y) / sigLength;
halflength=floor(sigLength/2);
f=Fs*(0:halflength)/sigLength;
figure;plot(f,Pyy(1:halflength+1));xlabel('Frequency(Hz)');
t=(0:sigLength-1)/Fs;
figure;plot(t,y);xlabel('Time(s)');
第二段：
[k,Fs,bits]=wavread('file name');
k=k(:,1);
y_temp=k(1:90000);
dfactor=3;
y=decimate(y_temp,dfactor);
[b,a] = butter(10,200/(Fs/(dfactor*2)),'high');
y=filter(b,a,y);
y=interp(y,dfactor);
sigLength=length(y);
Y = fft(y,sigLength);
Pyy = Y.* conj(Y) / sigLength;
halflength=floor(sigLength/2);
f=Fs*(0:halflength)/sigLength;
figure;plot(f,Pyy(1:halflength+1));xlabel('Frequency(Hz)');
sigLength=length(y_temp);
Y = fft(y_temp,sigLength);
Pyy = Y.* conj(Y) / sigLength;
halflength=floor(sigLength/2);
f=Fs*(0:halflength)/sigLength;
figure;plot(f,Pyy(1:halflength+1));xlabel('Frequency(Hz)');
t=(0:sigLength-1)/Fs;
figure;plot(t,y,t,y_temp);xlabel('Time(s)');
wavplay(y,Fs);