Quick Question About Signal Processing

[Ahmed Husain ?Abbas Mohamed Sahrab]

Dear Esteemed Volunteers.

I have a question about incorporating a piece of code into my project.

I have found this piece of code online

   Fs = 1000;
    t = 0:1/Fs:1-1/Fs;
    x = cos(2*pi*100*t)+randn(size(t));
    [Pxx,F] = periodogram(x,[],length(x),Fs);
    plot(F,10*log10(Pxx))

and I would like to use the wavread command and use that signal in place of the Fs,t and x. So, I wrote this bit of code

[y, fs]= wavread('song1.wav');

NFFT=input("Choose a fraze size of either 128, 256 and 512. ");

[Pxx,F] = periodogram(y,[],NFFT,fs);

plot(F,10*log10(Pxx))

But I am sad to report this it is not working, and that I am receiving this error

⹏፥error: periodogram: X must be a real or complex vector

If you can help me I would appreciate it immensely 

With Love,

Ahmed Suhrab