How to get specific signal from an audio file

I am trying to extract Electrical Network Frequency signal and plot it like frequency vs time from an uncompressed audio file (.wav)

I tried to do something like this:

[y,fs]=wavread('exercise.wav');
t=0:1/fs:(length(y)-1)/fs;
figure(1);
plot(t,y);
L = 512;
window=hamming(L); 
noverlap=floor(L/2);; 
nfft=1024; 
figure(2);
view(0,90);
spectrogram(y,window,noverlap,nfft,fs);

But all I got are two graphics without ENF signal in them.

Anybody knows how to get Electric Netowrk Signal form audio file?

Answer 1

[Walter Roberson]

http://www.mathworks.com/matlabcentral/answers/142645-how-to-extract-enf-electrical-network-frequency-form-audio-signal-i-want-extracted-enf-pattern-fr

[Lolipop]

This answer you gave me predict that I am using 50Hz network, but this signal could be recorded with 60Hz power network..

[Walter Roberson]

If you cannot read that source and make the three trivial changes to the code, then you clearly do not understand the code and need to study it before you hand in your homework assignment.