audio spectrum - need help with the Matlab code

[littleheadyu]

audio spectrum spikes

Hi,

I am trying to analyze the spectrum of an audio .wav file which was recorded by someone else.
The .wav file has two tracks in it, so I just used one of them. The sampling rate is indicated in the file properties as 44 kHz.
I wrote the Matlab code as below:

sound=wavread('081029_08.wav');
a=sound,1);
b=abs(fftshift(fft(a)));
N=length(b);
Fs=44000;
f=(Fs/N)*(-N/2+1:N/2);
plot(f,b);

The spectrum seems strange, the spike is at f=0...
Can anyone explain the reason for me? I attached the .wav file with this post.

Thanks in advance!

Yuping

 

[Audioguru]

audio spectrum + wavread

I don't have Matlab. So I used the spectrum analyser in my pc and my ears instead.

It is wind hitting the diaphragm of a microphone and producing DC (the spike at f=0) and extremely low frequencies.

Since most of the peaks are at the same level then I think the mic or the preamp is clipping.

 

[pauloynski]

Re: audio spectrum

I agree with Audioguru. Seems to be wind hitting a microphone. The final part of the record is definitely clipped and also shows a poor low frequency response of the pre-amp.

 

[FvM]

Re: audio spectrum

The spectrum seems strange, the spike is at f=0

If the input signal isn't exactly DC-free, it's rather normal, not strange. Simply remove the DC component and examine the remaining spectrum.