MATLAB: Help with Fourier analysis of wav signal

fft

Hey I am trying to understand this fft waveform i have with a .wav file I recorded of myself. I feel as though the fft is not right, or I am misunderstanding what is being shown. I posted the fft and it shows the signal having a frequency components magnitude increasing at frequencies much higher than my voice. I think the frequency range should be in the range of 250-350Hz. Can anyone explain what I am not understanding? I also added the time domain representation of the wave.

Here is my code.

Mono = (y(:,1)+y(:,2))/2;
y = Mono;
time=(1:length(y))/Fs;
F = 1./time;
nfft = fft(y);
plot(F,nfft)

Best Answer

For the correct way to code and interpret the Fourier transform of your signal, see the R2015a documentation for the fft (link) function. Particularly note the code between the first (top) two plot figures.

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MATLAB: Understanding FFT analysis of sound .wav file

That looks appropriate for a speech signal. Speech is generally considered to be band-limited to a maximum frequency of 6 kHz, and in the analog telephone days was actually limited to 6 kHz, and radiotelephone transmitters limited it to 3 kHz to conserve bandwidth. The fundamental is usually in the range of 500-1200 Hz (lower for males and higher for females). There are probably more references available, but the most appropriate one i can find just now is Human Speech Spectrum, Frequency Range, Formants.

MATLAB: Fft of a 2 simple cos functions

Replace the following line:

   f=(0:nfft/2-1)*Fs/nfft/2;

with:

   f=(0:nfft/2-1)*Fs/nfft;

Best Answer

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MATLAB: Understanding FFT analysis of sound .wav file

MATLAB: Fft of a 2 simple cos functions

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