Should I shift my fft function?

Question

Derick Trinidad 2019-12-10

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评论： Star Strider 2019-12-11

Good afternoon,

I'm trying to take the fourier transform of a recorded file. Do i need to apply the function shiftfft to the signal? If so, how do I plot the signal correctly and how do I read the graph?

%Read Voice
[y,fs] = audioread('Testing.m4a');
fourier_shift = abs(fftshift(fft(y)));
plot(fourier_shift)

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Answer 1

Star Strider 2019-12-10

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It depends on the result you want. The shifted version plots the negative and positve frequencies (the Fourier transform is symmetric). The unshifted version (plotting only half of the result) is generally more informative.

The two options:

%Read Voice
[y,fs] = audioread('Testing.m4a');
L = size(y,1);
fourier_shift = abs(fftshift(fft(y)/L));
Fn = fs/2;
freqvct = linspace(-Fn, Fn, L);
figure
plot(frqvct,  fourier_shift*2)                          % Two-Sided, With Frequency Vector
grid
fourier = abs(fft(y)/L);
Fv = linspace(0, 1, fix(L/2)+1)*Fn;
Iv = 1:numel (Fv);
figure
plot(Fv, fourier(Iv)*2)                                 % One-Sided, With Frequency Vector
grid

Choose the option you want.

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Derick Trinidad 2019-12-11

Yeah, that was a silly question. I didn't realize till much later that I didn't need to play the audio of the Fourier transform for my assignment. Thanks anyways though.