Problems with fft on audios

Hello, for a final project I am doing a menu with the notes do, re and mi. The problem is that when I apply the Fourier transform fft, my spectrum looks very weird. Does anyone know if I'm doing anything wrong? Code: do=audioread('do.wav'); sound(do,44100) nota=audiorecorder(44100,16,1); disp('Grabando...') recordblocking(nota,4) disp('Listo.') bb=getaudiodata(nota); audiowrite('grabacion.wav',bb,88200) audio=audioread('grabacion.wav'); audiof=fft(audio); subplot(2,1,1); plot(audio) subplot(2,1,2); plot(audiof) sound(audio,44100) Image:

[Salvador Salas Bonilla]

I'm sorry, this is the image: http://imageshack.com/a/img922/8638/lKhkl1.png

[Jan]

Please format your code using the "{} Code" button, such that it is readable. Attach images directly in the forum using the "Image" button instead of an external file hoster. Thanks.

Answer 1

[Star Strider]

In the plot you posted, you are plotting the real and imaginary parts of the two-sided Fourier transform. You need to plot the magnitude (absolute value, using the abs function) instead.

A single-sided Fourier transform is easier to understand. See the documentation on the fft (link) function for details on correctly plotting a one-sided Fourier transform.

[Salvador Salas Bonilla]

It was this, thank you very much! This was my first question here so I didn't know how to paste the code properly.

[Star Strider]

As always, my pleasure!

No worries — we were all new here once.

Answer 2

[Jan]

Did you read the documentation of fft. There you find an example for plotting:

Y = fft(audio);
L = length(audio);
FS = 44100;
P2 = abs(Y/L);
P1 = P2(1:L/2+1);
P1(2:end-1) = 2*P1(2:end-1);
f = Fs*(0:(L/2))/L;
plot(f,P1)

[Nuchto]

Thanks for this. Why did you divide by the L (length) when taking the magnitude?