MATLAB: Can someone explain to me what this code means?

fftfourierguitarguitar-tunertuner

Its actually a guitar tuner made by Ryann Kinnett. I tried to interact with him but unfortunately his e-mail is out. Anyway, I think I know what the program does at certain lines but mostly what I am struggling to figure out is the FFT section…

here is the links to the program http://www.mathworks.com/matlabcentral/fileexchange/26367-guitar-tuner/content/GuitarTuner.m

go to "download submisson" at the upper right if you want to run it on matlab

Cheers!!

Best Answer

2/L*abs(Y(1:NFFT/2+1)))

gives a one-sided (DC to Nyquist) amplitude spectrum. The above is the two-sided version from [-Nyquist:Nyquist] with DC in the middle.

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MATLAB: Basic question about using MATLAB fft: divide fft() by number of data points

The nextpow2 function zero-pads the signal so the fft calculation is more efficient. It adds no energy to the signal, so dividing by the length of the original signal is appropriate to normalise the amplitudes of the transformed components.

MATLAB: FFT of a damping signal

Try this:

D = load('FFT.txt');
t = D(:,1);
s = D(:,2);
Ts = mean(diff(t));                                                 % Sampling Time
Fs = 1/Ts;                                                          % Sampling Frequency
Fn = Fs/2;                                                          % Nyquist Frequency
L = length(t);
FTs = fft(s)/L;
Fv = linspace(0, 1, fix(L/2)+1)*Fn;                                 % Frequency Vector
Iv = 1:length(Fv);                                                  % Index Vector
[pks,locs] = findpeaks(abs(FTs(Iv))*2, 'MinPeakHeight',1E-3);
figure(1)
loglog(Fv, abs(FTs(Iv))*2)
hold on
plot(Fv(locs), pks, '^r')
grid
text(Fv(locs)*1.1, pks, sprintf('\\leftarrow Peak = %.5f at %.3E Hz', pks, Fv(locs)), 'HorizontalAlignment','left')

Best Answer

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MATLAB: Basic question about using MATLAB fft: divide fft() by number of data points

MATLAB: FFT of a damping signal

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