Plot FFT of a signal

plotFFT.m

function plotFFT(v,fs)
%plotFFT   Quick function to plot the frequency content of a signal
% Input:
%
% v - (vector) signal
% fs - sample frequency in Hz
%

% Output: 
% none, just plots the FFT spectrum and highlights dominant frequency

%John J Davis IV

n = length(v);
detrend_v = detrend(v, 'constant');
myFFT = fft(detrend_v);
myFFT = myFFT(1:floor(n/2)); %FFT is symmetric, keep first half
freqHz = (0:(floor(n/2)-1))*fs/n;  %Frequency axis label
myFFTmag = abs(myFFT);

%Fundamental frequency, i.e. average step frequency during the run
[maxVal, fundIndex] = max(myFFTmag);
fundHz = freqHz(fundIndex);

f = figure('Position', [200 200 1000 600]);

hold on;
plot(freqHz, myFFTmag);
plot(fundHz, maxVal, 'v', 'MarkerFaceColor', 'k', 'MarkerEdgeColor', 'k',...
    'MarkerSize',8);
text(fundhz, maxVal, sprintf('%.2f Hz', fundHz));
hold off;
xlabel('Frequency (Hz)');
ylabel('Magnitude');
f.Children.FontSize = 16;


end