Plot frequency spectrum of timeseries data

plot_fft.m

function plotFFT(v,fs)
%plotFFT
%Plot the Fourier spectrum of a real-valued signal
%John J Davis IV
%john@johnjdavis.io
% Released under MIT license: https://opensource.org/licenses/MIT

% Input:
%
% v - (vector) signal
% fs - sample frequency in Hz
%
% Output:
% none, just plots the FFT spectrum and highlights dominant frequency

%No matrices allowed
if min(size(v)~=1)
    error('Input was not a vector. Did you input a matrix instead?');
end

%Column vectors only
if size(v,1) == 1
    v = v(:);
end

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 - note the change for the one middle point!
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+.05*fundHz, maxVal+0.05*maxVal, sprintf('%.2f Hz', fundHz));
hold off;
xlabel('Frequency (Hz)');
ylabel('Magnitude');
f.Children.FontSize = 16;

end