Loads an audio file and plots its waveform and FFT

fftandplot.m

## Adapted from https://www.mathworks.com/help/matlab/ref/fft.html

function retval = fftandplot (filename, tStart, tEnd)
  
  Fs = audioinfo(filename).SampleRate;
  X = audioread(filename);
  # Convert to mono
  X = X(:,1);
  
  # Convert times to sample indexes
  iStart = round(tStart*Fs);
  iEnd = round(tEnd*Fs);
  timeDomain = [max(iStart,1):iEnd];
  L = length(timeDomain);
  # TODO does the duration have to be even?
  
  # Show original audio
  figure;
  plot(timeDomain, X(timeDomain))
  title('Original audio signal')
  xlabel('t (samples)')
  ylabel('X(t)')
  
  # Compute fft
  Y = fft(X);
  P2 = abs(Y/L);
  P1 = P2(1:L/2+1);
  P1(2:end-1) = 2*P1(2:end-1);
  
  # Show fft
  f = Fs*(0:(L/2))/L;
  figure;
  plot(f, P1)
  title('DFT of audio')
  xlabel('f (Hz)')
  ylabel('amplitude?')
  
  # Find max freq component
  [xMax, iMax] = max(P1);
  printf("Freq with highest amplitude is %d Hz\n", f(iMax))

endfunction