PitchSpectralHps

computes the maximum of the Harmonic Product Spectrum
> called by ::ComputePitch
>
> @param X: spectrogram (dimension FFTLength X Observations)
> @param f_s: sample rate of audio data 
>
> @retval f HPS maximum (in Hz)
 ======================================================================

0001 %computes the maximum of the Harmonic Product Spectrum
0002 %> called by ::ComputePitch
0003 %>
0004 %> @param X: spectrogram (dimension FFTLength X Observations)
0005 %> @param f_s: sample rate of audio data
0006 %>
0007 %> @retval f HPS maximum (in Hz)
0008 % ======================================================================
0009 function [f] = PitchSpectralHps (X, f_s)
0010 
0011     % initialize
0012     iOrder = 4;
0013     f_min = 300;
0014     k_min = round(f_min/f_s * 2 * (size(X, 1)-1)) + 1;
0015 
0016     afHps = X;
0017     
0018     % compute the HPS
0019     for j = 2:iOrder
0020         afHps = afHps .* [X(1:j:end, :); zeros(size(X, 1)-size(X(1:j:end,:), 1), size(X, 2))];
0021     end
0022     
0023     % find max index and convert to Hz
0024     [fDummy, f] = max(afHps(k_min:end, :), [], 1);
0025     f = (f + k_min - 2) / (size(X, 1)-1) * f_s / 2;
0026     f(sum(afHps, 1) == 0) = 0;
0027 end