FeatureSpectralDecrease

computes the spectral decrease from the magnitude spectrum
> called by ::ComputeFeature
>
> @param X: spectrogram (dimension FFTLength X Observations)
> @param f_s: sample rate of audio data (unused)
>
> @retval vsk spectral decrease
 ======================================================================

0001 %computes the spectral decrease from the magnitude spectrum
0002 %> called by ::ComputeFeature
0003 %>
0004 %> @param X: spectrogram (dimension FFTLength X Observations)
0005 %> @param f_s: sample rate of audio data (unused)
0006 %>
0007 %> @retval vsk spectral decrease
0008 % ======================================================================
0009 function [vsd] = FeatureSpectralDecrease (X, f_s)
0010 
0011     % compute index vector
0012     k = 0:size(X, 1)-1;
0013     k(1) = 1;
0014     kinv = 1 ./ k;
0015     
0016     % compute slope
0017     vsd = (kinv*(X-repmat(X(1, :), size(X, 1), 1))) ./ sum(X(2:end, :), 1);
0018        
0019     % avoid NaN for silence frames
0020     vsd (sum(X(2:end, :),1) == 0) = 0;
0021 
0022 end