Spectral decrease for audio signals and auditory spectrograms

The spectral decrease is calculated as described in [1]:

$$\text{decrease}=\frac{{\displaystyle \sum _{k={b}_{1}+1}^{{b}_{2}}\frac{{s}_{k}-{s}_{{b}_{1}}}{k-1}}}{{\displaystyle \sum _{k={b}_{1}+1}^{{b}_{2}}{s}_{k}}}$$

where

*s*is the spectral value at bin_{k}*k*.*b*_{1}and*b*_{2}are the band edges, in bins, over which to calculate the spectral decrease.

[1] Peeters, G. "A Large Set of Audio Features for Sound Description (Similarity and Classification) in the CUIDADO Project." Technical Report; IRCAM: Paris, France, 2004.