Harmonic Spectral Smoothness
A peak based calculation of smoothness. Caculated by evaluting the log of a
partial minus the average of the log of the surrounding partials. Is based
upon Stephan McAdams Spectral Smoothness in (McAdams 1999).
McAdams, S. 1999. Perspectives on the contribution of timbre to musical
structure. Computer Music Journal. 23(3):85102.
