# [PD] [OT] spectral irregularity to measure noisiness (was Re: about fiddle~)

matteo sisti sette matteosistisette at gmail.com
Fri Jan 18 14:04:59 CET 2008

Hi,

Jamie Bullock wrote:

> I find spectral irregularity to be quite a good noisiness metric,
> [...]
> Krimphoff:
> Irregularity = \sum_{k=2}^{N-1} |a_k - \frac{a_{k-1} + a_k + a_{k+1}}{3}|
> Jensen:
> Irregularity = \frac{\sum_{k=1}^{N} (a_k - a_{k+1})} {\sum_{k=1}^Na_k^2}
> [...]
> Where a_k is the amplitude of the kth coefficient in the magnitude spectrum.

I googled a little bit, and as far as I understand, these definitions
seem to apply to an harmonic sound, and a_k seems to be the amplitude
of the k-th partial... that is the sound is supposed to be pitch and
its spectral peaks (partials) have already been extracted...

Would it make any sense to apply the above formulas using just the
magnitude spectrum coefficients of the whole spectrum as a_k??
If so, I'm not sure whether a high irregularity should be expected to
correspond to a high or low noisiness.....