Thank you very much :) By the way, I have just tried Spectral Flatness (as defined in Wikipedia) and it seems promising.
I attach an abstraction that outputs spectral flatness in PD-vanilla. 2008/1/18, Jamie Bullock <[EMAIL PROTECTED]>: > > Hi, > > On Fri, 2008-01-18 at 14:04 +0100, matteo sisti sette wrote: > > 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... > > The irregularity metric is generally computed on the magnitude spectrum, > but there is no reason not use it on the harmonic spectrum, as some > authors do. It is just giving you a measure of the 'jaggedness' of a > given sequence of numbers, you could use it on any distribution, e.g. > you could take the irregularity measure of the numbers of Pd mailing > list postings over a 12 month period! > > For the purposes of computing noise content it makes sense to use the > mag spectrum. Some authors e.g. Park (2004) use the log magnitude > spectrum. > > > 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..... > > It depends which formula you use. Using Krimphoff ('Irregularity I' in > libxtract), a high irregularity value corresponds to high noise content. > The relationship is approximately inverted if you use Jensen. > > I performed an analysis in Sonic Visualiser using a sound that contains > a linear crossfade between a 440Hz sine wave and white noise. The > results can be found at: > > http://www.postlude.co.uk/incoming/sine-noise/sine-noise.png > > The red line shows Irregularity calculated via Krimphoff's method, the > blue line shows Jensen. > > The audio file I used is at: > > http://www.postlude.co.uk/incoming/sine-noise/sine-noise.wav > > > Jamie > > -- > www.postlude.co.uk > > -- Matteo Sisti Sette [EMAIL PROTECTED] http://www.matteosistisette.com
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