Hello,

This is for math freaks. Last week I invented a function to help detect period length in the case of missing fundamental. Well, invented? I am not a professional math person, and it may be in use since long, without me having heard about it. Anyhow I tagged it IPPASS, Instantaneous Power of Phase-Aligned Signal Segment. The function describes the squared amplitude modulation of an analytic signal segment in which phases are aligned via the amplitude spectrum. It happens to be the case that these modulations have single periodical peaks exactly in the cases where the autocorrelation function gets messed up by a dominant second harmonic. IPPASS could be useful in time domain pitch processing, I'm planning to try that shortly.

IPPASS is illustrated with plots and Pd demo patch here: http://www.katjaas.nl/ippass/ippass.html

A couple of years ago, when figuring out an attack detector, I was so much plagued by periodic amplitude modulations that they were still fresh in mind when I delved into the matter of period detection recently. That's how I got the idea to exploit the modulations this time.

Does anyone know if this function or something similar is in use for pitch tracking or another field of signal analysis? And another question: does anyone have ideas to improve stability and accuracy of a signal segment with it's phases forced to zero? It suffers from the usual boundary effects, which must be reduced to a practical minimum.

Katja