# [CM] Finding the duration of a time-varying resampled sound.

**Kjetil S. Matheussen
**
k.s.matheussen@notam02.no

*Tue, 28 Oct 2003 13:36:18 +0100 (MET)*

On Tue, 28 Oct 2003, Kjetil S. Matheussen wrote:
>*
*>*
*>* On Tue, 28 Oct 2003, Bill Schottstaedt wrote:
*>*
*>* > > What I need is a general formula for the scale-factor 's'
*>* > > between two points (x1,y1) and (x2,y2), where y1 and y2 are
*>* > > always positive values.
*>* >
*>* > I think you want the average of the inverse; the "tempo map"
*>* > idea here would be to integrate the inverse of the envelope,
*>* > then multiply that by the in-coming note length. But for
*>* > each segment, I think this would do it:
*>* >
*>* > (define (invert-average x1 y1 x2 y2)
*>* > (/ (- x2 x1) (* .5 (+ y1 y2))))
*>* >
*>* > (Didn't actually test this...)
*>*
*>* This is more or less exactly what I do now, and which does not
*>* work.
*>*
*Sorry, I didnt read your mail well enough. This
function just finds the inverted average. But
how does the integration function look like?
I have a feeling its something like
(something (* 0.5 (* invertaverage invertaverage))
something2)
but I dont know enough math to figure out how
to make the function. And I have tried. :)
(all sunday actually)
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