[PD] derivative?

cyrille henry cyrille.henry at la-kitchen.fr
Tue Sep 4 16:40:43 CEST 2007


hello,

you can use the FIR filter of the mapping lib
sending a [1 -0.5 -0.25 -0.25< message on the right inlet to set the coeficient should be ok.

cyrille

Oded Ben-Tal a écrit :
> DPCM is Differential pulse code modulation, and its possible to get an 
> estimate of derivative with the right predictor. While the difference 
> between the last two messages is an approximation of the derivative its is 
> a really bad one so extrapulating on 4-points is much better. (dsp theory 
> is really not my area but I'm sure some people will be able to explain 
> much better about dpcm)
>   What I'm looking for is a way to:
> (1) store the last 3 values in the series. 
> (2) an estimate of the derivative should be
>   x0 - 1/2 * x1 - 1/4 * x2 -1/4 * x3 (where x0 is the most recent element)
> (3) switch places so the x0->x1 x1->x2 x2->x3 ready to do it again.
> 
> I'll try looking at list-abs (I think I tried poking around those on my 
> office mac but pd-extended couldn't find them so I left it at that).
> 
> thanks
> 
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