[PD] better tabread4~
mpuckett at imusic1.ucsd.edu
Tue Jun 10 18:51:34 CEST 2008
I believe "lagrange interpolation" just means polynomail. tabread4~ uses
cubic interpolation... details are in
It may be that there's a better way to do 4-point interpoation than Lagrange
but the way to find out would be by doing careful distortion measurements.
In particular, I know there are ways do do 4-point interpolation that don't
give discontinuous first derivatives, but I think most measures of distortion
would indicate using the Lagrance one instead.
On Tue, Jun 10, 2008 at 05:29:49PM +0200, cyrille henry wrote:
> Charles Henry a ?crit :
> > On Tue, Jun 10, 2008 at 4:43 AM, cyrille henry
> > <cyrille.henry at la-kitchen.fr> wrote:
> >> i realized that the 4 points interpolation in tabread4~ (and tabosc4~) are not optimal.
> > Please describe. I've analyze the interpolation formula too, and I
> > think that it is a true cubic interpolation. Is the numerical
> > accuracy bad?
> well, i think the tabread4~ interpolation is a lagrange interpolator (but i'm may be wrong).
> at least with tabread4~, the 1st derivative is not continuous, while it should be with a cubic interpolation.
> i program a cubic interpolation, and the shape of the waveform is really different.
> please compile the object and look at the help patch to see the difference.
> i can also send waveforme picture if needed.
> > Chuck
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