[PD] better tabread4~

[Miller Puckette]

I believe "lagrange interpolation" just means polynomail.  tabread4~ uses
cubic interpolation... details are in
   http://crca.ucsd.edu/~msp/techniques/latest/book-html/node31.html

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.

cheers
Miller

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.
> 
> 
> cyrille
> 
> 
> > 
> > Chuck
> > 
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> 
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