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 > > <[EMAIL PROTECTED]> 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 > > > > _______________________________________________ > > [email protected] mailing list > > UNSUBSCRIBE and account-management -> > > http://lists.puredata.info/listinfo/pd-list > > > > > > _______________________________________________ > [email protected] mailing list > UNSUBSCRIBE and account-management -> > http://lists.puredata.info/listinfo/pd-list _______________________________________________ [email protected] mailing list UNSUBSCRIBE and account-management -> http://lists.puredata.info/listinfo/pd-list
