ok, thanks for the answer. i understand what's in your book, but i found other references where cubic interpolation is used for a function that offer continuity of the 1st derivative.
i can understand that tabread4~ minimise the error when the table is large (when you play it faster than the original speed). but with a small table, or when you play it slower, the first derivative discontinuity create lot's of high frequency. So, in this condition, the function i use offer a better quality. see in the svn externals/nusmuk/tab/tabosc4c~-help.pd for more. cyrille Miller Puckette a écrit : > 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 >>> >>> _______________________________________________ >>> Pd-list@iem.at mailing list >>> UNSUBSCRIBE and account-management -> >>> http://lists.puredata.info/listinfo/pd-list >>> >>> >> _______________________________________________ >> Pd-list@iem.at mailing list >> UNSUBSCRIBE and account-management -> >> http://lists.puredata.info/listinfo/pd-list > > _______________________________________________ > Pd-list@iem.at mailing list > UNSUBSCRIBE and account-management -> > http://lists.puredata.info/listinfo/pd-list > > _______________________________________________ Pd-list@iem.at mailing list UNSUBSCRIBE and account-management -> http://lists.puredata.info/listinfo/pd-list