[PD] better tabread4~
mpuckett at imusic1.ucsd.edu
Wed Jun 11 01:52:11 CEST 2008
O can see how that could happen. I think the error in Lagrange is spread
out over all frequencies whereas I can imagine other interpolation methods
in which the error would be at frequencies closer to the original sound
(and so much harder to perceive in a situation like the one you're
On Wed, Jun 11, 2008 at 12:05:34AM +0200, cyrille henry wrote:
> 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
> 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.
> Miller Puckette a ?crit :
> >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
> >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
> >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
> >>please compile the object and look at the help patch to see the
> >>i can also send waveforme picture if needed.
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