[PD] better tabread4~
cyrille.henry at la-kitchen.fr
Wed Jun 11 00:05:34 CEST 2008
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.
Miller Puckette a écrit :
> 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.
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