[PD] better tabread4~

[cyrille henry]

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
>>> <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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