[PD] tabread4~ "broken" interpolation algorithm - was Re:, Max Smoother Audio than Pd?

Matt Barber brbrofsvl at gmail.com
Tue Mar 30 16:40:11 CEST 2010


On Tue, Mar 30, 2010 at 9:52 AM, Matteo Sisti Sette
<matteosistisette at gmail.com> wrote:
> Matt Barber escribió:
>>
>> Yes, as far as I know it's identical -- when you do one of these
>> interpolations with four points, you can either think of it in terms
>> of a cubic polynomial formula involving those four points, or in terms
>> of the sum of four scaled "basis functions" - the latter seems to me
>> intuitively equivalent to direct convolution of an impulse response
>> centered on the four points, and scaled to each.  It will be limited
>> by the quantization of the index, so in that sense it might not be
>> linear..
>
> Hmm, by linear I mean that the interpolated version of the sum of any two
> discrete signals is equal to the sum of the interpotated versions of each
> one. It shouldn't be difficult to tell whether this is true or not by
> looking at the formulas but I'm too lazy right now :P


Right, I think it should absolutely be linear in that sense, provided
you used exactly the same index for both processes and ignored any
rounding errors from adding samples.  "In math" it should be linear,
but I'm not 100% sure about what quantization of index or sample does
to it (we often don't worry so much about it anyway).




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