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

[Miller Puckette]

Hi all-

I haven't looked at Cyrille's interpolator but... tabread4~ uses true cubic
interpolation (which perhaps Cyrille's object also does in some other way).
The tabread4~ algorithm is to put a cubic through the 4 points surrounding
the input point.  However, this cubic curve does not necessarily match the
next curve over in first derivative.

A workaround is to up-sample everybody by a factor of 2 - this dramatically
reduces error, usually by 24 dB.

All described in chapter 2 of my book,
http://crca.ucsd.edu/~msp/techniques.htm

cheers
Miller

On Mon, Mar 29, 2010 at 02:29:30PM +0200, Matteo Sisti Sette wrote:
> Roman Haefeli escribi??:
> 
> >Check this thread:
> >http://lists.puredata.info/pipermail/pd-list/2008-06/062878.html
> 
> I checked it out (not read the _whole_ thread to the end) but,
> In what way can the current tabread4~ interpolation, which is 
> discontinuous even in its 1st derivative, be superior to true cubic 
> interpolation? Even at transpositions near to zero, I can't see what's 
> the advantage, nor what it is supposed to minimize.
> 
> -- 
> Matteo Sisti Sette
> matteosistisette at gmail.com
> http://www.matteosistisette.com
> 
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