On Sat, Feb 28, 2009 at 8:25 PM, David Doukhan david.doukhan@gmail.com wrote:

I don't even know what method have been used in vd~ ... The only thing I've read in the corresponding help patch, is that the interpolation method used by that component does an interpolation over 4 values. Does anyone know the name of the method used by that component? It would allow me get better clues on its theoretical efficiency, and to know if spending some time to program/test some alternative method would be usefull...

vd~ appears to use the same 4-point interpolation method as tabread4~, which is just a cubic polynomial fit through 4 points. Other methods of finding interpolation polynomials for improved response were discussed a few months ago in the thread on different tabread4's. Let me know if you need anything.

Chuck

http://lists.puredata.info/pipermail/pd-list/2008-06/062878.html http://lists.puredata.info/pipermail/pd-list/2008-06/063256.html http://lists.puredata.info/pipermail/pd-list/2008-06/063303.html

I did a lot of analysis on the functions, involved. big math lecture is here: http://lists.puredata.info/pipermail/pd-list/2008-07/063601.html tables and transforms: http://lists.puredata.info/pipermail/pd-list/2008-07/063489.html

Algorithm is here in d_delay.c:

262 while (n--) 263 { 264 t_sample delsamps = x->x_sr * *in++ - zerodel, frac; 265 int idelsamps; 266 t_sample a, b, c, d, cminusb; 267 if (delsamps < 1.00001f) delsamps = 1.00001f; 268 if (delsamps > limit) delsamps = limit; 269 delsamps += fn; 270 fn = fn - 1.0f; 271 idelsamps = delsamps; 272 frac = delsamps - (t_sample)idelsamps; 273 bp = wp - idelsamps; 274 if (bp < vp + 4) bp += nsamps; 275 d = bp[-3]; 276 c = bp[-2]; 277 b = bp[-1]; 278 a = bp[0]; 279 cminusb = c-b; 280 *out++ = b + frac * ( 281 cminusb - 0.1666667f * (1.-frac) * ( 282 (d - a - 3.0f * cminusb) * frac + (d + 2.0f*a - 3.0f*b) 283 ) 284 ); 285 }