Charles Henry a écrit : > On Thu, Jun 26, 2008 at 12:36 PM, cyrille henry > <[EMAIL PROTECTED]> wrote: > >> then, it's possibile to have interpolation using more points, and also >> interpolation that offer antialiasing. >> >> BTW : i just commited a tabosc4aa~ (aa is for anti aliasing). >> this is also just a test. >> it's far from perfect, but lot's better than the original tabread4~ when >> dealing with high pitch transposition. >> for now, i did this with a classic 8x upsampling + biquad filter inside the >> tabread4aa~ (ok, this is more cpu intensive : about 1 to 1.5 % cpu) >> before i'm doing more work on this, did anyone have experience with this? > > To me, the upsampling is not a good approach for anti-aliasing. This > means, you have to interpolate, then filter, then sample again. yes, i know. but it's this way i've got the best result. if anyone want to try something else....
> > But you will wind up applying your filter at a lot of points, which > will just be discarded. the current implementation use a 4 time upsampling, so it's not so inefficient, the result are quite good. > > In fewer steps, (I think) we can modify the interpolation function > continuously as the speed changes. Rather than filtering on a long > signal, just filter it in place. The part that gets tricky is that > the DFT is a lot less relevant, and you have to rely upon continuous > functions instead. Shannon interpolation use sinc function. with 16 points interpolation i was not able to have the same quality as the 4 times oversampled 4 points interpolation plus you also have to compute a 2D table of sinc function for improving performance (so you also have to interpolate in this 2D table). maybe it's the way to do a 128 points, very heavy, but almost perfect sounding interpolation that could be used in non real time. i should give it an other try, but i think i'll not have the time soon. (will finish the other one thirst). anyway, i don't know a lot's on this subject, so any help is welcome cyrille > > I didn't make any progress today... and friday is gone for sure :) I > will calculate the spectrum for tabread4c~ on Saturday, I think. > > I'm down with the project, but I can't really see the big picture for > a tabread/vd/tabosc lib yet. > > Chuck > > _______________________________________________ > Pd-list@iem.at mailing list > UNSUBSCRIBE and account-management -> > http://lists.puredata.info/listinfo/pd-list > > _______________________________________________ Pd-list@iem.at mailing list UNSUBSCRIBE and account-management -> http://lists.puredata.info/listinfo/pd-list