On Thu, Jun 26, 2008 at 12:36 PM, cyrille henry cyrille.henry@la-kitchen.fr 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.
But you will wind up applying your filter at a lot of points, which will just be discarded.
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.
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