Actually hold on.. I'm being an idiot here (perhaps because saturday evening), somehow having my brain all upside down.Extreme rate change one way or another is expensive if you want to maintain the same quality (no easy way around it really, other than perhaps precomputing), because the work basically doubles for each octave. If you go 8 octaves down that's basically 2^8=256 times the work [edit: this might actually be a bit conservative, 'cos it sort of assumes single pass and we could probably use cheaper filter half way and then cleanup with a better one, etc...
Pitching down is not an issue 'cos that's equivalent to upsampling with cutoff relative to the source rate Nyquist. You just interpolate the fractional positions and cutoff remains fixed. It's going the other way that's problematic, trying to play a sample faster than recorded, 'cos then it's the target rate Nyquist that you need to honor.
I guess 8 octaves down might put some pressure on the quality of the kernel interpolation, so perhaps you need more than the usual 256 (or so) branches to avoid numerical noise becoming dominant, but like .. idk. Anything using polynomial kernels though will have issues here, you do need a proper sinc interpolator to avoid imaging.
Statistics: Posted by mystran — Sun May 19, 2024 12:25 am