On 7/3/18 7:23 AM, alexandre niger wrote:
Thank you for all the help. Gain loss was finally fixed after normalizing. In an other hand, using fft and inverse effectively gave better results than FIR or IIR. With very rich signals, I can still hear an harmonic difference between WTs. I guess I could fix it by using more WTs than one every octave. I will try every 6 semitones.
other times this topic has come up, i have said exactly that. if your sample rate is 48 kHz and you're willing to settle for a top bandwidth of 19.8 kHz, (so with a fixed LPF you are gonna kill anything that survives between 19.9 and 24 kHz, two wavetables per octave will do it. so at the bottle of the 6 semitone split, your wavetable will have harmonics up to 19 kHz, as you increase the pitch to 6 semitones higher (that's a frequency ratio of sqrt(2)), that 19.8 kHz becomes 28.1 kHz, which folds over (reflects about 24 kHz) to 19.9 kHz. that's your worst case. so just blow away everything above 19.8 kHz with a single fixed and sharp LPF. but since memory is cheap, there should be no reason you can't go to 3 wavetables per octave. or not even an integer. say one wavetable for every 5 semitones. no reason you can't do that either.
with 96 kHz sample rate, it's much less of a problem regarding aliasing above 24 kHz and you can relax your specs with that LPF and the number of wavetables per octave.
i would suggest mixing or crossfading from the wavetable that is richer in harmonics to the wavetable missing a few as your note slides up and down the keyboard. like if you have a wavetable at every C and every F#, when the note is F, it should be 1/6 scaling the wavetable at C and 5/6 scaling the wavetable at F#. when the note is an A, it should be 1/2 of the wavetable at the F# below and 1/2 of the wavetable at C above.
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