> even though the wavetables can be *archived* with as few as 128 or 256 > samples per wavetable (this can accurately represent the magnitude *and* > phase of each harmonic up to the 63rd or 127th harmonic), i very much > recommend at Program Change time, when the wavetables that will be used are > loaded from the archive to the memory space where you'll be > rockin'-n-rollin', that these wavetables be expanded (using bandlimited > interpolation) to 2048 or 4096 samples and then, in the oscillator code, you > do linear interpolation in real-time synthesis. that wavetable expansion at > Program Change time will take a few milliseconds (big fat hairy deal). > I know what you’re saying when you say “can be” (for many possible waves, or all waves if you’re willing to accept limitations), but to save possible grief for implementors: First, I’m sure many digital synths use 256 sample tables (and probably very common for synths that let you “draw” or manipulate wave tables), so it’s certainly not wrong. Just realize that 127 harmonics isn’t nearly enough if you expect to play a low sawtooth, filter open, with all the splendor of an analog synth. At 40 Hz, harmonics will top out at 5 kHz. As you play higher or lower notes, you’ll hear the harmonics walk up or down with the notes, as if a filter were tracking. With a full-bandwidth saw, though, the brightness is constant. That takes more like 500 harmonics at 40 Hz, 1000 at 20 Hz. So, as Robert says, 2048 or 4096 are good choices (for both noise and harmonics).
I just didn’t want someone writing a bunch of code based on 256-sample tables, only to be disappointed that it doesn’t sound as analog as expected. We like our buzzy sawtooths ;-) > On Aug 3, 2018, at 2:56 PM, robert bristow-johnson > <r...@audioimagination.com> wrote: > ---------------------------- Original Message ---------------------------- > Subject: [music-dsp] Antialiased OSC > From: "Kevin Chi" <s...@finecutbodies.com> > Date: Fri, August 3, 2018 2:23 pm > To: music-dsp@music.columbia.edu > -------------------------------------------------------------------------- > > > > Is there such a thing as today's standard for softSynth antialiased > > oscillators? > > i think there should be, but if i were to say so, i would sound like a stuck > record (and there will be people who disagree). > > > stuck record: "wavetable ... wavetable ... wavetable ..." > > > > > > I was looking up PolyBLEP oscillators, and was wondering how it would relate > > to a 1-2 waveTables per octave based oscillator or maybe to some other > > algos. > > > > thanks for any ideas and recommendations in advance, > > if you want, i can send you a C file to show one way it can be done. Nigel > Redmon also has some code online somewhere. > > if your sample rate is 48 kHz and you're willing to put in a brickwall LPF at > 19 kHz, you can get away with 2 wavetables per octave, no aliasing, and > represent each surviving harmonic (that is below 19 kHz) perfectly. if your > sample rate is 96 kHz, then there is **really** no problem getting the > harmonics down accurately (up to 30 kHz) and no aliases. > > even though the wavetables can be *archived* with as few as 128 or 256 > samples per wavetable (this can accurately represent the magnitude *and* > phase of each harmonic up to the 63rd or 127th harmonic), i very much > recommend at Program Change time, when the wavetables that will be used are > loaded from the archive to the memory space where you'll be > rockin'-n-rollin', that these wavetables be expanded (using bandlimited > interpolation) to 2048 or 4096 samples and then, in the oscillator code, you > do linear interpolation in real-time synthesis. that wavetable expansion at > Program Change time will take a few milliseconds (big fat hairy deal). > > lemme know, i'll send you that C file no strings attached. (it's really > quite simple.) and anyone listening in, i can do the same if you email me. > now this doesn't do the hard part of **defining** the wavetables (the C file > is just the oscillator with morphing). but we can discuss how to do that > here later. > > > -- > > r b-j r...@audioimagination.com > > "Imagination is more important than knowledge.” >
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