[sdiy] Digital Waveshape Generator.

[Roman Sowa]

Using multiple waveforms with the same sound but separate for every 
octave was commonly used in organ business. There's an old chip made by 
SGS-Thomson, which does all the work. You can upload to ROM several 
samples and it will play them accordingly to note provided by serial 
data. It does that by reading wavetable with a counter. And it 
multiplexes this job 16 times to produce 16 voices. Not to mention it 
does also attenuation (static, no aDSR inside) of the voices individually.
Works with wavetables from 16 to 2048 samples.
It's M114

Roman

W dniu 2025-07-13 o 06:55, Donald Tillman pisze:
> 
>>
>> In the case of phase-accumulator based designs with a fixed sample rate, data values may be repeated or skipped on each subsequent D/A conversion, and this process creates a mess of aliasing due to the non-bandlimited sample-rate-conversion that is occurring. Of course, many digital synths use this approach and the bright aliased harmonics are considered "sheen" to excite the LPF.
> 
> A variable sample rate oscillator, with sequential waveform values, is just playing back the samples.  The samples themselves could have aliasing issues, but those are easy to avoid, and they would just show up as harmonics of the fundamental.  (So you can always claim that you intended it that way.)
> 
> In the case of phase accumulator oscillators, any aliasing will show as non-harmonic artifacts.  That never sounds good.  So you need to address that.  It's not too difficult; use separate waveforms for higher pitches and make sure none of them alias.
> 
> Some side notes:
> 
> Oscillator waveforms in the Web Audio API are spec'd as sums of sine and cosine waves.  Similar reasoning.
> 
> My memory is telling me that the first Kurzweil keyboard used a sample for some number of consecutive notes, and a variable sample rate to avoid aliasing issues.
> 
> Tim Stilson suggests storing band-limited impulses:
>      "Alias-Free Digital Synthesis of Classic Analog Waveforms"
>      https://ccrma.stanford.edu/~stilti/papers/blit.pdf
> 
> It might also be worth considering some variation on the ARP Soloist oscillator.  Then you can play the 7/4 solo from "Cinema Show".
> 
>    -- Don
> --
> Donald Tillman, Palo Alto, California
> https://till.com
> 
> 
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