[sdiy] MIDI DCOs

[Antti Huovilainen]

On Thu, 15 Jan 2004, Brandon Daniel wrote:

> >why?
> >whats wrong with DSP generated waveforms?
> I guess that depends on the waveforms, the way they're generated, their
> DACs and the DACs clock rate.

Unlike many people think, generating good waveforms in DSP is not easy.
If one simply generates a trivial sawtooth (adder that wraps), it will
alias horribly and sound very nasty, especially on high notes.
For traditional analog waveforms, minBLEP is probably the best method.
(see http://www.cs.cmu.edu/~eli/papers/icmc01-hardsync.pdf)
The downside is that for frequencies higher than about Fs/12, the cpu
usage doubles per octave.
For wavetable oscillators, one should use mipmapping and very good
interpolation (or pre-oversampling the wavetables).

Overall 2x oversampling helps a lot with both oscillators (good
interpolation that doesn't attenuate much below Fs/2 is very costly)
and filters (which get a lot worse at frequencies near Fs/2).

Antti

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