[sdiy] Oberheim Xpander Envelopes and LFOs etc

[Colin f]

> So the question is "How low can you go?". 53Hz might be 
> really silly,  
> but would 1KHz be enough? 5KHz? I know some of the software sound  
> languages (csound or puredata) use rates of 6KHz or so.
> 
> What counts as a reasonable sampling rate for LFOs and Envelopes?

That really sounds to me like a question you should answer with your own
ears, but...
According to Nyquist, sampling rate should be at least double the
(band-limited) maximum frequency you want to reproduce.
If you consider the rise and fall of the attack/decay phase of an envelope
generator to be a single cycle of a wave, then your sample period must be
less than or equal to the minimum attack or decay time. Make those 2ms, and
500Hz should be OK.
Of course, that gives you a slightly different shape to a real analogue
envelope generator - the sharp corner as you go from 0 to the maximum
initial gradient of the attack phase is rounded off by the band-limiting
filter.
If that makes any audible difference, increase the sample rate until you're
happy.

Cheers,
Colin f