[sdiy] samp. freq for ADSR ?

[Andre Majorel]

On 2004-04-02 16:35 +0100, Richard Wentk wrote:
> At 17:09 02/04/2004 +0200, jbv wrote:
>
> >OK, 48 KHz is a theorically fine sampling freq for audio signals.
> >But right now I'm brainstorming on a project in which multiple
> >ADSR signals would be generated by a uC / DAC / S&H.
> >What is the optimal freq at which each signal should be refreshed /
> >incremented ?
> >At first glance 48 KHz seems a luxury, but what about very fast
> >AD ?
> 
> The shortest useful time for an envelope attack is 1ms. You can go for 
> 100us if you want to get really obsessive, but 1ms will do for most things.
> 
> Sampling at 4KHz would give you 4 samples for the attack phase. That 
> doesn't like a lot, but it's likely to be enough.
> 
> 4KHz would also give you LFOs up to 2KHz, which should be enough for most 
> things.

At 4 kHz, you'll have to LP filter the output of the DAC, or the
steps will create noise in the audio band, no matter how many bits
of resolution you have.

The advantage of sampling at 20 kHz or more is that you can
dispense with the filtering (or so I think).

-- 
André Majorel <amajorel at teaser.fr>
http://www.teaser.fr/~amajorel/