[sdiy] Log/Expo or Lin VCAs for digital control?

[Tom Wiltshire]

> On 3 Nov 2017, at 18:15, Dave Magnuson <abide at dmdrafting.com> wrote:
> 
> -----Original Message-----
> From: Synth-diy [mailto:synth-diy-bounces at synth-diy.org] On Behalf Of Tom Wiltshire
> Sent: Friday, November 3, 2017 1:34 PM
> To: paula at synth.net
> Cc: SYNTH DIY
> Subject: Re: [sdiy] Log/Expo or Lin VCAs for digital control?
> 
> 
> True, for modulation depth control, liners probably always going to be best. I was thinking more of audio. For some reason (availability?) the final VCA in most classic synths is linear. Doesn’t make sense to me.
> 
> Tom
> 
> 
> Is it because the envelopes are usually expo shaped? (not sure myself actually)

If you look at the situation at the time, I think it’s a combination of OTAs being linear and the typical analog RC envelope giving the expo shape you’d probably want. In combination, that’s too easy to resist. You could add an exponential convertor stage to the OTA (there are examples in synth history - Roland 100M faked it with a transistor, IIRC) but then you’d have to do something about the envelope, so why bother? That’s my guess, for what it’s worth.

Nowadays though, the situation is different. Expo VCAs are easily available and are better quality than linear OTAs. Analog envelopes aren’t the only option, so changing the envelope behaviour is not so hard as it was.

Tom