[sdiy] Good Expo curve for VCA use..

Tom Wiltshire tom at electricdruid.net
Mon Oct 15 21:00:18 CEST 2012


Hi JP,

I agree with Mattias; a typical "expo" VCA uses curve Expo2. This includes the SSM2164 or anything by THAT Corp.

However, the typical synth VCA fed by a expo ADSR is a *linear* VCA (thinking Minimoog, Pro-One, etc). The expo effect is caused by the cap charge/discharge curves on the envelope, rather than by the VCA directly. It seems to me that including an expo input on synth VCA chips got a lot more common (though by no means ubiquitous) with the later CEM stuff that was intended to be used with 1980's microprocessors and therefore with linear envelopes (CEM3378/9 for example).

HTH,
Tom


On 15 Oct 2012, at 17:02, Mattias Rickardsson wrote:

> Expo2 if you want to fade in/out slowly and evenly...
> in a dB sense, for your hearing. :-)
> 
> /mr
> 
> On 15 October 2012 17:20, Jean-Pierre Desrochers <jpdesroc at oricom.ca> wrote:
>> Hi List,
>> Suppose one have a VCA with only linear control voltage
>> inputs but want to feed it with an Expo control voltage..
>> What would be the good expo curve to use ?
>> See this picture for answer:
>> http://www.arcenson.com/public/VCA%20curves.JPG
>> 
>> Expo1 or Expo2 ?
>> A standard ADSR would generate Expo1 to this VCA
>> but I want to make sure..
>> Thanks
>> JP
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