[sdiy] Lin/Log VCAs and envelopes - compensating for log VCAs

[Simon Brouwer]

Hi Tom,
 
To my ears, linear slope envelope generators (as found in many digital
synthesizers, as a linear slope is so much easier to calculate) are vastly
inferior to exponential slope ones, as at the end of the decay phase the
envelope does not gradually evolve into the sustain level, but switches from
changing into static all at once. This often results in a sound that is
interesting in the beginning, but loses all life in the sustain phase, or is cut
off in an unnatural way. Layering and/or lots of reverb may mask this to an
extent but that is just stopgap. Real synthesizers have curves!
 
A linear decay combined with an exponential control/gain VCA will give an
exponential decay of amplitude, but only if the sustain level is 0. With nonzero
sustain levels the envelope will again switch from changing to static all at
once.
 
 
Best regards
Simon
 
> Op 11 februari 2016 om 15:47 schreef Tom Wiltshire <tom at electricdruid.net>:
>
>
> Yeah, I've done the same thing. My PIC VCADSR has linear or exponential
> envelopes selectable. But that's not exactly what I'm suggesting here.
>
> Instead, I was thinking of doing a normal exponential ADSR for use with a
> linear VCA, and a "log compensated" ADSR for use with a log VCA. This would
> have a linear decay and release, but an extreme curve to the attack section to
> give the typical shape even with the log VCA.
>
> Tom
>
> On 11 Feb 2016, at 09:14, Roman Sowa <modular at go2.pl> wrote:
>
> > It was too easy not to implement it, so I did that on my EG too. One switch
> > determines exponential or almost-linear curve for attack and the other one
> > for 1st decay. It simply changes the voltage charging the timing capacitor.
> > Here's example scopeshot of both settings:
> > http://www.sowa.synth.net/modular/addsr_punch.jpg
> >
> > Roman
> >
> > W dniu 2016-02-10 o 23:27, P Maddox pisze:
> >> Tom,
> >>
> >> On 06/02/2016 19:08, Tom Wiltshire wrote:
> >>> Being able to switch between the two curves would enable people to
> >>> use either a log or linear VCA and still get the same effect.
> >>>
> >>> What do you all think?
> >> That's what we do with 001/002/002R, you have the option for "linear" or
> >> "exponential" Envelopes.
> >> Exponential "sound" quicker than linear but give the typical "synth" sound.
> >>
> >> P
> >>
> >> _______________________________________________
> >> Synth-diy mailing list
> >> Synth-diy at dropmix.xs4all.nl
> >> http://dropmix.xs4all.nl/mailman/listinfo/synth-diy
> >>
> > _______________________________________________
> > Synth-diy mailing list
> > Synth-diy at dropmix.xs4all.nl
> > http://dropmix.xs4all.nl/mailman/listinfo/synth-diy
>
> _______________________________________________
> Synth-diy mailing list
> Synth-diy at dropmix.xs4all.nl
> http://dropmix.xs4all.nl/mailman/listinfo/synth-diy
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://synth-diy.org/pipermail/synth-diy/attachments/20160211/ac3740ce/attachment.htm>