[sdiy] Blackmer VCA cell

[Mike Bryant]

Yes I've noticed that 'being held constant' effect on my pure digital synths even when being able to ramp between linear and exponential.  I did once try a two part Attack but it just made things more complicated for little gain.

But I'm going to try adding the 'hyper-convex' curve Mark Verbos suggested to my control later on and see if this improves things.





[cid:image001.png at 01D7C9BB.2ACD1670]



-----Original Message-----
From: Synth-diy [mailto:synth-diy-bounces at synth-diy.org] On Behalf Of Richie Burnett
Sent: 25 October 2021 15:33
To: synth-diy at synth-diy.org; Gordonjcp
Subject: Re: [sdiy] Blackmer VCA cell



Totally agree Gordon. I was just about to say that several synths with digitally generated envelopes have a linear attack phase.



The rate of change of an exponential attack becomes so small towards the end when you approach the target level, that it's hard to perceive any change and it just sounds like the level is being held constant for some time before the decay phase kicks in.



-Richie,





---- Gordonjcp wrote ----



>On Mon, Oct 25, 2021 at 09:18:30AM -0400, mskala at northcoastsynthesis.com<mailto:mskala at northcoastsynthesis.com> wrote:

>> On Mon, 25 Oct 2021, Gordonjcp wrote:

>> > On Sat, Oct 23, 2021 at 06:18:37PM -0400, Matthew Skala via Synth-diy wrote:

>> > > A capacitor charging from a voltage source through a resistor

>> > > will change its voltage fast at first, when there's a large drop

>> > > across the resistor and therefore a large current, and then

>> > > slower as it approaches the target

>>

>> > It's a little more complicated than that because in a "real"

>> > envelope you have the timing cap charged off the full positive rail

>> > (either 12V or 15V) but the comparator that flips to the decay phase set for 10V.

>>

>> What I wrote is true - it's faster at the start and slower toward the end.

>> The fact that the voltage source used for charging is beyond the

>> target voltage does make the difference between the start and end

>> smaller; it's less concave down, and closer to linear, than it would

>> be with a voltage source nearer the target voltage.  With the voltage

>> source exactly at the

>

>Right, but the "shinty stick" part of the the exponential charging curve is very much lopped off by stopping charging at 10V.  When you do that, then the attack portion is audibly indistinguishable from linear.  Indeed, the Juno 106 which has famously punchy envelopes uses a totally linear attack phase and expo decay and release.

>

>--

>Gordonjcp

>

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