[sdiy] Chris Synths polysynth

[Mike Bryant]

If you change the PWM mark/space ratio, it doesn't instantaneously change the voltage on the capacitor to the new value - that takes several time constants of the RC smoothing filter.  In fact of course it never gets to the exact value but close enough for most purposes after the delays mentioned.

-----Original Message-----
From: Synth-diy [mailto:synth-diy-bounces at synth-diy.org] On Behalf Of cheater cheater via Synth-diy
Sent: 23 October 2021 14:59
To: Martin Klang
Cc: synth-diy
Subject: Re: [sdiy] Chris Synths polysynth

I don't understand, why does the delay happen? Thanks.

On Fri, Oct 22, 2021 at 2:56 PM Martin Klang <mars at pingdynasty.com> wrote:
>
> Ah that explains the big slew. It's a very annoying thing about the 
> KeyStep that the CV output only settles some 6-8mS after the gate. IMO 
> they should have delayed the gate to coincide with the CV.
>
> For many things, like controlling an analog synth directly, it doesn't 
> make a lot of difference since a few mS of frequency slew isn't 
> audible (to my ears). But if, say, you are making a CV to MIDI 
> converter and want it to be compatible with what's probably the most 
> popular CV keyboard on the market, then you have to add your own delay, and latency.
>
> And yes I know, you could just use the MIDI output of the KeyStep 
> directly, but that's not the point!
>
> Thank you Vladimir for this nugget of information -
>
>
> Martin
>
>
> On 22/10/2021 12:15, Vladimir Pantelic via Synth-diy wrote:
> > Arturia uses a dual PWM scheme in all of the their Keystep and 
> > Beatstep products, basically following the circuit laid out here:
> >
> > http://www.openmusiclabs.com/learning/digital/pwm-dac/dual-pwm-circu
> > its/index.html
> >
> >
> > it works nicely, BUT also introduces a >4ms slew on all CV outputs, 
> > no biggie if driving an analog synth and it gets hidden in the 
> > attack, but a real nuisance if it gets sampled by a digital module...
> >
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