[sdiy] Curious problem with VCA click
rburnett at richieburnett.co.uk
Tue Jun 1 17:58:58 CEST 2021
Do you only hear the clicking on the HP output when you're sweeping the cutoff frequency? Or do you still hear clicking even when the cutoff frequency and resonance of the filter are fixed?
Sent from my Xperia SP on O2
---- Benjamin Tremblay via Synth-diy wrote ----
>I have a circuit I built twice and both times I have this issue with a VCA produces a loud click (with with a slow-ish envelope attack) but only when I use a specific sound input.
>It uses a state variable filter I pulled almost verbatim from here: http://www.soundsemiconductor.com/downloads/AN701.pdf <http://www.soundsemiconductor.com/downloads/AN701.pdf>
>I am using the ALFA AS2164.
>From there I use the other 2 2164 stages to have a voltage-controlled mix of HP and LP.
>And from there I use the AS3360 VCA, one for a VCA and one for voltage-control of the filter resonance.
>Again, the VCA circuit is close to the reference implementation, with a quad op amp handling buffering.
>So, what’s the problem?
>The problem is consistently I hear the click on the VCA when I use the high-pass filter, which is bad because it’s for “high-hat” percussion sounds.
>If I route the low-pass filer into the 3360 VCA, it sounds great, even when I apply aggressive cutoff and resonance and crank up the mixer.
>Would a buffer or inverter fix this? Would a decoupling capacitor fix this (bias voltage) ? Or, is it very-high-frequency noise coming off the high-pass line (would passive filtering help?).
>The fact that this circuit consistently causes this problem has me scratching my shapeless, lumpy head.
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