[sdiy] Mute solution?

Mattias Rickardsson mr at analogue.org
Sat May 26 11:16:07 CEST 2018

Muting with the series/shunt FET solution as described by Douglas Self is
probably superior to the simpler Boss pedal solution when there is need to
shut off the entire audio range, so be sure to check it out. I was dabbling
with it yesterday, trying out alternative JFETs as the BSR57 is suddenly
out of stock globally.

Switching at zero crossings still gives a discontinuous derivative, so it's
like having the clicks 1-pole low-pass filtered - not removed. Often they
will still be heard, especially for purely low- or mid-frequent material
without many overtones, so it had better be tested in a particular
application before trusted as a click-free solution.

That said... how is it done in existing "clickless" switch ICs? I guess
it's just switching at zero crossings, or are they fading the signal in
some way?

It's still probably seen as "good enough" in some high-end designs, for
instance Zähl writes:
"click-free audio switching using zero cross detection on parameters
relevant when mixing live"

A short fade-in/out is often mentioned as the better solution, but the long
fade times needed for bass tones are unnecessarily long for high
frequencies. Also, depending on the product or use case, a fade can be a
very problematic solution if, say, a channel is supposed to be switched on
for just a particular time slot for a drum sound or similar sudden events.
If you don't switch it on "too early", you'll miss the attack of the sound.
If you switch it on early enough, you also get some of the unwanted sound
preceding the wanted sound. And the same problem applies to the end of the
time slot. Btw, the same problems arise when using multiplexed & filtered
CVs to feed VCAs - they don't shut on/off instantly. In a drum machine or
multi-timbral synth or automated mixing in general this can be a real pain
in the bass.


On 26 May 2018 at 10:27, Andre Majorel <aym-htnys at teaser.fr> wrote:

> On 2018-05-24 20:47 +0200, Roman wrote:
> > How about detecting zero-zrossing and shutting down the audio
> > with clamping MOSFET or whatever when signal is no more than
> > 1mV away from GND? No clicking.
> If you want to hear what switching at zero-crossings sounds
> like, play the WAV file at
> http://www.teaser.fr/~amajorel/gatedsine/
> The signal being switched is a low-frequency sine so as not to
> mask the artefact. On a signal with more high frequency content,
> the artefact would be less conspicuous.
> --
> André Majorel http://www.teaser.fr/~amajorel/
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> Synth-diy mailing list
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