[sdiy] clickless muting

[cheater cheater]

Hi David,

On Sun, Oct 28, 2012 at 9:44 PM, David G Dixon <dixon at mail.ubc.ca> wrote:
> Hey Team,
>
> Does anybody here have any insight into good ways to achieve "clickless"
> muting of audio signals?

The idea is to keep the frequency content of your gate below the
lowest frequency of your program. Otherwise you get clicks, due to
simple amplitude modulation arithmetics. For that purpose it's usually
a good idea to AC-couple the input to your muting circuit and set the
cutout time to be long enough. Naturally that won't mute treble-heavy
signals as quickly as it could. If you want insanely fast muting for
any sort of program, you perform a vocoding setup, where the program
is sliced into bands and each band is muted separately at its maximum
allowed "non-click" speed. This way, each band has a different decay
time.

Other than empirically testing, I am not sure how to go from frequency
content (i.e. "the gate should only have content under 20 Hz") to slew
rate. I think it might depend on device or at least device type. In
specific it must depend on the "knee", i.e. the shape of the
transition from the on stage to the release stage. Testing this
property might help select a good device.

D.

> My first inclination was to send a large (and
> slightly LPFed) positive voltage to a 2164 VCA (i.e., to use it as a
> switch), but I don't think that the 2164 VCA shuts off hard enough for true
> muting.
>
> Of course, the easiest way would be simply to put a toggle switch in the
> audio path.  However, I'm a bit concerned about feeding an audio signal
> through a panel switch.  (Am I right to be concerned about that, or is this
> a safe thing to do?)
>
> As usual, any and all help most appreciated!
>
> Cheers,
> Dave Dixon
>
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