does this exist?

[lefthanddoes]

You know what would be sweet? A manual-noise-gate-button. It would be an analog device with input and output, and just a single, spring-loaded button. When the button isn't being pressed, the signal is being silenced. As the button gets pressed, the volume gets gradually brought up to 0, and so when the button is being pressed fully in, the signal goes straight through unprocessed.
So, if you know the rhythm of say, a bass part or vocal part, you could run the signal through this button, and press the button in rhythm as if you are "playing" the track. The gradual volume change would act like an attack or release time control on a traditional noise gate, eliminating clicks or pops and allowing you to chase sustained notes.

I guess you could just do this with a fader, but you might break it.

What kind of electronics would be involved in this kind of project?

[Scodiddly]

Pretty much any synth that lets you use an external signal. Mostly that's modular synth territory, but there are some other units that will do that. Or you could just buy an ADSR module and an amp module and slap together a simple trigger button.

[CurtZHP]

Find a cheap noise gate pedal and replace the latching bypass switch with a momentary?

[Boogdish]

If you're dealing with unbalanced connections you could do this really, really simply. All you need is a momentary SPDT (or a DPDT and just use half) switch, two jacks and some wire.

Wire the tip connector of the output jack to the center lug of the switch.
Wire the tip connector of the input jack to the normally off lug of the switch.
Wire the sleeve connectors of the jacks to each other and then to the remaining lug of the switch.

If you wanted to get fancy, you could even put a large resistor (1meg) from the tip connector to sleeve connector of the output jack to de-bounce the switch.

If this seems too complicated for you, I'd be happy to build you one for cheap.

[eeldip]

synth into a sidechain?

[lefthanddoes]

Thanks for the replies, folks. Seems like synth into sidechain would probably do it. Also, Boogdish, that device seems simple enough to build. I don't understand about the resistor though, what would that do? I don't know what the de-bouncing is all about. Does that have anything to do with allowing the signal to engage and disengage gradually (or at least gradually enough to eliminate clicking/popping)?

[casey campbell]

a gate with a key?

[lefthanddoes]

Well now we have two solutions involving keys. Run the track into a synth and key it with the synth, or run the signal into a keyed noise gate and key it with some kind of trigger, like say... a simple synth...

[The Scum]

Synth modules might seem to be indicated.

You posted this in the DIY forum, so I'm assuming you're looking for a DIY solution?

A VCA module, an AR (or ADSR) envelope, and a button to generate a gate are indicated. You can find schematics all over the web for these...Rene Schmitz has some designs for inexpensive VCAs and ADSRs with garden variety parts:

http://www.uni-bonn.de/~uzs159/

There are many ways to skin this cat.

One alternative would be to use series/shunt optocouplers. They have an intrinsic on/off delay that will give you clickless operation:

http://www.silonex.com/audiohm/softswitch.html

There are some chips that include an audio VCA among other functions: like the National LM1036. You can drive it with some control voltages for VC level, panning and tone controls.

http://www.national.com/mpf/LM/LM1036.html#Overview
http://www.mindspring.com/~clist/resour ... Mixer.html

[Boogdish]

The 1M resistor is there just to keep from having an open circuit in the tiny little moments while the switch is between contacts.

I don't think this would sound as good as a VCA because it wouldn't be gradual at all, but I wanted to present the absolute simplest solution to the problem.