"capacitively coupled noise"

[smnm]

Came across this in RG's article "The Ins and Outs of Effect Bypassing" at geofex:

"The version of true bypass with the DPDT that leaves an extra throw to which the input of the effect is connected when the effect is bypassed has been used in some pedals to good advantage to ground the input of high gain distortion effects, which produces some decrease in capacitively coupled noise."

Can anyone explain what this is, or what it sounds like?

I'm curious as I started off using this bypass but switched to the easier one seen on Dragonfly's vero layouts and elsewhere some time ago.

[Paul Marossy]

I think I'll let others more qualified than myself answer the capacitively coupled part, but I can tell you than on really high gain circuits, it's a good idea to use the grounded circuit input true bypass scheme. If you don't, your circuit can oscillate when in bypass mode. And that can somehow end up in your bypassed effect as a faint, relatively high pitched whining noise in the background. It's happened to me on a couple of occassions. 

[smnm]

ok, yeah, thanks Paul - I've heard references to 'whining' in pedals here and there, now I know what that's about. I don't think I've heard it but I think I used the grounded input bypass on my Parallel Universe and Uglyface builds...

[brett]

Hi.
The capacitatively coupled noise thing is reasonably easy to explain.
There are many parts of the signal paths of our pedals where we pass the signal across a capacitor.  Although we don't often think of it, the signal is being passed across an INSULATOR.  Maybe the physical gap between the end of one "wire" and the start of another is only a few thousandths of a mm, but there is ALWAYS a gap.  As well as the innards of caps, air and empty space are good enough transmitters of electrical fields to slightly couple all wires together (a little bit). 

If we make a high-gain pedal, with long input wire (antenna for electrical fields) and high input resistance, the input wire might become well coupled to the output.  The faintest disturbance will make the whole thing oscillate. 

Fortunately, grounding the input while the circuit is not in use makes any capacitatively coupled input flow harmlessly to ground.
cheers

[smnm]

Thanks