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Do you mean coupling caps in the audio path, or caps across power and ground, near noisy ICs? (Then again, they're decoupling caps, I guess.)

For audio-path caps, I try to use film wherever possible. (Electrolytic is used in these applications due to physical size, not because of any superior audio properties.) For power decoupling, anything goes.

You're right, I had to be more specific. I've meant the coupling caps for audio-path.
So you use film for audio path? So if you have to use a 1uF cap you generally choose film instead of electrolytic? Is there a reason why film caps are better then  electrolytic for the audio path?

How about the power bypass caps? I generally use a 47uF and a 100nF (film), are these two caps (only) providing a good power filtering?

This topic has been probably discussed many many times, I've read many articles and posts on different forums so far and I think I've figured out some things the builder should check to remove (or at least reduce) the upsetting pop noise of the 3PDT switch; I'd like to have your opinion on this (maybe I'm completely wrong):

1) Switch quality:
I've done some tests with different 3pdt switches (purchased from Aliexpress, Tayda, Alpha, Hong) and I can clearly notice that cheap switch = loud noise.
Probably due to the following reasons:
- High force required to perform the switching
- Bad bouncing performance
- Bad Internal spring
The only exception is that I've found the Alpha 3pdt to make a louder pop than the Hong 3pdt (with the same circuit), but the Hong is supposed to be a clone (and even cheaper) clone of the Alpha.

2) Pulldown resistors:
The classic 1M pulldown resistor at the input is helping but it doesn't really cancel the noise. A pulldown at the output is also good. Grounding the input in bypass mode improve the noise reduction.

3) Bypass capacitors:
Any (even small) fluttering in the supply voltage could be displayed at the output of the circuit as a little parasitic voltage, that we hear as pop when the switch suddenly change its state. Is this correct?
This is something really interesting that I've not yet tested. In all my builds I've always used 2 sided PCB (with ground plane at the bottom and power plane at the top). I want to try now to assigning Vref (half of supply voltage) to the top plane and manually route the power lines (20 mil width) to let them be as short as possible AND placing the film box type bypass capacitor (not the electrolytic ones) as close as possible to the supply pin of the active components.
This way the inductance should be reduced at minimum and the power supply filtering should be improved.

4) Optical bypass
This is another thing I do want to test: the idea of never really mechanically disconnect the signal from the circuit input could be great, and could make the switching quieter (a mechanical movement is needed only at the output)


These are just some of the consideration I'm thinking of... what's your opinion?
Thank you! 

Hello everyone, this is my first post in this great forum.
I'd like to ask you what do you usually use for coupling capacitors. I've seen many builds using only polyester film type, and other using also electrolitic. 

Any advise on this?

ps: sorry for my english...