Silent Audio Switching

T Chap

To swicth a a Hi-z input and retain straight wire I am going to use relays. I want to add a shunt to ground to trip prior to the relay to avoid contact noise. Ideally, a ramping up or down would be best to fade the audio over a few ms. (RC and FET?) Any suggestions on a circuit to accomplish this idea? The processor will either be a Propeller or SX. The shunt would have to be very quite also. It would short the input to GND prior to connecting/disconnecting the relay.


Thanks for any ideas.

Chris Savage

Hello,
·
·· If you have fairly clean Relay contacts and your audio inputs are capacitively coupled you shouldn’t really have a lot of noise.· There are Integrated Circuits for switching audio as well.· Many have an I₂C or SPI bus control, while some are parallel.

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Chris Savage
Parallax Tech Support

matthelm

How about the 4066 or one of it's relitives? Only bad thing is you need a P/S that has a larger range than the signal.

mediaprefect

If you are going to use a CMOS switch or perhaps a Intersil DG444, you can eliminate switching pops by carefully putting a small DC bias on all of the audio lines and switch inputs. Watch how you couple sections of your circuit. Don't pull your input to ground, connect it to the DC bias source instead. I have seen this method used a number of times in commercial (broadcast not consumer) products and it always seems to work quite well. Read Intersil's AN1034 found here: http://www.intersil.com/data/an/an1034.pdf. It will probably answer most of your questions.

Rick