Audio Priority Switching Circuit. Can not find a schematic that will fit my need

I have searched but came up empty.
Here is the need.
2 audio lines coming in. 1 is on all the time. when audio is sensed on line 2, it will reduce (or turn off) line 1 allowing line 2 to take priority. Then when line 2 stops, (mobile radio traffic) it switches back to line 1.
The challenges:
Small as possible (and yet I can still solder together)
runs on 5-9V DC
Adjustable gain on inputs
Sensitivity adjustment on "switching" function

Of the hundreds of circuits I have looked at, It seems to be a fairly simple task with a FET ......  I can build it, but the design portion is a to much math for 
A 3 audio switching circut would be AWESOME!!!
Anyone seen anything out there that will help me in my search???


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dirtyoldm5 years ago
Look at the DG408 and DG409 analog multiplexers to do the switching.
I built an Atmel microprocessor controlled priority input for my stereo.
You can probably use simple logic.

I tried to use presence of a signal to switch the inputs.
But I had problems like quiet passages that required annoyingly long delays.
That forced me to sense power to each component, which works well.
Sadputter (author)  dirtyoldm5 years ago
Thats guys, I will check them out... Thanks for tqaking the time to answer!!
HOSER19615 years ago
I was looking for about the same thing. Hard time finding what I wanted, then I found this
Check it out.
What you are describing is sometimes known as "ducking". On an audio mixer, you can set two channels up in such a way that when a signal is received on one channel, the other is gained down by a certain amount. I would try searching that phrase, you should be able to find something that will work. It probably won't have some of the extra features afforded by mixers, including delay time and hold time, but I doubt those are necessary for your application
Sadputter (author)  SpaceShipOne5 years ago
Thanks for the reply. I have been chrecking the internet for ducking schematics / circuits to build. I can find them as part of a mixer but nothing stand alone.
I need something with a operating voltage of about 8 volts DC and is rather small. I just posted at TI to see if they have an IC that will start me in the right direction.
I have the need and ability to build it. There is this area called design that I am lacking... But learning....