We do something along those lines in avionics, but it turned out to be less
>than useful. We called it priority encoding. That is, you have a number of
>inputs (say 4 for example). You put the most important signal on channel 1
>and you use a simple diode detector to see if there is any audio on this
>channel. IF so, THEN shut off the other 3 channels with gates and the usual
>audio analog switch like a 4016. Then IF no audio on 1, then the second
>priority line uses the same detector and IF audio on this channel, THEN shut
>off 3 and 4. And so on down the line. 4 needs no detector. If there is
>nothing on 1, 2, or 3, then 4 is a pass-through.
>
>The problem we found in actual service is that you'd be listening to
>something rather important on line 2 when line 1 came on calling another
>aircraft and shut off #2. Not a good thing. I think I've got the prototype
>around in the "that was a hell of a good idea" box somewhere.
>
>Jim
I would use a stereo headset. Feed both channels normally. Then put #1 to one side only then put other channel on other side, with ability to manually control.
greg