Need circuit design...

hi all,, I am in need of either a supplier or a circuit design for the talkover function on an audio mixer... let me explain.... what i need is a variable dipping control.. which has two audio inputs and when one becomes live ie music.. the other one (which is playing) gets faded out.. and when finished the first channel returns to original volume... the rate in which it retracts and returns would like to be controllable too.. I was using an old mixer which had a threshold and depth controls with the depth turned right up I could knock out the backround music while the mic/second input played...

if anyone would know of the design or possibly an exsiting stand alone unit this would be very very helpfull...

thanks


solution...

Don't you use a compressor with a sidechain for this? You could easily buy a ready made unit if that is the case.