Audio ducking is the process of reducing a channel of audio when another channel of audio appears. This process is used in many retail stores where background music is being played thru a public address system and when one talks into a microphone, the background music is either reduced or eliminated all together. Once the talking ceases, the music comes back up either quickly or slowly depending how it is configured. This is what is called "ducking".
Ducking is accomplished in a few ways. The simplest is a switcher that when the microphone button is pressed, the background music is cut off hard. Letting go of the button returns the background music. A more sophisticated and more pleasing sound is an audio detection circuit that senses the mic audio and fades the music down quickly and when silence is detected, the music slowly fades back up. Adjustments would be the sensitivity of the mic audio cutting the background music, the speed of the fade and the speed of the returned audio. This can all be controlled by three controls.
As time permits I will publish both a simple relay type switcher and a smooth electronic ducker that is more desireable.