Available as an assembled Module and as a DIY project.
This Module is currently available.
Side chain module
Freestyle High Fidelity Ducking Circuit
Ducking is also called sidechain compression. This effect is most commonly found in electronic music, where when the kick drum hits, the rest of the music is reduced in volume.
This circuit will get you there! In high-fidelity! Because most analog VCAs use chips which introduce distortion and noise, and this circuit uses a low-noise audio op amp and a photocell as a variable shunt resistor, which is very low-distortion and noise.