inSync reader Shawn E. in Tokyo wonders what a sidechain is, and how it is used – A sidechain (sometimes called a key input, or a detector input) is a control input used to trigger a compressor or gate with an external signal. Let’s look at a common example, ducking: When recording voice-overs, the background music bed is run through a compressor, which is set so that it is not normally operating on the input signal. The voice-over announcer’s mic signal is split so that it feeds both the mixer’s input, and a sidechain input on the compressor. When the announcer speaks, their voice goes to the sidechain, where it tells the compressor to start working, turning down the background music. When they stops speaking, the sidechain tells the compressor to stop working, and the music comes back to its uncompressed level. Other uses? Try using a kick drum to trigger a gated bass synth for extremely tight rhythms, or insert an EQ’d signal into a sidechain, making a compressor more or less sensitive to certain frequencies (de-essing is a good example of this), many other applications are possible – feel free to experiment!