Sidechaining compression is a very powerful tool that allows the user to control the dynamics of a source. This technique adds space, rhythm, energy, and separation to a mix, and it involves threshold, ratio, attack, and release times. When using sidechain, the user can tell the compressor to monitor and control the level and volume of a different channel or instrument. It’s worth mentioning that when the sidechain gets louder, the compression holds down on the channel that it is applied to. 

Sidechaining is capable of bringing out vocals to make sure the voice of the singer is heard over all the backing tracks. Sidechaining is also capable of isolating specific frequencies through a multiband compressor, though it is not recommended to apply the sidechain effect to an entire track. 

Sidechain compressors are typically used via software plugins or presets on different tracks. Producers and musicians apply sidechain effects in a different way. Some users run two different forms of sidechain compression on the same mix.

As a final note, it’s worth mentioning that sidechain is not necessary, but it is quite helpful. Sidechain gives the kick/snare a little more room, so when sidechaining specific frequencies of a sound, one sound drops as another one arrives. Many professional producers don’t seem to use sidechain quite often, since, with proper equalization, sidechain is not really necessary.