Parallel compression is a great tool for engineers to use to enhance the sound of an instrument, or ‘fatten’ it up, without losing the important transients which give it attack and feel. Also known as ‘upward compression’ it brings up quieter sections and really beefs up the sound.
As a drummer I have often found that some recordings and mixes that I have worked on have lacked the sound I was wanting to achieve with the kit. This can be particularly noticeable with the snare drum which often loses most of the ghost strokes beneath everything else that’s going on. If I was to pile a compressor on the snare it would lose most of the attack from the initial transient. Parallel compression gets the best of both worlds.
If you bus the drum tracks (usually only kick, snare and toms to avoid unwanted ‘wash’ from the overheads when compressed) to an auxiliary channel and add thick compression to it you can then mix this sound in with the dry drum tracks. At this point I should point out that it is useful to send the outputs of all the individual drum tracks to a stereo auxiliary channel so that you are working with a single stem for the drums – stem mixing will feature in an upcoming blog. This simplifies the process by only having two auxiliary tracks to work with when blending the dry and wet signals, which should be mixed by ear. And when doing so the blended sound retains the attack and fast transients while also gaining some of the quieter sounds from the compressed track which give it a much larger sound.
To help explain in a practical sense I have found this great tutorial video detailing the process: