MixTips #3 – Parallel Compression
Just because you failed high school trigonometry doesn’t mean you can’t use and profit from parallel compression in your mixes. Parallel or “upwards” compression is simply the process of combining an un-compressed signal with a compressed-one and blending to taste. This ‘best of both worlds’ approach is designed to preserve the dynamics, openness, punch, character and frequency response of the un-processed signal while solving the issue of the overly dynamic track getting lost in the mix or sound thin/weak.
While many newer dynamics plug-ins feature a built in “wet/dry” mix parameter that allows inline parallel compression tricks, you can easily achieve this effect with any compressor/limiter. Basically we are going to duplicate the track we want to compress, add a lot of compression to the duplicate and blend with the original to taste. Essentially what this is doing is creating a dense ‘bed’ of sorts for the uncompressed track to ride on, preserving all the original dynamics while allowing the track to sit comfortably in the mix. This trick can be used in subtle or extreme ways and works well on almost any source material, especially where transparent and natural sounding dynamics control is desired.
Parallel Compression Tips:
Drum Squash: Create a aux return with an aggressive compressor or limiter on its insert, you can call this “Squash Bus.” Using sends, send all your drum tracks accept the kick drum to this squash track and blend with the original (dry) drums to taste. Leaving the kick drum out prevents the squash track from over-reacting to the dynamics of the kick, which tends to dominate the other drums. You can experiment with including the kick to create cool pumping effects on the squash track. Try EQing this squash track in different ways, or even add distortion for an over-the-top effect.
Automation: Automate your parallel track up and down at different sections of the song, bring it in during the choruses for more power and support, bring it down during the verses for a more intimate feel.
Using a Limiter: For natural dynamics control on vocals, guitars, etc. try using a very fast (brickwall style) limiter on the uncompressed track just to keep the peaks under control so nothing jumps out of the speakers (you know, in that uncontrolled, “karaoke” sounding way). Then use the parallel track to subtly bring up the valleys and fill in the body/sustain of the track. This works really well on vocals with a ton of plosives (e.g. hard P or T sounds) that you don’t want to over compress. The brick wall limiter will transparently grab and control those plosives transients while the parallel track will bring up and support any softer sections without having to squash the crap out of the vocal.
Compensate for any delay to maintain phase coherency: Because some compressors/limiters incur a small amount of processing delay (usually do to look-ahead algorithms) it is important that each component of the parallel chain is delayed by the same amount. For instance, if you were to create a duplicate track of a vocal and apply a L1 Maximizer to the duplicate (parallel) track, there would be a noticeable latency and serious comb filtering would be heard when both tracks are played together. Most DAWs (except for Pro Tools) handle this automatically as part of their built in PDC (plug-in delay compensation) engine. In Pro Tools LE/Mpowered, the easiest way to solve this is to copy the plug-in to the original “dry” track and bypass it, thereby incurring the same delay on each track. A more permanent solution would be to shift the duplicate track backwards by the amount of delay the plug-in is causing. In Pro Tools HD you should always use delay compensation when mixing/editing. Remember, not all plug-ins incur a delay, in fact many do not, so considering using those when creating parallel chains.