Multiband Compression Workshop

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The Do’s And Don’ts of Multiband Compression
Compression (sigh), what an annoying signal processor. Other signal processors are so straightforward. EQ, you pick a frequency, pick a bandwidth, and you boost or cut. Simple. Delay, you pick a time setting and feedback, and look, echoes. Nice. Compression… not so much. Every control effects every other control, with moving parts, and it’s all so signal dependent. You can set a compressor two completely different ways and get very similar results, or, set the compressor and change one control and get a totally opposite effect. Now, couple all of that complexity with having control over individual frequency bands and you get the fire-breathing minotaur that is Multiband Compression.
To help guide your path, I’ve put together a little list of “Do’s” and “Don’ts” when it comes to multiband compressing…. err… compressing multibandingly… no… … you get it.
DON’T use multi band where regular EQ or compression would suffice. Multiband compression gets a reputation for being some mythical magical secret sauce in a mix; but that’s only because people don’t understand how to use it. It’s just a tool like anything else and for most applications regular ol’ EQ and compression will not only suffice, but typically sound better. If I were to put a #1 mistake label on any mistake people make with multi band compression - it’s overusing it. This is extra extra true when it comes to your mixbus. YES - MB Comp has a place there sometimes, but most of the time what we want can be better achieved through other means.
DO be specific about your intentions when pulling up the MBC. Why are we using it? Is it because we want to control the upper midrange on a vocalist who keeps tensing their neck when they move up in pitch? Is it because we want to thicken up the fundamental body of a bass guitar while keeping all of our finger sounds and attack tones nice and dynamic? Is it because the acoustic guitar player was swaying back and forth while playing their part and the alignment of the mic with the sound hole keeps changing so we keep getting random bass build up?? Specific intention means we are listening and reacting to the music at hand. It also means we can set our crossover bands accurately by soloing and isolating exactly what we want to hear within the band range.
DON’T be overly aggressive with timing constants. Remember two blurbs ago when I mentioned that a regular compressor is often better for a job? This is especially true when it comes to stuff that requires fast reaction times from the compressor. Put an EQ on any sources, set a bell curve, and quickly turn the knob between boost and cut. You will hear audible phase distortion, almost like a phaser if you do it aggressively enough. That’s what your multi band is doing. Smearing them transients all day, causing weirdo ripples across your whole frequency spectrum. This effect is mitigated the more gradually your tone is shifting. Now, sometimes distortion is our friend. A lot of Hip Hop vocals are hit with the tried-and-true Waves C4 “Pop Vocal” preset, and I’m not gonna lie, I actually like the sound. It’s grainy, and a little 2d, but it’s kinda cool. But make sure that if you’re getting that effect, it’s because you specifically want it.
DO embrace experimentation. While I’ve just laid out three precautionary little tips, it’s also worth mentioning that being aggressive with multi band compression can produce some interesting results. In fact, there’s a compressor called OTT (which stands for Over The Top) that is entirely based on going way too far with multi band comp and it’s a pretty durn cool little effect. There’s some very cool effects that can come from messing with MB.
Some bonus tips:
Vocals - The low mids of a vocal are very tricky. This is where all the body of the voice resides, but it’s also where all the mud and room tone hangs out too. MBC can be a great tool for controlling the mud while preserving the body. Set your band to isolate the 250-700Hz (ish) range, with a gentle crossover slope if the option is available, and use soft-knee, slow attack, medium-fast release compression to keep the quantity of low mid energy consistent. You may need a little make up gain within the band to get some body back after doing this.
Cymbals/Drum Kit - Sometimes you get that perfect drum sound, but every now and then the drummer hits a cymbal a little too hard and you either get a bit too much treble or a bit too much upper mid. Target your harsh frequency range and set the threshold pretty high - you only want the compressor working when the cymbals actually get too much action. Use a fairly fast attack and medium-ish release to smooth out those overly aggressive moments.
Bass Guitar and Kick - Ducking the bass from the kick is a fairly common technique in genres like EDM and Pop. If this term is new to you: ducking is when you put a compressor on one element, but you trigger the compressor with another element. In this case, the compressor is on the bass, but it’s trigger when the kick hits. This allows the one element to temporarily “get out of the way” of the other. The thing is, it doesn’t work so well in records that use live bass because it tends to disrupt the groove. However, with multi band we can set it up so that only the lowest frequencies of the bass guitar duck the kick - while all the mid tones remain unchanged. This allows us to retain some sense of the dynamics of the bass guitar while also allowing the lows of the kick to poke through. Like having your cake and ducking it too.
808s - Sometimes we want to be clean and pristine with our sounds. But… sometimes we don’t. 808s thrive on distortion. The distortion characteristics of an 808 tend to live in the same range as the attack of the 808 - so if we boost all those grungy tones we may end up making the 808 a little too punchy. MBC can give us the green light to really boost this crud out of the funky stuff, while at the same time giving us the ability to attenuate the attack in the same range. Here, we’re gonna want to use fast attack and fairly fast release settings to attenuate a healthy amount of punch - and then a whole punch of make up gain on the band to boost things up. The net result should be the attack of the 808 staying in place, but all the sustain (the distortion in the body of the 808) coming way up in level.
So that's how I view Multiband Compression, but like all things in music the choices are subjective. How are you using Multiband? Let us know in the comments!
-Matthew Weiss