I’m fairly certain that over the years I’ve read that Multi Band Compression is both “a miraculous savour of” and “an evil plague upon”, audio. Less dramatic commentators often suggest that it is something along the lines of “a useful and powerful tool that can nevertheless cause great damage ....” and various fora state unequivocally that “all mastering engineers” use them, and that “no serious ME would ever allow one in the studio” This is all very well and good, but you’ve probably got one anyway so what can you do with it?
Let’s take a look at the compressor function first, and let’s start with the single idea that probably makes the biggest difference of all. Even though the tool you have is called a “Multi Band Compressor”, try thinking of it as being several “Restricted Band Compressors” in a single box. Start off with all of the bands bypassed and then add one. If you need to compress the bass end of mix, add one low band, solo it (if you have that facility) and adjust the bandwidth or crossover points until it contains just the audio you require, then set the compressor functions as needed (assuming that you know your way around standard comp controls, if not leave the multiband beast alone and go figure them out).
If that’s all you need to do leave all the other bands bypassed and you have the job done. Obviously you need to undo the solo at some point (obviously – ahem). Google the infamous Andy Sneap C4 compressor setting for heavy guitar – this is exactly what he does. If you need to compress audio in another band then you can do that too, but consider it to be a different process that you just happen to be able to do in the same interface. Once you have done everything you needed to do, bypass the rest and leave it alone.
OK, so what about EQ? Well, if you have a 3 band MBC you can think of it as 3 band dynamic EQ, 4 band MBC = 4 band EQ (there’s a pattern here if you look carefully). Let’s say you have a piano part that gets a bit strident when the player gets carried away with the right hand in the chorus. You can EQ the offending frequencies to tame the sound, but then the part gets dulled all the time, even when it was sitting quite happily in the mix. You can automate EQ so that it pulls down the highs only on the loudest parts (this is highly effective but strewth it can sap your will to live) or you can apply an EQ that has effect only on the louder parts. Set your MBC so that any one of the bands contains only the offending frequency range, set the threshold to just catch the parts that are loud enough to be a problem, compress for gain reduction to taste and off you go. Again, bypass everything that you don’t use.
Once you’ve got your head around multi band compression have a think about what you could do with multi-band expansion!
Here’s just a few cool things you can do with a MBC
- Dial-in a dB or two of top end gain reduction when the signal is hot for an ad-hoc tape emulation.
- Set a high band to catch sibilance for an uber-controllable de-esser.
- Tame resonance (I find this particularly useful on strings and drum-kits).
- Push or pull a solo part in a mix (v useful for guitar solos when you don’t have the multitrack).
- Control prominent instrument transients in a mix.
I’ll say this again, if you don’t know how to use a standard (ie single band) compressor then don’t waste your time here, go practice and come back when you have that mastered.
Also note that MBCs do introduce phase shift to your signal; it’s usually not a problem but be aware that it is happening.
(Also also note that if you are using Waves C6 (which I like a lot) it doesn’t bypass properly, I queried what I was hearing with Waves support and their developers confirmed this behaviour).