A multiband compressor is a powerful tool for controlling dynamics.
The signal is split into three or more frequency ranges and processed independently. This is different from a standard compressor which operates on the entire frequency range at once.
Standard compressors are great, but sometimes you’ll find that with any significant amount of gain reduction you start to get a very dull sound. With multiband compression, each frequency range has an independent compressor so a source that has a lot of mid frequencies might end up with very little compression in the high frequencies, maintaining the brightness of the source.
Being able to apply different attack, release, ratio and makeup gain to low, mid and high frequencies gives enormous control. Unfortunately it can be tricky to set up it can do a lot of damage to the audio. It’s a tool you need to be extremely careful with. Used right, it can be much more transparent than a standard single-band compressor.
There are two ways that I approach multiband compression.
The first way is to use about the same amount of gain reduction for each band, by adjusting the threshold individually, and the second way is to use the same threshold for all bands and let the compressor take care of what is standing out.
There are many multiband compressor plugins on the market; for my examples I’m using the one included in Reaper ReaXcomp and comparing it to the standard compressor in ReaComp.
Example 1 – Drums
Here are drums with no compression: LISTEN
I set the single-band compressor to get a punchy sound. Attack and release at 10ms and ratio of 4:1. The threshold is set at -19 dB for about 3-6 dB of gain reduction, then 2 dB of makeup gain.
Here are drums with standard compression: LISTEN
In this example, you may have noticed some pumping. The compressor is squeezing down every time the kick hits. Using the highpass filter option in the compressor might help a little, but let’s see how the multiband compressor handles it. Using the same settings in the multiband compressor, each band is set to the same threshold of -19 dB. The overall gain reduction is about the same, the lows and mid frequencies each getting about 3 dB of GR, but the high band is barely doing anything.
Here are drums with multiband compression: LISTEN
To me that sounds more punchy without pumping. The snare has more snap and something cool has happened with the blend of the distant mics.
Example 2 – Guitars
Here are guitars with no compression: LISTEN
I’ve set up the single-band compressor to give me about 6 dB of compression at most, 25 ms attack and release, 4:1 ratio, and 3 dB of makeup gain. I’m pushing it pretty hard so that the compression is more obvious.
Here are guitars with standard compression: LISTEN
These guitars are pretty midrange heavy, and pushing that down with compression has made it sound slightly darker and there’s some pumping again. Overall, the frequency balance hasn’t changed too much, which is good. Using the multiband compressor should get rid of the pumping. With the same compressor settings copied into the multiband, there’s actually a little more gain reduction in the mid frequencies, nearly 7 dB. 3-4 dB in the lows and about half a dB in the highs.
Here are guitars with multiband compression: LISTEN
Dynamics are controlled, there are no artifacts, and the highs are nice and bright—what more could you ask for?
In these examples, were the dynamics destroyed? No. Did it sound unnatural? Not at all, the multiband approach was actually less damaging to the audio. No pumping, no artifacts, and no loss of top-end.
Multiband compression seems to be something that is either underused or completely overused. A lot of people say it’s only for when a track has serious problems or to be used only for mastering. I disagree. I use multiband compression whenever I’m not getting what I need from a single band compressor.
At the end of the day I don’t really care what tool you use, just as long as you’re getting the result you want. Don’t be afraid of multiband compression, don’t assume it’s overkill.
I learned a lot about using multiband compression from Ian Shepherd’s eBook Mastering with Multiband Compression, if you want to dig deeper into using them for mastering it’s definitely worth getting. I reviewed it here.
Jon Tidey is a producer/engineer who runs his own studio, EPIC Sounds, and enjoys writing about audio on his blog AudioGeekZine.com.
