The Thought Process Behind Multiband Dynamics

Multiband Dynamics, which often take the form of Multiband Compression is a very powerful method of signal processing, but I feel that a lot of people don’t quite recognise the time and the place for it!

Firstly, I would suggest that there is perhaps no wrong place for it, and I would encourage all readers to try to use it in any instance where they might reach for an Equaliser (EQ). What you will find is that Multiband Compression can sometimes fill the shoes of an EQ, and by reaching for it more often, you will get a feel for what it’s good for and what, potentially, it’s not.

For those asking the question ‘what is it?’, what is it?

Multiband Compression is dynamic range compression, but with the added ability to treat only a single frequency band, or multiple frequency bands with different gain reductions, different thresholds, different attack and release etc. For example, it could compress everything below 1000 Hz but leave everything above it alone. Or it could compress the bass range with a high ratio, but the treble range with a low ratio.

What I want to focus on in this article is the thought process behind choosing this as a tool.

The main thing that goes through my head when considering multiband compression is, is there an area of the spectrum that blooms too much on some notes, but is ok on other notes? An example might be a synth that has a good balanced spectrum when playing in the mid range, but when they go down to the low notes, the bass wobbles out of control a little bit too much. That is a prime use-case for MBC (Multiband Compression).

Why the above example would benefit from MBC more than EQ is that EQ is a blunt tool, which will reduce the low end energy regardless of whether the synth part is playing higher notes or lower notes. This might leave the higher notes feeling thin and brittle. MBC can engage only for the lower notes taming them but leaving the higher notes almost unaffected.

Pictured below is the FabFilter Multiband Compressor, but of course, any similar product will do! 

In this image, only the low end will be affected and these settings are useful, as mentioned, for instruments that are balanced when playing higher notes, but bloom uncomfortably when playing lower notes.

Taking it a step further, is this next image:

In this example, we are boosting the same bands that we are compressing. My thought process when considering this technique is this:

I want to boost these frequencies, but if it gets out of hand, I want it not boost so much

And this is basically what we get. These bands will have gain applied to it, but that gain will be reduced if the amount of signal in that band exceeds a certain threshold.

Lastly, consider this next image:

The thought process behind this would be something like: I want the midrange to be generally hotter, but if the instrument plays notes that already aggravate that range, I want it to push it back into control.

An example of this might be lead instruments, a midrange boost like this can give them a lot of power, but then if the instrument goes up into a higher register, this range can start to peak quite a bit. In this situation, set the threshold on this range such that the higher notes duck this band, but when playing lower notes, it ducks only a little bit or not at all.

In this article I’ve purposefully tried to be vague in terms of numbers. This is because I believe the key to using these things well is the thought process behind choosing when to use them in the first place.

In this article I’ve given 3 use cases, and these use cases are ones that come up quite commonly. Give them a go and hopefully you’ll get a feel for the when and the where of Multiband Compression. Lastly, as I mentioned at the outset, I would strongly recommend trying to use Multiband Compression at any moment where you might otherwise reach for an Equaliser. It might not always give you the result that you are after but it will definitely give you a sense of what can be accomplished using MBC and how the results can be quite different to other signal processing tools.