In this article Julian considers the merits of the multiband compressor. How much do we use them and when we do, what for?
Inspired by a discussion about Paul Maunder’s excellent article on using FabFilter’s Pro MB in Post Production in which Paul uses a multiband compressor as a more forgiving alternative to a full band ducker when balancing a Voiceover over a music bed, the team were discussing their use of Multiband compressors. The consensus on the team was that we really didn’t use them much. I was surprised as I had always assumed I was something of an outlier in using multi band compression as little as I do. This prompted me to check more widely as I consulted our team of regular contributors and the trend persisted. Multiband compressors might be common but they don’t seem to be used as much as you might think.
Before going any further we might take a minute to examine the multiband compressor. What is it and why was it developed?
Why Multiband?
Applying a treatment to a specific area of the frequency spectrum can be extremely useful. Think of the relationship between volume and EQ. We can use a fader to turn a track up or down. But by using a band of an equaliser we can adjust the level of only part of the spectrum, giving us more control.
The example of adjusting a fader is simple. The character of the audio is unaffected by a volume adjustment. It’s just louder or quieter. The same can’t be said of all processes and an excellent example is compression.
Single band compression (i.e. regular compression) attenuates the entire frequency spectrum when the audio reaching the detector exceeds the threshold. The familiar issue of a kick drum or other bass heavy signal causing the rest of the audio to dip as a compressor does its work is part of the sound of contemporary music. However it places a limit on how much a compressor can respond to other elements of the audio if its action is being dominated by one aspect of the music, for example the kick drum.
Filters in the detector side-chain are an excellent way to control exactly what the compressor responds to, but a compressor used in this way is still a single band of compression. And what happens in one area also affects the rest of the spectrum. The only way to isolate the action of a compressor between different areas of the spectrum is to have an individual compressor for each area to be processed - A multi-band compressor.
Multiband Compressors
By dividing the audio spectrum into separate bands, typically three to five, a multiband compressor can selectively compress specific frequency ranges, addressing issues like excessive dynamic range or tonal imbalances. The controls per band are much the same as those found on a regular compressor but the complexity rises exponentially with each band available and it is for this reason that they have the reputation they do as tools which can achieve results which would be difficult using conventional tools, but the chance of doing more harm than good is high. To someone who doesn’t have a thorough understanding and experience of single band compression, a multi band compressor is a dangerous thing.
I find multi band compressors reward clarity of purpose. If you know what you want to achieve, and a multi band compressor is a good way to achieve it, then things are likely to go well. However pulling the controls around to see what you get is likely to do more harm than good. They are surgical tools, and much like actual surgery they are a case where I’d rather avoid aimless experimentation!
For this reason the times I tend to use multi band compression are rather specific. I find they can be excellent for introducing fizz and excitement into vocals, succeeding where EQ doesn’t deliver the same results. I also find them useful with just a single low-end band active to control the bottom end on busses.
User Interface
Multiband compressors are somewhere the user interface really makes a difference. FabFilter are always commended in this area. I really like the sound of McDSPs ML4000, but I’m not a fan of its very busy UI. However a UI I’ve found I get on with very well bucks the trend when it comes to super-modern interfaces with rich visual feedback. I like Softube’s Drawmer 1973, the fully featured version of the excellent preset-only S73. Maybe it’s the skeuomorphic design which forces you to listen which means I find I can use this without getting in to too much trouble!
What Are You Using Multiband Compressors For?
A multiband compressor is a complex and flexible beast. The most complex can function as anything from a full band compressor, to a crossover/signal splitter, to a dynamic EQ, to a multi band expander and many other things besides. They cross over significantly with dynamic EQs and I discussed the difference between a multi band compressor and a dynamic EQ in this article. A great example of a video which really illustrates the benefits of a multi band compressor from Avid’s Simon Sherbourne is included below. The usefulness of multi band compressors on complex signals is nicely demonstrated here and the reasons for the popularity of multi band compression and expansion on stems in Post Production and across mixes in both post and music is clear. Although its a promo video for a specific product its definitely worth a watch.
What Did The Team Say?
Below are some highlights of the comments of some of our contributors, from both Post and Music on their use of Multiband compression:
Eli Krantzberg
I occasionally use them on my mix bus. I’ll put iZotope’s Tonal Balance on my final output with a custom target curve. And then I’ll sometimes use the multiband compressor on the mix bus to help in frequency areas where my mix is off from the target curve. I find it subtler than simple EQ. I can use the threshold and makeup gain (and even the attack and release, although less so) to just nudge it gently toward the target level I want. I think of it as central bankers adjusting interest rates to control inflation. It's a blunt tool that merely lightly nudges things in a certain direction rather than yielding 1:1 results.
Russ Hughes
Good for ducking music beds with a sidechain when using dialogue - as Paul Maunder showed in his recent video.
James Richmond
Fairly often for taking the harshness out of overheads, to make room for vocals in busy arrangements, on drum loops to enhance certain elements (kick/snare or everything other than kick/snare), on distorted bass, on bass drum to bring out the click or the boom more.
I tend to have unused bands in bypass, but it really depends on the source.
I often used to put McDSP ML8000 on the master bus but have moved away from that lately- it is more of a limiter anyway.
Steve DeMott
Not often, in music projects, but sometimes to handle specific problems. I typically use the Metric Halo (really clean & transparent) or McDSP (if i want color/vibe), but have been finding the Avid Pro Multiband to be really nice lately as I’ve been more conscious of using plugins that are more universal, so my assistant can use my templates.
I did steal an idea from Gary Bourgeois, using a multiband on dialogue tracks. That is the only place I do use one consistently. Again moving from the Metric Halo to the Avid Pro.
Graham Kirkman
Virtually never
Rob Walker
I prefer Fabfilter Pro Q in dynamic EQ mode if I need frequency specific dynamics. Whenever I’ve tried to get something useful with a multiband I end up hearing issues in the crossover points. I used to use Waves C4 but as an expander for noise reduction when options for that were limited.
Nathaniel Reichman
I use Avid Pro Multiband for the music ducker trick, but only on certain bands. I turn off the lowest one at least. But I use DMG Multiplicity even more- sometimes in the way some people use dynamic EQ, but also as a multiband de-esser. I love how deep Multiplicity is.
Roger Guérin
I also use Avid’s Pro Multiband on every stem… just in case. Compressing in a particular frequency range without affecting other frequencies is always beneficial.
Do you use multiband compressors much? What do you use them for when you do? Share your comments below.