A Crash Course in Multiband Compression - Part 1

A Crash Course in Multiband Compression - Part 1

Today I want to provide tips on when and why we may use multiband compression, as well as highlighting a few practical scenario’s of when to use this technique on your productions, mixes & masters.

Compression is such an integral part of the music making process. It’s often what makes or breaks a good mix, helping to “glue together” the elements in a song, as well as help with getting that “punchy” sound we know and love.

Multiband compression is a tad more sophisticated than your traditional compressor, though it still behaves in the same way. Therefore when used too much, or when not used appropriately, the results it yields could be detrimental to a good sound!

Ok let’s start with Compression 101:

Think of a compressor as an automated fader assistant. Every time a signal exceeds a specified volume - as set by the Threshold - the compressor acts by reducing that level. The amount in which it reduces depends on the Ratio.

e.g. with a Ratio set at 2:1, every time our input level exceeds our Threshold by 2 dB, the compressor will act, so that the increase in the output is just 1 dB. With a Ratio set at 3:1, the increase in output will be 1 dB for every 3 dB above the Threshold and so on and so forth.

Next, imagine that the compressor has a reflex reaction to audio input. It can react to turning your input level down in milliseconds - specified by the Attack time. Just how long it takes to get back to it’s original position once it’s been moved is specified by the Release time.

When practised correctly, the result is that our tracks should sound more even and stable, reducing instances where our audio is too loud compared to quieter parts.

Got it? Good. Time to graduate.

What Is Multiband Compression

With all the previous parameters from traditional compressors crossing over to multiband compression, what then is the difference? Well, standard compressors affect the entire frequency spectrum of a signal, whereas multiband compressors affect only particular frequency areas - or bands - of the audio signal.

This is possible due to the nature of multiband compressors. They are able to separate incoming audio signals into a number of crossover frequencies, hence dividing the signal into multiple frequency bands, allowing independent compression to each band.

Again, the idea here is consistency. We want the high’s, mid’s and low’s in our instrument (or our overall mix) balanced well.

Right, let’s apply this knowledge to some practical scenarios.

Multiband Compression on Vocals

By compressing specific frequency bands, you can help shape and better control a lead vocal, especially because they tend to go through different registers over the course of a song. Adding multiband on a vocal track is a great way to smoothen out the mid-range as well as adding presence so that a dynamic performance sounds more balanced out and natural.

Vocals with too much of a low mid presence:

On a crossover of around 100-600Hz, focus your Threshold around -20 dB with a Ratio to taste.

Attack & release times are super important, and they depend largely on the syncopation of the vocal track i.e. are they quick rhythmically, like in a case of some rapping styles? Is it a legato note, like in the case of a sultry pop ballad?

It’s important to find a good balance between these times in order not to sound like you’re losing any of the vocal performance.

Here is a typical example of what we just covered using Fab Filter Pro-MB.

FabFilter CompressorVocals that need De-Essing:

Multiband compression on a harsh sounding vocal is super useful. Sibilances are those pesky “ess” and “tee” sounds that really poke through vocals, sometimes causing distortion. It also works great with plosives - the “pee” and “bee” sounds - in a vocal (this usually happens when the singer has sung too close to the mic).

This time, focus your attention on the higher end of the frequency spectrum and isolate the really sibilant band in the vocal. A good place to start is at around 6 KHz.

The Threshold and Ratio settings usually do depend on just how much of the sibilances are poking through, let’s say though a starting point can be around -24 dB on a 6:1 or 8:1.

This time the attack & release should be quick as you can afford (before removing any transients) seeing as how the “ess” sound comes and goes pretty quickly.

Here is a typical example of what we just covered using Fab Filter Pro-MB.

FabFiler - EQMultiband Compression on Bass

Using multiband compression on a bass is great for getting articulation out of a live bass recording, tightening up all of the lowest frequencies in the spectrum and reducing excessive “boom” and “woofiness”. We can do this all without affecting the mid to high range frequencies, which often carry the attack of the sound.

In order to clean up sub tones, aim you crossover points from 10 Hz to around 60 Hz.

For tightening the lower frequencies up, aim your cross over from around 60/70 Hz to around 200 Hz.

Again, depending on the nature of the bass tone, adjust the parameters accordingly. If the bass tones are too audible for your liking, turn the Threshold down, so that you are compressing more of the signal, and balance it out with the Ratio. The attack and the release again are responsible for how the multiband acts, so take in to consideration how the bass is being played.

Here is a typical example of what we just covered using Fab Filter Pro-MB.

FabFilter - EQ

That takes care of a few examples of how to utilise multiband compression. In the next part, we will be exploring some of the ways to effectively use multiband compression on your Mix Buss (Stereo Output/Master Fader) and how to dynamically control your song during mastering. I’ll also give a humble opinion on what I believe are the must-have digital multiband compressors on the market.

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