What is a Multiband Compressor? – and how to use it!

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We take a look into Compression and discuss the ins and outs of Multiband Compression so you know how to use it in your productions.

Compression is one of the most commonly used techniques in music production with producers using them to manipulate sounds into the music we hear today. There is a lot to know about compression even though the main concept of compression is relatively simple. Today we look into the world of compressors with a focus on Multiband Compression covering what it is and how it works along with some examples of how it can be applied to your productions.

It is suggested that Multiband compression was borne from the old days of radio. Apparently, they needed to add compression to the low end of the audio signal so that it did not interfere with the radio frequency, and so warping the entire signal. These Multiband Compressors were likely a combination of multiple hardware EQ and Compressor units routed together. However, this is all hard to confirm and so we just accept that we have this technology today!

Terminology

I remember being confused with the difference between Multiband Dynamics, and Multiband Compression, but don’t worry! These terms are almost always interchangeable with Multiband Compression being the term of choice for most people these days.

 

What is a “Compressor” and how does it work?


Those of you who are new to compressors and compressor plugins may be wondering, well what is a compressor? I remember the first time I came across the term and all I could think of was the compressor in the fridge that helps keep the food cool somehow. Obviously that is not what we are talking about here, so let’s bring it back to a music production context.

What it is

A compressor plugin is used to decrease the dynamic range difference between low volume and high volume sections in an audio signal. This means that a compressor is able to squash/reduce the peaks in volume while bringing up the quiet parts of an audio signal. An example of an uncompressed audio signal is…

…say you are watching a movie and you find yourself having to turn up the volume when the actors are talking, and then turn it down again when there is a car chase. You could use a compressor in this case to bring the talking volume and the car chase volume closer together making for a much less annoying experience.


How it works

A compressor has a few key parameters:

  • Threshold – approximate volume level you don’t want to go over
  • Ratio – how much volume reduction to apply
  • Attack – how fast you want the reduction to be applied
  • Release – how fast you want the reduction to be removed
  • Gain Boost – additional volume increase after compression is applied

A compressor works by `listening` to the incoming audio signal and waits for the signals’ volume to reach the Threshold. When it does it will wait for the duration of the Attack, after which it will start to apply volume reduction at the Ratio specified. Once the signal has fallen back below the Threshold again the compressor will wait for the duration of the Release, and then stop applying volume reduction. The Gain Boost is applied the hole time since it is applied after the compressor (in most compressor plugins) has done its work. The point of this is that since we are effectively lowering the volume level of the loud parts, the over all volume may become too `quite` and so we bring up the quiet talking with the Gain Boost.

It is important to remember that the compressor only does `work` when the input signal is over the Threshold level. The amount of work it does is defined by the Ratio where if a ratio of 3:1 is used. Then for every 1 db the input signal is over the Threshold level, 3 db of gain reduction will be applied.

Here is an example of a drum loop audio signal wave form in its original state, and then after it has had a compressor applied. You can see that the audio signal has become less `spiky` in that, the loud parts and the quiet parts are now closer together and, over all the signal appears thicker/louder.

 

Compressor vs. Multiband Compressor


Now we know what a compressor is and how it works Let’s contrast and compare it to a Multiband Compressor.

Let’s get what they have in common out of the way because its kinda obvious. They are both compressors that work just like we have discussed above. They take the `loud` parts of an audio signal and bring them closer to the `quiet` parts of the audio signal.

OK great… Now the differences.

A Multiband Compressor is essentially two or more compressors joined together that are each given a Frequency Band to focus their work on.

What is a Frequency Band

The human ear is able to hear frequencies somewhere between 20 Hz and 20 kHz and so a frequency band can be thought of as any group of consecutive audible frequencies. For example below we have an EQ allowing a band of frequencies through between approximately 100 Hz and 1 kHz.

What a Multiband Compressor does is split the work of a single compressor working on all frequencies at once, to many compressors focusing on a specific band of frequencies. This allows for far more control over the audio signal and flexibility when applying compression.

So just like a regular compressor there are all the same parameters like Threshold, Ratio etc but this time the Compressor is not only watching for the audio signal to go over the Threshold, level but it also must be specific frequencies that do so. This way you are able to apply different amounts of compression to different areas of the frequency spectrum. Take a drum kit for example, it has the low kick drum, mid snare and toms, and the high hi-hats. In this case you may want to apply a different amount of compression to the Kick drum than you do to the hi-hats and this is where a Multiband Compressor can help!

 

Example uses


Here we have put together a few great examples of how to use a Multiband Compressor to give you and idea of what is possible.

Vocals

The first video we get to see Toni Maserati using a Multiband Compressor on vocals


Guitar

This video we have Andy Sneap showing us how to apply Multiband Compression on a Rock guitar riff.

 

Mastering


Below are a few ideas and things to keep in mind when mastering with compression and mastering in general. They are not specific to any plugin, rather it is more of a general discussion on the topic.

Try a Multiband Compressor

Next time you are mastering a record why not try a Multiband Compressor in place of a normal Compressor. This will give you greater control over your mix allowing you to be more precise with your compression. It is great if all you want to do is tame a heavy bass line for example.


Listen

Especially when adjusting the attack and release parameters, rather than focus on a particular number like 35 milliseconds of attack and 350 milliseconds of reals. Focus on listening, for example if you are applying compression to a kick drum, adjust the attack so that you do not hear any distortion or artifacts caused by the compressor.


Band Solo

Feature is to have a solo function on the Band you are working with. This allows you to not only choose the right frequency band to work with but also compare different band to see how they work together. A good example of this is the Waves C4 Multiband Compressor that we saw Toni Maserati use in a video above.


Beware of EQ-ing

This is a very important thing to remember when applying a Multiband Compressor to a master bus. Since you are applying different amounts of gain reduction to the audio signal at different points along the frequency spectrum, you are essentially EQ-ing the signal. This most often happens when you apply too much compression in different areas.

The way I think about it in this case is, and EQ makes frequencies louder or quieter, and a Multiband Compressor makes frequencies sound tighter or punchier. If you try to keep this in mind when using these tools you will be much better off and hopefully avoid over processing the audio signal.


Make a Copy

This is a handy tip, if you have a final mix down of a record ready for mastering, make two copies of it. The first copy you can call `Original` and the second you can call the `Mastered`. Now you have the original track to switch back to as you work on the mix. This allows you to identify quickly if, what you are doing to the record, is what you and/or your client wants. It helps with keeping objectivity when listening as mastering a record.


Take Regular Breaks

The final point I would like to mention here is take regular breaks when mastering. After too long at the mixing desk your ears will lose objectivity and get too comfortable with how the mix sounds. I will usually spend around 45 minutes on a single record before taking a break from it. Things that help me reset are;

  • getting up and walking out of the room, even if I just walk down the hallway and back;
  • listen to a reference track – I have a few records that I keep on my phone and computer that I use to completely take my ears away from what they are working on.
  • Talk to someone – I find my ears have to `wake up` and switch from listening to music to listening to someone talk

Regarding reference tracks, one of my favorite reference tracks to listen to is linked below. Written by Hans Zimmer, this record is so different to what I am working on most of the time that again my ears have to `wake up` and listen to something different.

This record may not work for everyone but, everyone will have something that makes their ears `wake up` and have to work again.

 

Conclusion


Multiband Compression is a great technique to master since it gives you greater control over the frequency spectrum than a `regular` compressor does. You are able do things you otherwise wouldn’t be able to do (easily) such as to tighten up heavy and lose sound bass frequencies without touching the other frequencies in a mix.

I hope this article has been helpful in your understanding of what Multiband Compression is and how to use it. If you have any questions or experience with Multiband Compression then I encourage you to share your thoughts with us in the comments section below.

As always if you liked this content then hit the like button below and if you didn’t then leave us a comment telling us what we can do better!

Thanks for reading!

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6 thoughts on “What is a Multiband Compressor? – and how to use it!”

  1. This isn’t a topic I am familiar with, however as a newbie I found your article quite easy to follow and everything was explained really well and I came away having a good understanding of what a multiband compressor was. I also like how you kept referring back to when you were a ‘newbie’ and what your first impressions were, so it made it very relatable to people with little to no knowledge.

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  2. Hi Tim,

    I rarely post comments on the internet, but I couldn’t go without thanking you for this amazing article which contains a lot of helpful information. As a newbie in this field, I struggle with understanding how all that works and how to use it..  However, I must say that I learned quite a lot after reading your article and I find it to be really easy to understand. I would definitely recommend it to people having difficulties understanding the Multiband Compressor.

    Many thanks,Nick.

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  3. I have very little experience in this field and when I look at boards loaded with buttons and knobs and switches, I’m lost. Not so with this post, nicely done and very educational. Gives us a good idea of what goes on behind the scenes in music production and movie production. Not just a matter of recording and selling.
    Some of the tips are even useful for those of us who produce educational videos for post online. Sometimes you hear the music and barely make out the wording. You can certainly identify those who have experience in this field and those who don’t.

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    1. Thanks Mitchguy, glad it was helpful.
      You are quite right, there is a lot of work that goes into an album for example, or an content creation for that matter.

      Cheers

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