We hope that this article will help you to understand how to use a multiband compressor for mastering.
Multiband compressors are dynamic range compressors with the ability to affect separate frequency bands. Usually, the spectrum is divided to four frequency bands, but there’re some multiband compressors with an even greater number of bands. It is a great tool for mastering and polishing up the mix, which you can use to tame the kick drum if it sticks out or to get a more consistent low-end overall. It also helps to reduce frequency build-up in a lower mid-range and to tame harsh electric guitar sound without affecting the rest of the mix.
How To Use a Multiband Compressor for Mastering: explained
Before we dive into multiband compression for mastering, we have to figure out a few things first. Considering that most of you probably know your way around a compressor, the next few paragraphs could be somewhat of a redundancy, so you might choose to skip it. That said, conventional compressors and multiband compressors work very similarly, but you may freshen up your memory of how compressors work.
How compressors work
A compressor is a device or a piece of software that reduces the dynamic range of any input signal, which means that they have the ability to increase the volume of the quietest parts and to decrease the loudest. Usually, compressors are used in order to achieve a more coherent and detailed sound. Using the proper settings, you can, for example, soften a harsh and choppy electric guitar or give more punch to a kick drum.
Audio compression is where beginner audio engineers struggle the most, and the reason for that is that compression is rather confusing for an untrained ear, even though the process itself is pretty straightforward. In other words, to understand compression better, you’ll need to be able to hear it, and the best way to do that is a lot of practice. Regardless of your level, we have a few useful tips regarding compressor settings.
Compressor settings
Most of the compressors you could encounter with very few exceptions have the same very basic set of controls. Setting the “ratio” allows you to adjust the subtlety or intensiveness of the compression. Lower ratios will give you a very subtle and gentle compression. Higher ratios, on the other hand, will give you a very aggressive and obvious compression.
“Threshold” serves to tell a compressor at which volume of the given input signal it should start to work. There’re no strict guidelines on how to set a threshold, but generally speaking, a higher threshold makes sense if you want to tame the peaks, and a lower threshold could be used to bring up the sustain.
“Knee” is used to establish a correlation between a compressed and uncompressed signal. A softer knee will make a transition very smooth and almost undetectable. A harder knee, in turn, makes it more obvious.
“Attack” and “release” are considered to be two of the most important compressor settings. These two controls are designed to help you to shape the sound and the dynamics of the input signal. Attack and release settings are completely situational and vary greatly depending on a desirable result and the type of sound you are compressing. As a general rule, slower attack and release times are meant to bring up the sustains, and the opposite settings are used to tame the peaks.
Difference between compressor and multiband compressor
If you got yourself acquainted with conventional compressors rather firmly, you should be able to find your way around multiband compressors with ease. The thing is, multiband compressors and conventional dynamic compressors are exactly the same apart from one very significant difference. Multiband compressors have the ability to affect separate frequency bands and apply different settings to each of them.
Usually, the frequency spectrum is divided into two and up to four different bands, those being lows, low-mids, high-mids, and highs. Some multiband compressors have fixed frequency bands, and others let you adjust the range.
Multiband compression for mastering
It’s needless to say that having the ability to compress separate frequency bands is very beneficial in every mixing situation. Especially when it comes to mastering since we are dealing with a very wide frequency range where a lot of things are going on. That being said, multiband compression for mastering is just one of the options and not a necessity. Usually, this type of compression is used for fine-tuning and polishing.
With multiband compression, you certainly can attempt to “save” a mix that has a lot of problems, but as a general rule, it would be more efficient to redo the mix itself rather than trying to save it with compression. For mastering, regardless of the intention, we will use mostly very subtle and gentle settings. Remember, if you feel the need to use multiband compression for mastering rather aggressively, it means that there’s a somewhat significant problem. And it’s better to take a step back and fix it in the mixing stage.
Lows
When it comes to low end, you have several options here. If you feel like your kick drum sticks out too much, you can set a very fast attack and somewhat faster release to tame it without affecting the transients of the rest of the mix.
On the other hand, if you want a more consistent and commercial low end, use a slower attack and a very slow release. In both cases, you should use very moderate ratios and if your multiband compressor has a “knee,” set it somewhere around 10 dB. To tame the kick drum, set your threshold as high as possible and, for consistency, lower it down. Since we are looking for a very subtle compression, aim for 2-4 dB of gain reduction.
Most multiband compressors have the option of soloing different frequency bands, which you can do if you have the trouble of hearing a compression. Temporarily setting the ratio to higher values works too.
Low-mids
Usually, there’s a significant frequency build-up in the lower mid-range. You can easily fix this with an EQ, but at the cost of making your mix sound thinner.
The other option would be to use a multiband compressor within that frequency range. Since the build-up is usually very inconsistent, you can set your compressor to tame the low-mids only when the build-up is very high and noticeable the most. Set your ratio somewhere around 2:1 and use the somewhat slow attack. Use a very slow release, but try to make it very consistent with the pulse of the music. There’s a particular, very clever trick on how to do it.
Since we know that one minute contains 60 thousand milliseconds, you should divide 60 thousand by the BPM of your project. This will give you the exact length of your quarter note in milliseconds. Dividing it further by two will give you a length of an eighth note, then you can set your release according to the musical flow of your track.
High-mids
Usually, most of the energy of the vocal performance lies in the higher mid-range. Although conceptually vocal sounds very different from a kick drum, you can apply the same methods to it. If you have a very punchy vocal with a lot of transients, bring it down with a very fast attack and release. If you feel that a vocal needs a bit of expansion, use a slower attack and even slower release.
Since vocal performances tend to be very consistent musically, you can apply the same mathematical trick. Figure out the quarter note lengths for a very lyrical signing or find the eighth notes for a rap vocal.
In a higher mid-range, you can also find electric guitars. If your guitars sound too harsh, tame its transients with fast attack and release settings. In both cases, you should definitely use the lowest ratios possible. And while setting a threshold, don’t forget about the desirable 2-4 dBs of gain reduction.
Highs
You can use your multiband compressor in a high-frequency range to tame hi-hats if you feel that they stick out rather aggressively. Generally speaking, De-essers could be considered to be a somewhat limited version of multiband compressors. This means that you could use your multiband compressor exactly the same way.
On the other hand, it could be used to tame an occasional cymbals splash if it feels too harsh. In this case, use a meter to figure out the volume of a cymbal hit and set your threshold accordingly. A very fast attack and a somewhat slower release should do the trick, but you can feel free to experiment further.
