D.I.Y. Multiband Compression

Multiband compression can be a powerful tool in your toolbox when mastering or mixing a song. Regular compression does its job, but sometimes individual frequency ranges need to be attenuated; this is where multiband compression shines.

Be aware, not every track need multiband compression; depending on the tools available to you in your DAW, there is room to shoot yourself in the foot. Even then, applying this technique may make your mix too flat by encouraging over-compression. As usual, use your ears.

If you have a regular compressor and crossover equalizer available, then you can create your own multiband compressor. This is how I do my mulitband compression as it allows me to have more control over how I process individual frequency ranges. For the purpose of this guide, I will assume that your crossover equalizer can is capable of splitting an audio signal into four different frequency ranges.

D.I.Y. Multiband Compressor

To do this, you will need at least five named audio channels at the minimum: source, bass, low-mid, high-mid, and treble. I am assuming that the audio that you want to multiband compress is in your source channel. After your channels are set up, follow these steps.

Setup Your Crossover Equalizer

1. Send you source to each of the channels that are named after a frequency range.
2. Apply a crossover equalizer to each channel named after a frequency range.
3. Ensure that the four crossover equalizers are configured to the same frequency crossover points
4. For each frequency range channel, configure its dedicated crossover equalizer to only let its designated frequencies through. This may be done by muting all other frequencies that are not designated for the channel.

Setup Your Compressors

1. After the crossover equalizers, add a regular compressor to each frequency channel. Ensure that you use the same type of compressor for each frequency channel.
2. Ensure your have configured in such a way that the latency introduced by each compressor is equal; you do not want to introduce phasing issues into your master. One common offender is the lookahead setting; if you use this for one channel, you have to use it for every other channel’s compression settings.

Visual Guide

A flowchart about the audio flow from the source channel, frequency range channels, and the final channel. There are arrows representing crossover equalization from the source to each frequency range channel. There are arrows, representing processing of equal latency, from each frequency range channel to a processed channel.

Gotchas

With power comes responsibility, D.I.Y. multiband compression gives you much more power; because each frequency range is split into their own channels, you can add processing to each channel besides compression. However, if you add an effect or processor to one channel, you have to apply the same processor to the other frequency channels to avoid phasing issues. Crossover equalizers are not perfect: there will be some overlap in frequencies when comparing, for example, the bass and low-mid channels after crossover equalization.

Final Thoughts

You can apply this construction when you do not have a multiband compressor or if you want to also add processing to individual frequency ranges. Having a dedicated multiband compressor will get the job done and prevent phasing mistakes, but I assume that you want the power of doing it yourself. This is the only way I can do multiband compression in my DAW and I am glad to be able to share this technique and what powers it enables, especially in mastering.