Although this may seem a little obvious, it helps to know that when you’re trying to perform bus compression, you need to insert the compressor on either your master output or an instrument group or stem. Bus compression always affects more than one instrument simultaneously.
With that in mind, it’s a powerful form of processing and a versatile one.
For example, I may want to perform mix bus compression. This means that I’ll insert the compressor on my mix’s output and compress the entirety of the mix.
Or maybe I want to compress the entirety of my percussion - if so I’ll insert the compressor on the drum bus or drum group and compress the entirety of that instrument group.
How much compression you apply to your bus will heavily depend on the instrument group that you’re compressing, your intended effect, and more. Although it’s best not to compress a bus more than 3dB, this isn’t the case in all circumstances, especially when compressing particular instrument groups.
For example, background vocals can be heavily compressed without the listener being made offset by the lacking dynamics. Additionally, it’s usually helpful to have this instrument group be as dynamically consistent as possible - for this reason, more aggressive bus compression is usually applied to BGVs.
If you’re using bus compression on your full mix bus, I’d say no more than 1 to 2dB of compression should be introduced.
Bus compression can be combined with other effects to create a distinct and unique sound from your mix or instrument group. Emphasis, de-emphasis, or emphasis and then de-emphasis techniques can be applied to your bus compression to control how compression occurs and the compression’s timbre.
If I wanted my high-frequency range to be less affected by the compression, I could lower its amplitude with an EQ prior to but compression. This would be a de-emphasis technique.
If I wanted the compressor to add some of its tonality to the vocal range, I would boost around 2kHz. This is an emphasis technique.
If you want to balance these cuts or dips after the compression occurs insert an EQ with equal and opposite curves to your first EQs.
One great way to control how a bus compressor affects the frequency spectrum of the mix or instrument group is they utilize an internal-side chain. An internal side chain lets you determine which frequency ranges will and will not trigger compression, in turn greatly altering the compressor’s behavior.
One of the most common examples of this is cutting out the low end when using mix bus compression. This way the kick or bass won’t trigger the compression.
This greatly reduces pumping and ensures that less compression occurs. Although the full frequency range will still be compressed when the compressor is triggered, the kick and bass will sound noticeably more present.
One of the best ways to introduce bus compression to a mix or instrument group is with a multi-band compressor - this offers a lot more versatility to your compression. Additionally, if the multi-band compressor offers mid-side processing, you can affect your stereo image.
Using the FabFilter multi-band plugin on a mix bus, I can target the lows, mids, and highs. For the lows, I’ll make the band mid and find where the bass interferes with the kick to try and tame that.
For the mid-range, I could compress the side around the vocal’s range to make the mid vocal louder in comparison.
For the highs, I could tame the mix if it was shrill, but introducing a shelf with a longer release.
Bus compression can be substituted with bus saturation which plays a similar role, but with the added benefit of harmonic distortion and non-linear forms of compression. Bus compression will give you more control over your attenuation, but bus saturation can result in a fuller, more impressive sound.
Saturator plugins vary greatly in regards to their timbre, and their ability to retain the fidelity of a signal, so be very careful when choosing a saturator for this purpose.
Saturn 2 is a great option, as is Presswerk from u-he, but to be honest there are a lot of great options.
Just be sure to enable dynamics processing in your saturator if that is an option.
One great way to creatively use bus compression is to combine it with bus expansion, ideally using a multi-band expander - this way you can simultaneously dynamically attenuate and amplify various aspects of the frequency spectrum. Combining the 2 effects gives you much greater control of the signal.
Using the FabFilter MB again, we can see that we have the option to expand the signal. So this time around maybe I’ll expand the kick while pulling back on the bass, or boost the mid vocal will attenuating the same side range.
Just like before we can affect our stereo image, all while have more control than we would with typically bus compression.