Top 11 Best Tips For Compressing The Mix Bus

Mix bus processing can be intimidating and can make or break a mix. Certain processes, such as compression, can help tremendously in polishing and finalizing a mix. There are no simple step-by-step instructions when compressing the mix bus because every mix is unique. However, there are certain considerations we should take into account if we choose to compress the mix bus, which is what this article is all about.

Before we go any further, I should state that there are no hard rules with compression or any other mixing process. The tips mentioned in this article are only suggestions and techniques worth considering when compressing the mix bus. No procedures work 100% of the time, and every mix is unique in its own needs.

Let's discuss each of these tips in more detail to give you important considerations when compressing the mix bus.

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Consider The Genre

The first tip I have for you is to consider the genre or style of music you're mixing. This tip spans far beyond mix bus compression and can be asked in regard to many other mixing processes, but we'll focus our discussion on mix bus compression here.

There are certain mix aesthetics that listeners have come to expect from certain genres of music. For example, an EDM hit will be mixed differently from a Country song, which will be mixed differently from a Metal song, and so forth.

Some genres are, generally speaking, more compressed than others. Think of Pop music, for example, and how much more compressed it is than Classical recordings.

So, keeping these “standards” in mind, we can err on the side of more or less compression or even no compression at all. This applies to the individual tracks, the buses, and, of course, the mix bus.

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Mix Into A Mix Bus Compressor

Mixing into a mix bus compressor is an effective way of mixing and plays right into the concept of top-down mixing.

Top-down mixing is a style of mixing that helps us focus on the holistic sound of the song and mix. We begin by focusing our efforts on mix bus processing (including compression) before moving on to the subgroups or instrument buses and finally reaching the individual tracks if they require any additional processing.

As mentioned, top-down mixing keeps the entire mix at the forefront of our attention, which can keep us from getting lost in the minutiae of processing individual tracks.

Additionally, we can often achieve more natural results with fewer processors using this approach, as many common issues found in individual tracks can be solved at the bus level.

Here's an over-simplified graphic to show the basics of top-down mixing with the mix bus at the top and the individual tracks at the bottom:

Once we have completed proper gain staging and have gone through our initial mix with faders, pan pots and any necessary high-pass filtering (to eliminate excessive low-end rumble), it can be a good time to insert a compressor on the mix bus and mix into it.

Set the compressor to subtly clamp down on the entire mix to taste, helping to glue the mix together and enhance any stereo panning you have going on.

So long as we maintain proper gain staging (not having any plugins alter the volume of any tracks too much), we should be able to mix into the compressor without tweaking it throughout the mix.

Of course, as we add parallel processing and time-based effects returns, we'll undoubtedly increase the level of the mix, so we should check out mix bus compression periodically to ensure we aren't over-compressing. However, we'll often make the adjustments naturally throughout the mixing process to drive the mix bus compressor appropriately.

Contrast this against inserting a compressor after we've completed the mix. In this case, any compression will alter the mix we've worked so hard to create, and sometimes for the worse.

When it comes to mix bus compression, it's often best to insert the compressor as soon as possible and mix into it rather than mess with the overall mix closer to the end by inserting it later.

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Keep It Light

Mix bus processing is often daunting, and it should be. We are affecting the entire mix, after all.

We can often get away with pretty aggressive compression on individual tracks, especially when mixing in genres where higher levels of compression are commonplace (see Tip 1: Consider The Genre).

Vocals, for example, often benefit from significant amounts of compression to sit right up front in the mix.

However, dynamics are crucial in music. Without dynamics, music would be flat and boring. So when it comes to mix bus compression, which acts on the entirety of the mix, it's generally best to only compress a little bit, if at all.

1 or 2 dB of gain reduction at the peaks, with a low ratio of 1.5:1 or 2:1, is often enough to help glue the mix together into a more cohesive-sounding record. I'd recommend starting there.

Be cautious about compressing any more (it can sometimes sound great), and be sure to A/B test when necessary to gather a more objective opinion as to whether the compressor is helping the mix or not.

When A/B testing, ensure the makeup gain is set so the mix bus is at the same level and loudness regardless of the compressor settings or if the compressor is on or off. Switch between the different settings or turn the compressor on and off and listen critically to which serves the mix best. Make adjustments to the compressor parameters as necessary to get the best results.

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Dial In The Time Variables

Compressors don't act instantaneously to reduce audio levels. Rather, they have attack and release times that affect how they interact with the audio they're compressing.

The attack time is the amount of time it takes for a compressor to engage/react once the input signal amplitude surpasses the threshold. It's a rate of change whereby the compressor gradually reaches its full ratio over time. It's not a delay of action, where the compressor will clamp down fully after a set period of time.

The release time is the amount of time it takes for the compressor to disengage (to stop attenuating the signal) once the input signal drops below the threshold. Like the attack time, it's a rate of change whereby the compressor gradually disengages over time. It's not a delay of action, where the compressor will suddenly stop compressing after a set period of time.

Dialling in these attack and release times will allow the compressor to work more musically with the mix. We can time them well to the rhythm of the song to enhance the movement, set the attack to control the transient perfectly, and tweak the release time to avoid pumping and add musical movement to the song.

I recommend starting with a slower attack time and a longer release time and working from there.

Dial the release time so the mix bus compressor works with the song's rhythm. Adjust the attack time to taste (on the mix bus, fast attack times are often best for glueing the mix together instead of shaping the transients, which may cause pumping).

Shorten the attack time until you begin losing the impact and definition of the transients. Once you hit that point, consider if the mix needs to be a bit smoother or more aggressive. If it needs smoothing, consider shortening the attack time further. If it needs more aggression, consider lengthening the attack time.

Increase the release time to fit with the rhythm/tempo of the song. Set the release time so that the compressor has just enough time to disengage before it's triggered once again by the following transient. Once you hit that point, consider if the mix needs to be a bit smoother or more aggressive. If it needs smoothing, consider lengthening the release time further. If it needs more aggression, consider shortening the release time.

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Compression For Colouration

Many compressors will add their own “character” to the audio they're processing. This is especially true of hardware compressors and those plugins that emulate them.

This inherent colouration of audio can help enhance certain elements of the mix, causing subtle but pleasing amounts of saturation and distortion, even if the compressor isn't applying any gain reduction.

A bit of colouration across the entire mix can be helpful to bring out some liveliness and bring elements closer together in a more cohesive-sounding mix. The “imperfections” of colouration are especially useful in digital systems, including digital audio workstations, where the audio is often sterile and even too “perfect”.

However, going too far or opting for the wrong compressor can worsen the mix. We must listen critically and even utilize A/B testing to ensure our mix bus compression is actually helping.

So colouration can be a good or bad thing. Regardless, we should keep the inherent sonic characteristics of our compressors in mind when applying mix bus compression.

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Consider The Song's Long-term Dynamic Structure

I touched on the importance of dynamics in music in Tip 3: Keep It Light. Beyond the dynamics with a short-term timeframe (drum transients, vocal lines, etc.), we also have the long-term dynamics of the song.

A great song will tell a story with points of high energy and low energy. These energetic dynamics throughout the song manifest in different levels within different sections. For example, we can expect the climax to be louder than a break.

We ought to be aware of the long-term dynamics of the mix and utilize any mix bus compression accordingly.

For instance, setting the compressor to apply subtle gain reduction at a low-energy section could potentially lead to severe over-compression at the climax.

Rather, it's often best to begin mixing at the section with the highest energy. This is especially true of mix bus compression.

It's often okay if the quieter parts aren't triggering the compressor. It may even be beneficial to only have the mix bus compressor kick in in higher-energy sections to help glue the elements together within these louder sections.

At the same time, we should investigate how any gain reduction in the louder parts closes the loudness gap between the loud and quiet sections. Too much compression can flatten out the long-term dynamics, causing the arrangement of the song to lose its impact as it grows in energy.

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Use Your Ears

This one may be a bit obvious, but it's essential that we use our ears when inserting mix bus compression and mixing into it.

Any tips I could give you in this article are null and void if they don't serve your tastes or the mix as a whole. It's impossible to give instructions about specific parameter settings because every mix will demand something different.

While I can give you good starting points and general advice, the best piece of advice I could ever give you when mixing is to use your ears.

If the mix bus compression doesn't sound good or serve the mix, either get rid of it, change the compressor being used, or adjust the parameters of the current compressor. Rely on your ears (and A/B testing) to show you the way!

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Think Glue

Glue is the sense/perception that sounds belong together and exist within the same world in the mix.

This “glue compression” is one of several ways to make an entire mix sound more cohesive, which is the ultimate goal of mixing, to begin with.

This happens because the compressor can be triggered by a single element/track in the mix but affect all the other elements in the mix. This simple relationship ties the various mix elements/tracks together and leads to better cohesion in the mix.

I talk about the concept of glue in more detail in this video:

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Mix Bus Compression Is Not Mastering

Simply running our entire mix through a compressor is not really mastering. Although there may be a trend to master our music within our mix sessions, it's generally best to think of these music production processes as distinct from one another.

So, while mix bus compression can help glue things together and even enhance the potential for overall loudness, we shouldn't confuse it with mastering.

Don't worry about cranking the makeup gain so that we get maximum loudness from the compression.

Furthermore, don't feed the compressor with low-headroom audio. Gain staging still applies at the mix bus level, and it's usually best to drive our mix bus compressors with appropriate levels, several decibels below full scale, to ensure optimal performance. This is true of many hardware compressors and even plugins, especially those designed to emulate hardware.

Although compression is sometimes used in mastering (limiting is technically more popular for loudness maximization), we shouldn't confuse mix bus compression with mastering processing. Focus on the mix first, with the mix bus compression, before moving on to mastering.

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Know When To Revisit Individual Tracks In The Mix

We discussed a top-down approach to mixing in Tip 2: Mix Into A Mix Bus Compressor. However, compressing the mix at the mix bus isn't necessarily a fix-all for controlling the dynamic range of our music.

It's often the case that compression will be required on instrument and vocal buses and certain individual tracks. Compressing individual tracks makes us use more processors but ultimately gives us more control over the mix's dynamics and the interplay between the elements we're mixing together.

Of course, if we have a proper balance of elements in the mix, nothing should be poking out too far to cause the compressor to act more than it should. However, if an individual mix element isn't sitting right when compressing the mix bus, we should revisit it at the track level rather than relying on mix bus compression to do the job for us.

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Process The Sidechain

The final tip I have for you is to process the sidechain of the mix bus process if need be.

The most common process for mix bus compression sidechain signals is the high-pass filter, which can reduce or eliminate the effect the low-end frequencies have on the compressor.

So, if we're dealing with a bass-heavy mix that causes unwanted pumping in the mix bus compressor, we can opt to engage the high-pass filter on the sidechain signal path (if the option is available in our mix bus compressor).

That way, only the frequencies above the HPF will act to cause any gain reduction in the mix bus compressor, making for a more natural-sounding compression with less pumping.

Of course, this strategy is likely unnecessary if the low-end frequencies aren't overly represented in the mix. However, it's worth mentioning here for those of us involved in mixing bass-heavy music, particularly in songs with strong kick drums and other transients in the low end.