How to use compression on the master bus

What master compression is for

A compressor on the master bus hears the whole mix at once. When the kick and snare hit, it turns everything down a little, and when they stop, it lets everything come back up. That small, shared movement makes the parts sound like they were played together in one room. People call it glue.

That is the only job it has. It does not fix a vocal that jumps out, a bass that booms on one note or a snare that is too loud. Those are mix problems, and they need moves on their own tracks. A master compressor trying to hold back one loud part turns the whole mix down every time that part plays, and everything else pumps with it.

So keep it gentle. The main stage on this page uses the RMS detector at 1.5:1 to 2:1, an attack of 10 to 30 ms and auto release, and it takes only 1 to 2 dB of gain reduction. The slow attack lets the front of each drum hit through, so the mix keeps its punch. Auto release follows the music, letting go quickly after short hits and slowly after long, loud passages. The Compressor in the free kit's Club Test Master rack starts the same way, on RMS at 2:1 with a 30 ms attack and auto release.

Some styles want more. A dense club track or a loud rock mix can sound loose with only 1 dB, and the optional second stage pushes to 2:1 to 3:1 and 2 to 3 dB. Use it when the squeeze is part of the sound you are after, not as a way to make the mix louder.

Many people mix into the master compressor from the start, so they hear the glue while they balance. That works well, as long as it stays gentle. If you add it at the very end instead, check the balance again afterward, because even 1 or 2 dB can shift how the parts sit.

Compression is not loudness

A master compressor at these settings barely changes how loud the mix is. That is on purpose.

Loudness comes from the limiter, the last device on the master. A limiter stops the peaks from going past a ceiling you set, so you can turn the whole mix up without clipping. In Live, that is Limiter, and it comes with every edition. The compressor goes before it and shapes how the mix moves. The limiter after it sets the final level.

If you push a compressor to make a mix loud, it has to take a lot of gain reduction, and the mix starts to pump and lose its punch. The drums go soft, the low end swells between hits, and the track sounds smaller even as it gets louder. Let each device do its own job.

This is also why Makeup stays off in the settings on this page. With Makeup on, the compressor turns the mix back up after it turns it down, and a louder mix always sounds better at first. That makes it hard to hear what the compressor is really doing. Match the level by ear instead.

Compare against a reference at the same level

Your ears can't judge master compression well on their own. The changes are small, and you have heard the mix so many times that you stop hearing it clearly. A reference track helps.

Pick a finished song in the same style that you like the sound of. Put it on its own track and set that track's output to Ext. Out and pick the same outputs as your Master, usually 1/2, so it skips the master compressor and limiter. Then turn it down until it plays at the same loudness as your mix. That last part matters most. A finished master is much louder than a mix in progress, and if you compare them at different levels, the louder one always wins.

Now switch between them. Listen to how the drums hit, how steady the vocal sits and how the low end moves. If your mix sounds loose next to the reference, a little more glue may help. If yours sounds flatter, you are taking too much.

Do the same with the compressor itself. Switch it off and on with the level matched, and keep it only if the mix sounds more together, not just louder.

Mistakes on the master bus

Too much gain reduction is the main one. When the meter moves more than about 2 dB, the whole mix starts to breathe in and out with the kick. Raise the threshold until it only moves on the loudest hits.

A fast attack is the next. It grabs the front of every drum hit and the mix goes soft and far away. Keep it at 10 ms or slower.

Using the master to fix the mix is another. If one part is the problem, fix that part.

Stacking compressors on the master is the last. One gentle compressor and a limiter are enough for most mixes.