Bus compression, and where “glue” comes from

The fast VCA that makes a mix sound like one performance rather than a stack of tracks — ratio, attack, release, and the sidechain filter that keeps the bass out of it.

In the Sonic Station finisher: VELVET BUS — VCA bus compressor

The fast one, and the source of the word 'glue'. A quick VCA with a stepped ratio and a sidechain filter that keeps the bottom octave from ducking the whole record. Where LUMA smooths, this one moves with the drums and makes a mix sound like one performance rather than a stack of tracks.

The controls

Every range and starting value below is the one the processor actually uses — this page is generated from it.

Threshold

-50.0 dB to 0.0 dB · starts at -18.0 dB

How far down it starts working. Bring it down until the meter twitches on the loud parts, then stop.

Ratio

1.5:1 · 2:1 · 4:1 · 10:1 · starts at 2:1

2:1 is the classic mix-bus setting. 4:1 for something that needs holding down; 10:1 is a limiter and rarely what a whole mix wants.

Attack

0.1 ms · 0.3 ms · 1 ms · 3 ms · 10 ms · 30 ms · starts at 10 ms

Slower is punchier: at 10 or 30 ms the drum hits get through before the gain moves, which is what makes a mix feel like it's pushing.

Release

100 ms · 250 ms · 400 ms · 800 ms · 1200 ms · starts at 250 ms

Set it so the gain comes back in time with the song. Too fast and it pumps; too slow and it never lets go. Auto is a reliable place to start.

Makeup

0.0 dB to +20.0 dB · starts at 0.0 dB

Put back what the compressor took. Level-match before you decide it sounds better.

Blend

0% to 100% · starts at 100%

Blend the uncompressed mix back in. 70–80% is glue with the punch left in.

SC filter

Off · 40 Hz · 60 Hz · 90 Hz · 120 Hz · 200 Hz · 300 Hz · starts at 60 Hz

Keeps bass out of the detector. Without it a loud kick pulls the whole mix down on every beat — this is the single most useful control on a bus compressor.

Release mode

Manual · Auto

Auto runs a fast and a slow release at once and follows whichever suits the moment. Hard to make sound wrong.

Sonic Station's mix finisher runs this entirely in your browser — the audio is never uploaded anywhere.

Read next

• Optical compression: the slow one

  What a photocell does to timing, why an opto can hold a whole mix steady without anyone hearing it, and when to reach for one instead of a faster compressor.

• Tape saturation, and what people mean by “warm”

  Half-inch at 15 ips: a head bump in the low end, a soft top, and transients rounded off a hair before the limiter has to work for a living.

• Loudness targets for Spotify, Apple Music and YouTube

  What LUFS to master to, what every streaming service does to a record that arrives louder, and the true-peak ceiling to leave under it.