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VCA bus compression: what it does and when to use it

A VCA bus compressor makes a drum bus or a whole mix move as one with a few dB of gain reduction. What it does, who it is for, and how to set one.

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By Nolvra

Glue is a few dB, not a sound

A bus compressor sits on a group of tracks, a drum bus or the whole mix, and works on all of them at once. Its job is small. It takes two or three dB off the loud moments, and because every track in the group is pushed down by the same amount at the same time, the parts start to move together. People call that glue. It is not a tone you add, it is the kit or the mix reacting as one instrument instead of eight separate ones.

Why a VCA design does this job

A VCA compressor uses a voltage controlled amplifier as its gain element. It follows the settings you give it closely and does not add much character of its own, so the attack and release you choose are the attack and release you get. That predictability is why VCA designs are a common choice on drum buses and mix buses: you can set it fast enough to catch a snare or slow enough to let every transient through, and it does exactly that.

The settings that make it a bus compressor are simple. A moderate ratio, often 4:1 or lower. A slow attack, so the front of each hit gets through before the gain comes down. An auto release that follows the material, so it lets go quickly after a short hit and more slowly after a long loud passage. And a threshold set so the gain reduction only moves on the loud parts. The opposite of that, fast attack and heavy reduction everywhere, is still a valid move, but it is a different job, and most of the time it is better done in parallel.

Setting one up on a bus

Start from a preset for the bus

CLINCH opens on DEFAULT: 4:1, a 30 ms attack and Auto release, about 1 to 2 dB on a full mix. The library has 48 presets in six groups, DRUM BUS, MIX BUS, VOCAL GROUP, PARALLEL, INSTRUMENT GROUP and CREATIVE, each tuned on a real drum, mix or vocal recording to a set amount of gain reduction. Pick the group that matches the bus and audition from there.

Bring the threshold down until it moves

Turn THRESHOLD down until GR on the screen reads 2 to 4 dB on the loud hits, and less in between. RATIO goes from 1.5:1 to 20:1 and then MAX. If you want more control, raise the ratio before you push the threshold further. MAKE UP brings the level back.

Set the timing by ear

ATTACK runs from 0.1 to 30 ms. The slow end lets kick and snare punch through, the fast end tames them. RELEASE runs from 0.1 to 1.2 seconds, and AUTO follows the material. Start on AUTO and move off it only when you hear the level swelling back in the wrong place.

Compare at the same loudness

Switch on AUTO GAIN before you judge. It matches the processed loudness to the input, so the compressed version cannot win just by being louder. COMP turns the compression off inside the plugin without changing latency, which makes it a fair before and after.

Seeing what triggers it

The question a bus compressor raises most often is not how much, but why. Why is the mix pumping on every kick? CLINCH answers on its screen. The last four seconds scroll past with the input level, the output level, the gain reduction line coming down from the top and a dashed line at the threshold. Underneath, LOW, MID and HIGH show how much of the triggering comes from each range. If LOW is doing most of it and the mix pumps, the bass and kick are driving the compressor.

The fix for that is the sidechain filter. S/C HPF removes low end from what the detector hears, not from your audio, so the kick stops pulling the whole mix down while the bass stays full. S/C LPF and a bell do the same for the top and for one band. Press LISTEN to hear exactly what the detector hears while you set them. With EXT S/C on and nothing routed to the sidechain input, the screen says NO SIDECHAIN INPUT instead of leaving you wondering why nothing moves.

Who reaches for a bus compressor

  • Beatmakers who want the drums to hit as one kit rather than a pile of separate samples: a 4:1 drum bus with a slow attack.
  • Producers mixing their own records who want the mix to settle before the limiter: 1 to 2 dB at 2:1 or 4:1 on the mix bus.
  • Anyone whose mix pumps on the kick: a sidechain high-pass, so the low end stops driving the gain.
  • Vocal stacks and doubles that need to sit as one part: a light ratio on the vocal group.
  • Parallel compression on drums: the MIX control blends a crushed signal under the dry one, the move described in grit under a clean signal.
  • Anyone comparing settings by ear: equal loudness first, as in understanding LUFS, then the decision. The drum bus and mix bus settings guide goes preset by preset.

A bus compressor that shows its work

CLINCH is a VCA bus compressor with seven ratios, Auto release, a mix control, a sidechain you can listen to, a screen that shows what triggers it, and 48 presets.

See CLINCH

FAQ

What does a bus compressor do?

It compresses a group of tracks together, a drum bus, a vocal group or the whole mix. Because every track is turned down by the same amount at the same time, the parts move together, which is what people mean by glue.

What is a VCA compressor?

A compressor whose gain element is a voltage controlled amplifier. It follows its attack and release settings closely and adds little colour, which makes it a common choice for drum buses and mix buses.

How much gain reduction should a bus compressor do?

On a mix bus, usually 1 to 3 dB on the loud parts. On a drum bus, 2 to 4 dB is a common start. CLINCH's first-open card says the same: turn THRESHOLD down until GR reads 2 to 4 dB on the loud hits.

Why does my mix pump when I compress the bus?

Usually the kick and bass are driving the compressor. A sidechain high-pass filter takes the low end out of what the detector hears, so the gain stops dropping on every kick while the bass in your audio is untouched.

Does CLINCH add latency?

At the default 2x QUALITY it reports 35 samples to the DAW, which compensates for it. 1x reports zero, 4x and 8x report 41 and 44 samples. Set QUALITY before you print, because changing it changes the latency.

Does CLINCH run on Mac and Windows?

Yes. VST3 and AU on macOS 11 or later, Apple Silicon, and VST3 on 64-bit Windows.

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