Sidechain compression makes one track duck out of the way of another. The compressor sits on the track you want to move — usually the bass — but listens to a different track, usually the kick. The result: the low end has room for the kick on every hit, without you turning the bass down overall.
There are really two uses, and they need different settings. The utility version is inaudible and solves a frequency-collision problem. The pumping version is an audible rhythmic effect.
A normal compressor reduces gain when the signal it is processing gets loud. A sidechained compressor reduces gain when a different signal gets loud. That other signal is the key input or trigger.
The kick and the bass both live below roughly 150 Hz. When they play at the same time, they sum, the meter jumps, and the low end sounds bloated and unclear. Ducking the bass by a few dB for the duration of the kick transient removes the collision entirely.
The goal is that you cannot hear the compressor working, only the clarity it produces.
| Control | Starting point | Why |
|---|
| Ratio | 4:1 | Enough to move the bass without squashing it |
| Attack | 1–5 ms | Fast, so the duck happens with the kick, not after it |
| Release | 60–150 ms | Must fully recover before the next kick |
| Gain reduction | 3–6 dB | Felt, not heard |
| Knee | Soft | Smoother onset |
The release time is the setting people get wrong. At 128 BPM a sixteenth note is about 117 ms, so a 250 ms release means the bass never returns to full level between hits and the whole low end sounds limp. Time the release to the gap, not to a habit.
If your compressor has no external sidechain input, duplicate the kick to a muted send, or use a dedicated sidechain plugin driven by a MIDI trigger.
House, progressive and big-room EDM use sidechaining as a rhythmic device on pads, chords and sometimes the whole mix. Here the settings invert:
- Gain reduction: 8–15 dB — obvious and deliberate.
- Release: 200–400 ms, or roughly the length of a quarter note at your tempo, so the sound swells back in just as the next kick lands.
- Trigger: often a silent four-on-the-floor MIDI kick rather than the real kick, so the pump stays constant even when the kick pattern changes.
The tell of a well-programmed pump is that the shape of the recovery is musical. A volume-shaper plugin drawing an exact curve is usually more controllable here than a compressor, because you set the envelope directly rather than inferring it from threshold and release.
Volume automation. Drawing 3 dB dips by hand is more work, but it is exact, it never mis-triggers, and it does not change the tone of the bass. Best for sparse arrangements and for acoustic material where a compressor artefact would be obvious.
Dynamic EQ or multiband. Instead of ducking the whole bass, duck only 40–100 Hz. The mid-range growl of the bass stays constant, which keeps the part audible on small speakers while still clearing the sub for the kick. This is often the better answer in hip-hop and pop.
Fix it with EQ first. If the kick peaks at 60 Hz and the bass at 90 Hz, a narrow cut in the bass at 60 Hz and a cut in the kick at 90 Hz may solve the problem with no dynamics processing at all. Try this before reaching for a compressor — static separation beats dynamic separation when it works.
Solo the kick and bass together, then loop four bars. If the kick loses weight when the bass enters, the duck is too shallow. If the bass sounds like it is gasping, the release is too long. Then listen in mono on a small speaker — that is where low-end collisions are most obvious.
Related reading: mixing bass, mixing drums, and EQ and compression basics.
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