1
Sidechain Compression: Beyond EDM Pumping
A normal compressor reduces gain based on its own input. A sidechain compressor reduces gain based on an external "key" signal you route into its sidechain input. So the bass can be ducked by the kick (not by itself), a synth pad can be ducked by the lead vocal, or a rhythm guitar can be ducked by the vocal, all without manual automation.
The sound people associate with sidechaining is the obvious EDM "pump", a heavy kick visibly ducking a synth bass every beat. That is one use. The far more common use across rock, country, pop, and acoustic mixes is subtle, inaudible-as-an-effect ducking: 1-3 dB of gain reduction on the bass when the kick hits, or on the rhythm guitars when the vocal enters, that clears space without the listener ever hearing the compressor work.
In practice: Country kick and bass masking each other in the 80-120 Hz range: route the kick to the bass compressor's sidechain, set 2-3:1 ratio with 1-3 dB of gain reduction. The bass ducks subtly on each kick hit, no pumping, just a tighter low end.
Sidechain = compressor triggered by an external key, for ducking frequency masks, not just for EDM pump.
2
Mix Bus Attack Time: Preserving Transients
A slow attack (10-30 ms) on the bus compressor is critical for acoustic music. It lets the initial transients, pick attacks, bow strokes, plucks, vocal consonants: pass through before the compressor engages, preserving the articulation and life of the instruments.
A fast attack catches and reduces those transients, flattening the mix. In bluegrass, the transients are the music.
In practice: A/B-ing 3 ms vs 30 ms attack: the 3 ms sounds "smoother" only because it is eating every pick and chop transient, choose 30 ms so the drive survives.
Slow bus-compressor attack (10-30 ms) lets transients through, fast attack flattens acoustic music.
3
When NOT to Bus Compress
Bus compression is not always appropriate. Very dynamic acoustic performances, solo classical guitar, an intimate vocal-guitar duet, classical recordings: often sound best with none. The natural dynamics are the artistic intent.
Solo performances also lack the frequency density a bus compressor responds to well, so it may pump awkwardly on single-instrument transients. Sometimes the right move is no compressor.
In practice: A solo classical guitar recording: skip bus compression entirely, the dynamic swing from pianissimo to fortissimo is the performance.
Skip bus compression on very dynamic solo/intimate acoustic recordings, the dynamics are the point.
4
Bass-to-Kick Relationship Across Systems
In acoustic and bluegrass mixing, the upright bass and a kick or stomp box both occupy the sub-100 Hz range, exactly where playback systems vary most. On full-range monitors they coexist; on bass-boosted car stereos they pile into mud; on phones and laptops both vanish.
The fix is frequency separation: give the bass its fundamental space (60-100 Hz) and the kick its attack space (100-200 Hz thump), with each relying on upper harmonics to translate to small speakers.
In practice: An upright bass and stomp box tight on monitors but a boomy mess in the car and inaudible on a phone: HPF the stomp box at 60 Hz, separate their ranges, add bass harmonics at 200-400 Hz.
Bass and kick both crowd sub-100 Hz, separate their ranges and lean on harmonics for small speakers.
5
Low-End Management for Small Speakers
Small speakers cannot reproduce frequencies below 100-150 Hz, but the brain still perceives bass, through the "missing fundamental" effect: it infers the low note from the harmonic series above it.
So a bass that translates needs rich harmonic content in the 200-800 Hz range. A gentle boost around 400-600 Hz brings out that midrange presence, making the bass audible on every system, not just full-range monitors.
In practice: An upright bass that vanishes on laptop speakers: add saturation for harmonics and boost 400-700 Hz, small speakers reproduce that, and the brain infers the fundamental.
Small speakers can't reproduce sub-150 Hz, bass translates through its 200-800 Hz harmonics.
6
Parallel Compression (NY Compression)
Parallel compression, "New York" compression: blends a heavily compressed copy of a signal underneath the original dry signal. The dry signal keeps every natural transient and full dynamics; the crushed signal adds sustain, body, and density underneath.
The result is punch and consistency without the squashed sound: you raise the quiet parts without flattening the peaks.
In practice: An upright bass with great dynamics that vanishes in loud ensemble sections: blend a hard-compressed parallel copy underneath, the dry woody attack stays, the parallel fills the gaps.
Parallel compression blends a crushed copy under the dry signal, punch and sustain without squashing.
7
Gain Staging the Mix Bus
Analog-modelled bus plugins are calibrated so that -18 dBFS corresponds to 0 VU on the hardware they model. That is an AVERAGE level, measured on a steady tone, not a peak level.
So aim for an average of about -18 dBFS on the mix bus. Music with a normal crest factor runs 12 to 18 dB above its average, so that leaves peaks somewhere around -10 to -6 dBFS with plenty of headroom left.
Both errors are common. Too hot and the compressor and saturator overreact and sound harsh. Too quiet, which is what happens if you set the PEAKS to -18, and they barely engage: the average lands near -32 dBFS and the plugins do almost nothing while you turn their knobs up wondering why.
In practice: An SSL bus comp and tape plugin sounding harsh at gentle settings: the bus averages around -9 dBFS. Pull the faders down collectively until the average reads -18 and the peaks land near -8, and they smooth out.
The -18 dBFS calibration is an AVERAGE, not a peak. Average about -18 dBFS, peaks near -10 to -6.
These lessons are the teach side of knowledge cards from the Studio Mix deck. In the daily plan each one is followed by a quiz, spaced over weeks, so it stays known rather than read once.