DJ Toolkit
Mastering Dynamics

Compressor Threshold Helper

Most beginners turn a knob until "5 dB of GR" sounds right, without ever seeing what that means on the input / output relationship or in time on a real transient. Set your compressor's threshold, ratio, knee, attack, release and makeup — the transfer curve redraws immediately, and a synthetic kick + snare fires through the same maths so you can see the gain reduction envelope over time.

Compressor settings

Transfer curve (input → output)

Dashed diagonal is bypass (1:1 ratio). Solid line is the actual output. The shaded knee region is where compression begins gradually.

GR over time on a kick & snare

Max GR: 0.0 dB

Inputs labelled "kick" are −6 dBFS at t=0 with 60 ms decay. "snare" at 500 ms with 120 ms decay. Adjust attack/release to see how the envelope changes.

Working GR at -6.0 dBFS input

GR
2.0 dB
Output (post-makeup)
-5.0 dBFS
Threshold & ratio
-18 / 3:1
Headroom to ceiling
5.0 dB

How to use

  1. Pick a preset (Vocals / Drums / Bass / Master) to load sane starting values — then tweak by ear.
  2. Set the threshold so the input level on the transfer curve sits 6–10 dB above it.
  3. Set a ratio — gentle (2:1) for vocals and bass, harder (4:1 and up) for drums and aggressive genres.
  4. Watch the GR-over-time plot. If the envelope returns to 0 dB before the next transient hits, your release is short enough.
  5. Set knee to taste — vocals love a wide 6–10 dB knee (smooth); drums prefer a tight 0–3 dB knee (punchy).
  6. Apply makeup gain until the loudest moment matches the input loudness minus 1–2 dB (matched loudness is the point).

How to read the result

  • Transfer curve: above threshold the line bends toward horizontal at a steeper slope for higher ratios. Below threshold the line stays on the diagonal — compression is not applied to quiet parts.
  • Knee: the rounded region around the threshold where the compressor starts easing in. Wider knee = smoother, harder knee = more obvious compression onset.
  • Attack: how fast GR engages after a transient crosses the threshold. Faster attack = more controlled but possibly "sucking" drums. Slower = transient preserved.
  • Release: time to return to zero GR. A release that's too short causes "pumping" on sustained material; too long means GR lingers into the next transient and you lose punch.
  • GR-over-time: this is what 5 dB of GR looks like. If the curve is jittering high, your release is too fast. If it's pinned low, your release is way too slow.

Limitations

The transfer curve is a steady-state model. Real compressors are causal systems — attack, release, RMS window and program-dependent gain all move the actual line around by ±2 dB depending on what came before. Use the curve as a guide, not a contract.

Program-dependent compressors (FET / optical) don't fit the static model well at all. A 1176 with "all buttons in" mode compresses harder the louder the input gets — your transfer curve here can't show that.

RMS vs peak detection changes everything. This tool uses peak detection (very simple). A real VCA compressor on a vocal bus uses RMS windowing which is much slower; the gain reduction envelope will be smoother than what you see here.

Makeup gain is loudness-matched against the input, not loudness-normalised to a target LUFS. If you're mastering, see the LUFS Targeter to set a target ceiling separately.

FAQ

What does "threshold" actually mean if I see dB and dBFS?
On most DAW insert compressors the threshold reads dBFS (i.e. 0 is full scale). Some hardware-style compressors (LA-2A, 1176) are calibrated in absolute dB relative to their internal reference. The number is a value on your signal's range — input 0 dBFS will get compressed above −18 dB threshold with the same math regardless of which scale the knob uses.
How much GR is too much?
Vocals: 4–7 dB max. Drum bus: 3–6 dB. Bass: 2–4 dB (heavy on bass loses the note's body). Master: usually < 2 dB on the bus comp. Anything beyond 10 dB on a single channel is almost certainly overdone — turn the ratio down or the threshold up.
Why does the GR curve look "stepped" when I shorten attack?
The simulation updates at 48 kHz with no smoothing on the attack phase, so very fast attacks (1–2 ms) look like a vertical drop. Real compressors have look-ahead and soft-knee transitions that hide this. Treat the simulation as showing you the envelope shape, not the wave the analogue circuit would actually produce.
Should I bypass the compressor to compare?
Always. The dashed diagonal in the transfer curve represents the bypassed signal — every compressor line sits below it for inputs above threshold. If your compressed version doesn't sound better than the bypassed version in a quick A/B at matched loudness, the settings are wrong (not the choice of compressor).
What's the relationship between ratio and knee?
Ratio controls how much compression is applied above threshold. Knee controls when the compressor starts to apply it. A high ratio + wide knee still sounds smoother than a low ratio + tight knee because the compression intensity changes gradually. For an obvious "compression" sound, do high ratio + narrow knee.
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