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Engine Compression Ratio Calculator

Calculate audio compressor output levels from threshold, ratio, and input level. Visualize gain reduction for mixing and mastering.

Use this result well

Inputs that matter
Swept Volume (per cylinder), Clearance Volume (TDC)
Output to expect
Compression Ratio Calculator
  • Check the units and required inputs before comparing results.
  • Keep the assumptions with a copied result so you can reproduce the calculation later.
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Reference & details

How it works

Gain Reduction

When input exceeds threshold, excess level is reduced by ratio. 4:1 ratio means 4 dB input above threshold produces 1 dB output above threshold.

GR = (Input − Threshold) × (1 − 1/Ratio)

Output Level

Below threshold, output equals input (no compression). Above threshold, output increases at 1/ratio of the rate input increases.

Output = Input − GR (when Input > Threshold)

Makeup Gain

Apply makeup gain to restore perceived loudness after compression. Typical: match peak or RMS level to uncompressed signal.

Output_final = Output + Makeup gain

Updated: July 2026

Example Scenarios

Input peaks 10 dB above −20 dBFS threshold → 7.5 dB gain reduction. Peaks compressed from +10 to +2.5 dB relative to threshold.

Light 2:1 on drum bus with −10 dB threshold tames transients without audible pumping — 3 dB GR on loudest hits.

Effectively brick-wall above threshold. Input 5 dB over threshold with 20:1 → 4.75 dB GR, output only 0.25 dB above threshold.

FAQ

2:1 for gentle leveling (bass, mix bus). 4:1–6:1 for vocals and instruments. 8:1–20:1 for limiting and aggressive control. Higher ratio = more compression.

Input level above which compression begins. Set threshold so compressor engages on loudest passages you want to control, not on entire signal.

Soft knee gradually increases ratio near threshold (smooth transition). Hard knee applies full ratio immediately at threshold. Soft knee sounds more transparent.

For transparent compression: 3–6 dB GR on peaks. 10+ dB GR is audible and stylistic. Constant 6+ dB GR suggests threshold too low or ratio too high.

Ratio calculation is steady-state. Attack determines how fast compression engages; release how fast it disengages. They affect perceived compression, not the ratio math.

About Engine Compression Ratio Calculator

Audio compressors reduce dynamic range by attenuating signals above a threshold. Enter input level, threshold, ratio, and knee settings to calculate output level, gain reduction in dB, and effective compression for mixing decisions.