How does compression ratio work?

Compression ratio determines how much a signal above the threshold is reduced. At 4:1, for every 4 dB the input exceeds the threshold, only 1 dB comes through. So if the threshold is -18 dBFS and the input is -6 dBFS (12 dB over), the output is -18 + (12/4) = -15 dBFS, a 9 dB reduction.

What compression ratios are used for different purposes?

Gentle compression: 1.5:1 to 2:1 (mix bus, mastering). Moderate: 3:1 to 4:1 (vocals, bass). Heavy: 6:1 to 10:1 (drums, aggressive vocals). Limiting: 10:1 to infinity:1 (peak limiting, broadcast). Lower ratios sound more transparent.

What is makeup gain and how much do I need?

Makeup gain compensates for the volume lost during compression. This calculator's Suggested Makeup brings the compressed peak up to the Makeup Gain Target (default 0 dBFS), i.e. makeup = Target − Output. An alternative, loudness-matching approach is to set makeup gain equal to the average gain reduction so the compressed signal has a similar perceived loudness to the uncompressed signal, which makes A/B comparison more accurate. The two methods give different numbers — peak-matching restores headroom, loudness-matching restores perceived level.

What happens below the threshold?

With a hard knee (knee width = 0, the default), signals below the threshold pass through unaffected (gain reduction = 0 dB) and only the portions of the signal that exceed the threshold are compressed. With a soft knee, gentle compression begins within half the knee width below the threshold, so a signal slightly under the threshold can still receive a small amount of gain reduction. Either way, threshold setting is critical — it determines how much of the signal is affected by the compressor.

AudioCalcs

Compression Ratio Calculator — Gain Reduction & Makeup Gain

Calculate output level, gain reduction and makeup gain for a given compression ratio.

Input Level

Enter the input level

Threshold

Level at which processing begins

Ratio

Compression ratio (e.g. 4:1)

How We Calculate This

Output Level

If input > threshold: Output = Threshold + (Input − Threshold) / Ratio

If input ≤ threshold: Output = Input (no compression)

Gain Reduction

GR = Input − Output

Soft Knee

With a non-zero knee width W, the transition is smoothed within ±W/2 of the threshold using the quadratic gain computer (Giannoulis, Massberg & Reiss, JAES 2012): Output = Input + (1/Ratio − 1)·(Input − Threshold + W/2)² / (2W). A knee of 0 dB gives a hard knee.

Makeup Gain

Set to Target − Output so the compressed peak reaches the Makeup Gain Target (default 0 dBFS).

Frequently Asked Questions

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Last updated: February 2026

All calculations are estimates based on standard formulas. Always verify results for critical applications.