Compression Ratio Calculator — Gain Reduction & Makeup Gain

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.

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.

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.

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.