Compressor Gain Reduction Calculator
Understanding how a compressor affects signal level is essential for mixing and mastering. A compressor applies a ratio to any signal that exceeds the threshold: for every N dB above the threshold, the output only rises by 1 dB (ratio N:1). This calculator shows the exact output level in dBFS and the gain reduction applied for any input level, threshold, and ratio. Enter these three values to instantly see how much the compressor is working and what the output level will be.
Compressor gain reduction formula
If input <= threshold: output = input (no compression)
If input > threshold:
excess = input - threshold
output = threshold + excess / ratio
gain_reduction = input - output
The compressor only acts on signal exceeding the threshold. The gain reduction is the difference between the uncompressed input and the compressed output. If the input is below the threshold, there is no gain reduction and output equals input.
Common compressor ratio settings
- 1.5:1 to 2:1: very gentle, barely audible, for subtle glue compression on buses.
- 3:1 to 4:1: moderate compression, common for drums, bass, and vocals.
- 6:1 to 8:1: heavy compression for drums buses and aggressive limiting.
- 10:1 to 20:1: hard limiting, often used to prevent clipping.
- Infinity:1: brick-wall limiting - output cannot exceed the threshold.
Compressor gain reduction: frequently asked questions
How does a compressor calculate gain reduction?
A compressor attenuates signal above the threshold by the ratio. Amount above threshold (in dB) = input - threshold. Compressed amount = amount above threshold / ratio. Output = threshold + compressed_amount. Gain reduction = input - output.
What does a 4:1 ratio mean?
A 4:1 ratio means for every 4 dB the input goes above the threshold, the output only rises by 1 dB. If the input is 8 dB above threshold, the output is only 2 dB above it. The gain reduction is 6 dB.
What is the difference between threshold and knee?
Threshold is the level above which compression begins. Knee describes how abruptly compression starts: a hard knee applies full ratio immediately at the threshold; a soft knee gradually applies the ratio over a range of dB either side of the threshold for a smoother transition.
How much gain reduction is typical?
For transparent compression: 2 to 4 dB gain reduction. For moderate dynamics control: 4 to 8 dB. For heavy compression (pumping or limiting): 8 to 20+ dB. More than 20 dB gain reduction is typically limiting, not compression.
What is make-up gain?
Because a compressor reduces the overall level, make-up gain (or output gain) is applied after compression to restore the average level. A good starting point for make-up gain is approximately half the amount of gain reduction applied.
Official sources
- Audio Engineering Society (AES): aes.org - dynamic processing and compressor standards.
- NIST (nist.gov): NIST TN 1297 - decibel measurement guidelines.
Reviewed by the CalculatorHub team, edited by James Graham, 15 June 2026. See our methodology.