Compression Ratio Calculator
Compression Ratio Calculator
Enter the input level, threshold, ratio and knee width. See the output level, how many dB of gain reduction you get, the makeup gain to match loudness, and the transfer curve.
Soft knee starts compressing gently below the threshold and reaches the full ratio above it. Makeup gain shown restores the peak to the input level; for loudness matching use less, usually about half the gain reduction.
What the ratio actually does
A compressor's ratio describes how much the output rises for every decibel the input goes over the threshold. At 4:1, a signal 8 dB above the threshold comes out only 2 dB above it; the other 6 dB is gain reduction. Ratios of 2:1 to 4:1 are gentle control, 8:1 to 10:1 is heavy, and anything above about 20:1 is limiting. This calculator shows the exact output level and gain reduction for your settings and draws the transfer curve so you can see the knee.
Hard versus soft knee
With a hard knee nothing happens until the threshold, then the full ratio applies. A soft knee of 6 to 12 dB starts reducing gain gradually from below the threshold, which sounds smoother on vocals, bass and the mix bus. Drums and limiting usually want a hard knee.
Makeup gain
Compression turns peaks down, so the track sounds quieter. Adding makeup gain equal to the gain reduction restores the peak level; adding about half of it tends to match perceived loudness, which is the fair way to judge whether the compression helps.
FAQ
What does a 4:1 compression ratio mean?
For every 4 dB the input rises above the threshold, the output rises 1 dB. The remaining 3 dB is gain reduction.
How much gain reduction is normal?
2 to 4 dB on buses and gentle sources, 4 to 8 dB on vocals and drums, 10 dB or more only on parallel or effect compression.
What is the difference between a compressor and a limiter?
A limiter is a compressor with a very high ratio (20:1 to infinity) and a fast attack, used to stop peaks at a ceiling rather than to shape dynamics.
How do I set makeup gain correctly?
Bypass the compressor and match the loudness, not the peaks. In practice about half the gain reduction value is a good starting point.
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