Audio

Compression Ratio Calculator

Enter ratio, threshold, and input level — get the exact output level, gain reduction, and a visual transfer curve.

Quick Answer

Above threshold: output = threshold + (input − threshold) / ratio. Below threshold: output = input. Gain reduction = input − output. Add makeup gain to restore level.

Calculate Output

Input Level (dBFS)

Threshold (dBFS)

Ratio (X:1)

Makeup Gain (dB)

Ratio presets

Compressor Output

Output

-15.00

dBFS

Gain Reduction

9.00

dB

Final (w/ Makeup)

-15.00

dBFS

Transfer Curve

-60-48-36-24-120

Input dBFS (X) → Output dBFS (Y). Pink dot = current input/output.

About This Tool

The Compression Ratio Calculator shows exactly what a dynamic range compressor will do to a signal of any given level. Enter your input level, threshold, ratio, and optional makeup gain, and the tool returns the output level, gain reduction, and a visual transfer curve. This is the math that runs inside every compressor plugin and hardware unit on the planet.

How Compression Works

A compressor watches the incoming signal level. When it exceeds a user-set threshold, the compressor starts reducing gain — but not by the full amount. The ratio determines how much. At 4:1, every 4 dB of input above threshold becomes only 1 dB of output above threshold. The signal isn't silenced; it's simply held back. This narrows the dynamic range — peaks come down, average level stays similar, the difference between loud and soft shrinks.

Threshold

Threshold sets the level above which compression engages. Set it too high and only the loudest peaks get touched — gentle "peak control" with minimal coloration. Set it too low and even soft passages get squeezed, producing a pumping, audibly compressed sound. The right threshold depends on your goal: −18 dBFS for transparent leveling on tracking, −24 to −30 dBFS for aggressive mix compression, −1 to −2 dBFS on a final brickwall limiter to catch only the absolute peaks.

Ratio Choices

1.5:1 to 2:1: extremely subtle, almost imperceptible leveling. Use on stereo mix bus, vocal smoothing, or to glue tracks together. 3:1 to 4:1: the classic mixing range. Adds character, controls peaks, makes the source feel more confident. 6:1 to 10:1: aggressive. Reaches into the source, reshapes its envelope. Used on drums for punch, on vocals for in-your-face presence. 10:1 and higher: effectively limiting. The signal is held to threshold no matter how loud it gets.

Attack and Release (Not Modeled Here)

This calculator computes static (steady-state) compression. Real compressors have attack and release times that determine how fast they respond to incoming changes. Fast attacks (0.1-5 ms) catch transients; slow attacks (10-50 ms) let transients through and compress the body of the sound. Fast releases (10-50 ms) sound aggressive and pumping; slow releases (100-1000 ms) feel transparent. The math here gives you the eventual destination level; attack and release determine how quickly you get there.

Soft Knee vs Hard Knee

Hard knee compression (what this calculator models) starts compression abruptly at the threshold. Soft knee compression eases into compression over a range of levels — typical "knee" settings span 5-10 dB on either side of threshold. Soft knees sound more transparent and forgiving, especially at high ratios. Hard knees sound more "present" and intentional. Most compressors offer both modes.

Pair With Other Tools

Use our LUFS Calculator to set loudness targets, the Decibel Distance Calculator for sound pressure math, the MIDI Velocity Calculator for source-side dynamics, the Reverb Time Calculator for room acoustics, or the Audio File Size Calculator when planning sessions.

Frequently Asked Questions

What does compression ratio mean?
Compression ratio is the proportion of input level above threshold to output level above threshold. A 4:1 ratio means that for every 4 dB the input goes over threshold, the output only rises 1 dB. Higher ratios (10:1, 20:1) are aggressive limiting; lower ratios (1.5:1, 2:1) are gentle leveling. The ratio works only on signal above threshold — anything below passes through unchanged.
How is gain reduction calculated?
Gain reduction (GR) = input - output, but only above threshold. If input is -6 dB, threshold is -18 dB, and ratio is 4:1: the input is 12 dB above threshold, the compressor allows 12/4 = 3 dB above threshold, so output = -18 + 3 = -15 dB, and GR = -6 - (-15) = 9 dB. Most compressors display GR as a meter that swings to the right as more compression is applied.
What is makeup gain?
Makeup gain is a level boost applied after compression to compensate for the volume loss caused by gain reduction. If your compressor is pulling down peaks by 6 dB, adding 6 dB of makeup gain restores the peak level — but the average (RMS) level is now louder relative to peaks, which is the whole point of compression. Modern compressors often include 'auto makeup' that adjusts automatically as you change threshold.
What ratio should I use for vocals?
Lead vocals typically use 2:1 to 4:1 with light gain reduction (3-6 dB) for transparent leveling. Aggressive vocal styles (rap, rock screams) might use 6:1 to 10:1 with deeper compression. The threshold matters as much as the ratio — set it so the compressor only kicks in on louder words, leaving quieter syllables untouched. A common technique is to use two compressors in series: a slow leveling compressor, then a faster, more aggressive one.
What's the difference between compression and limiting?
Limiting is just compression with a very high ratio (10:1 or higher, often ∞:1) and a fast attack. The intent shifts: compression shapes dynamics musically; limiting prevents peaks from exceeding a hard ceiling. Brickwall limiters (used at the end of a master) catch only the highest peaks to maximize loudness without clipping. A compressor at 4:1 with 6 dB GR sounds different from a limiter at 20:1 with 6 dB GR, even with similar numerical output.

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