What Is Audio Compression?
Audio compression is the process of reducing the difference between the loudest and quietest parts of an audio signal. That difference is called dynamic range.
Dynamic Range
Dynamic range is the difference in volume between the loudest and quietest parts of an audio signal, measured in decibels (dB).
Drag the slider to compress the waveform. Watch how the difference between loud and quiet sections changes — that difference is the dynamic range.
The Core Compressor Controls
A compressor monitors the level of an incoming audio signal. When that level crosses a certain point (called the threshold), the compressor reduces the volume by a specific amount (called the ratio).
The attack controls how quickly the compressor begins reducing the volume after the signal exceeds the threshold, and the release controls how quickly the compressor stops reducing the volume after the signal drops back below it.
The knee determines whether compression is applied gradually or immediately as the signal approaches the threshold.
Because compression lowers the overall volume of the signal, makeup gain is used to bring the compressed signal back up to its original level.
Adjust the controls below to see how each compressor parameter shapes the transfer curve. The curve shows how input levels (horizontal) map to output levels (vertical). Watch the green dot animate a kick drum transient.
At -20 dB, only signals louder than -20 dB trigger compression.
The threshold sets the level where compression begins. Signals below this level pass through unchanged. Lower the threshold to compress more of the signal, or raise it to only catch the loudest peaks.
Why Is Compression Used?
Compression serves several practical purposes in music production and audio engineering.
Controlling dynamics
A vocalist who sings softly in the verse and belts during the chorus can have a dynamic range of 20 dB or more. Without compression, the quiet parts may be inaudible while the loud parts clip or overwhelm the mix. Compression narrows that gap so every word remains audible without any part being too loud.
Adding sustain
On instruments like bass guitar or electric guitar, compression evens out the volume of each note, making the quieter tail end of a note louder relative to the initial pick or pluck. This creates the perception that the note rings out longer.
Shaping transients
A snare drum, for example, has a sharp, fast transient at the moment the stick hits the head. Compression can either preserve that transient for a punchy, aggressive sound or reduce it for a smoother, more controlled feel.
Gluing a mix together
Gentle compression applied to an entire mix or a group of instruments makes the individual elements feel like they belong together rather than sounding like separate recordings stacked on top of each other.
Compressor Example
Below is an example of a compressor with the six core controls: threshold, ratio, attack, release, knee, and makeup gain.
Use the next button to preview the SSL controls on this compressor.
SSL Compressor
Use the next button to preview the SSL controls on this compressor.
Use arrow keys to navigate · Hover over highlighted area to zoom
Summary
A compressor is an audio processing tool that automatically reduces the volume of a signal when it exceeds a set level, called the threshold.
The amount of volume reduction is determined by the ratio, while the attack and release controls determine how quickly the compressor responds to changes in the signal level.
The knee setting controls how gradually or abruptly compression begins as the signal approaches the threshold, and makeup gain restores the overall volume lost during compression.