What Is Audio Compression?
Compression is one of the most fundamental tools in audio production. Every recorded song, podcast, film score, and broadcast that reaches your ears has passed through at least one compressor.
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.
Drag the slider to compress the waveform. Watch how the difference between loud and quiet sections changes — that difference is the dynamic range.
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. When the signal drops back below the threshold, the compressor stops reducing the volume and lets the signal return to its original level.
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.
The Core Compressor Controls
Every compressor, whether hardware or software, shares the same fundamental controls. The names and layout may vary slightly between different models, but the underlying function of each parameter remains consistent.
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.
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 reduces the dynamic range of an audio signal by lowering the volume of sounds that exceed a set threshold. The six core controls, threshold, ratio, attack, release, knee, and makeup gain, work together to determine when compression starts, how much is applied, how quickly it responds, and how the overall level is restored.
Understanding these controls provides the foundation for making informed decisions about dynamic processing in any audio production context, from recording a single vocal to mastering a completed mix.
Next up: Types of Compressors — Audio Compression Part 2 covers VCA, FET, optical, vari-mu, bus compressors, and modern digital designs.