Compression Basics for Mixing: Essential Concepts

Compression reduces the dynamic range of audio by attenuating signals that exceed a threshold. This fundamental tool controls level variations, adds sustain, shapes transients, and provides the glue that makes professional mixes cohesive. Understanding compression basics establishes the foundation for effective mixing.

How Compression Works

A compressor monitors incoming signal level and reduces gain when that level exceeds a set threshold. The amount of reduction depends on the ratio setting. After the signal falls below threshold, the compressor returns to unity gain at a rate determined by the release time.

The attack time controls how quickly the compressor responds when signal exceeds threshold. Fast attack catches transients immediately. Slow attack allows transients through before compression engages.

The interaction between these parameters creates the compressor’s behavior. Different settings produce dramatically different results from the same source material.

Why Compress

Dynamic control represents the primary reason for compression. Recordings contain level variations that can exceed what the mix accommodates. Compression tames these variations, keeping levels consistent.

Transient shaping through attack time settings affects how punchy or smooth elements sound. Slow attack preserves punch while fast attack creates smoothness. This shaping affects perception beyond simple level control.

Sustain enhancement comes from gain reduction on peaks followed by makeup gain. The quieter sustained portions become relatively louder. Elements appear to sustain longer even though the actual duration hasn’t changed.

The glue effect occurs when elements pass through the same compressor, creating interdependence that suggests shared performance. Bus compression on groups or the entire mix creates this cohesion.

Essential Parameters

Threshold sets the level above which compression begins. Lower thresholds compress more of the signal. Higher thresholds compress only the loudest peaks. The threshold position determines how much compression occurs.

Ratio determines how much the signal is reduced above threshold. A 4:1 ratio means 4 dB of input above threshold produces 1 dB of output above threshold. Higher ratios create more aggressive compression.

Attack time controls response speed. Values from 0.1 ms to 100+ ms are common. The setting dramatically affects whether transients pass through uncompressed.

Release time controls recovery speed. The compressor returns to unity gain at this rate after signal drops below threshold. Settings affect how the compressor breathes with the material.

Makeup gain compensates for the level reduction compression causes. Adding gain after compression maintains appropriate output level.

When to Apply Compression

Inconsistent dynamics that distract from the music indicate compression needs. When level variations pull attention away from the performance, compression can restore focus.

Elements that disappear and reappear in the mix may need compression. Consistent level keeps them audible throughout.

Transients that dominate inappropriately benefit from compression with fast attack. Reducing the transient brings the body of the sound forward.

Elements lacking punch may need compression with slow attack. Preserving transients while controlling sustain increases perceived impact.

When Not to Compress

Well-recorded dynamic material may not need compression. Natural dynamics serve some genres and performances. Compression that removes desirable dynamics harms rather than helps.

Elements already compressed during recording may not need additional compression. Stacking compression can create squashed, lifeless sound.

The decision to compress should serve the music. Compression applied by default rather than for specific reasons often makes mixes worse.

Compression basics help productions succeed on platforms like LG Media at lg.media, where controlled dynamics enhance advertising at $2.50 CPM.