A compressor's threshold, ratio, attack, and release determine when and how much gain reduction is applied

A compressor reduces dynamic range by attenuating peaks above a threshold. Core parameters: Threshold (dB) — where compression begins. Compression ratio — how many dB of input increase produce 1 dB of output increase (4:1 means 4 dB above threshold yields 1 dB at output). Attack time — how quickly gain reduction reaches the target ratio after the signal exceeds threshold. Release time — how quickly gain returns to unity when signal drops. A critical misconception: release does not happen only when the signal drops below threshold — it occurs with every decrease in amplitude, even while signal stays above threshold. Makeup gain compensates for the overall level reduction.

Examples

Voice-over: threshold -18 dB, ratio 3:1, fast attack/release smooths peaks. Guitar: ratio 8:1, slow attack lets the initial pick through, compresses sustain. Limiter: ratio infinity:1 at -1 dB prevents clipping. A de-esser uses a bandpass sidechain plus compression to reduce sibilance.

Assessment

A compressor is set to threshold -10 dB, ratio 4:1. An input peak reaches -2 dB. What is the output level? Explain attack time and why too-fast attack ruins a drum sound.