Five Compressor Settings

What threshold, ratio, attack, release and knee each change, and how to hear the difference on one loop.

Related

CompressorSidechainBusDrum Kit

The question

The instruction to compress it hides at least five settings. Move only the threshold and the sound turns flat; match attack and release and compression starts to hold the performance instead of pressing it down.

How it works

A detector reads the input level and, above the threshold, scales gain by the ratio. At 2 to 1, 10 dB over the threshold leaves 5 dB. The knee decides whether gain reduction begins abruptly or gradually. Attack and release are speeds of gain change, not speeds of the sound. Makeup gain restores the overall level, without which compression only seems quieter.

Settings and what you hear

For a vocal, start near minus 20 dB with 3 to 1, attack 10 to 30 ms to let consonants through, release 80 to 200 ms to follow phrases. Attack faster than 5 ms removes the beater click of a drum; a very short release pumps with the bass. A soft knee suits a bus; a hard knee suits taming a single transient.

What to listen for

Play a drum loop and listen to the edge of the snare, then pull attack from 30 ms to 1 ms. Next, with bass and drums together, hear whether the whole picture dips and recovers with every bass note.

Common misconceptions

That compression is a volume knob; that a higher ratio means louder; that the fastest attack is always safest.

Sources

• Giannoulis, Massberg and Reiss, Digital Dynamic Range Compressor Design, JAES 2012 — background checked, not quoted
• Huber and Runstein, Modern Recording Techniques, dynamics chapter — typical ranges checked, not quoted

Used for fact-checking only; all prose is original.