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How Well Do You Know Compression?

20 questions on what a compressor actually does, where the technology came from, and when to reach for one. No time limit, no email, answers at the end.

20 questions ≈ 8 minutes Answers explained

0 of 20 answered

01

THE BASICS

What does an audio compressor do?

02

THE BASICS

What is dynamic range?

03

THE BASICS

Does a compressor make audio louder or quieter?

04

THE BASICS

What does the threshold control set?

05

THE BASICS

A ratio of 4:1 means what, exactly?

06

REACHING FOR ONE

Which of these is not a job for a compressor?

07

REACHING FOR ONE

You want to keep the snap on a snare. Fast attack or slow?

08

REACHING FOR ONE

What is a limiter, really?

09

REACHING FOR ONE

What does a gate do that a compressor doesn't?

10

UNDER THE HOOD

What does a sidechain or key input let you do?

11

UNDER THE HOOD

RMS detection responds to what?

12

UNDER THE HOOD

What is parallel compression?

13

UNDER THE HOOD

A de-esser is essentially which of these?

14

UNDER THE HOOD

A VCA can turn a signal down as well as up. How, if it’s an “amplifier”?

15

UNDER THE HOOD

If a compressor narrows dynamic range, what does an expander do?

16

dbx HISTORY

Who founded dbx in 1971?

17

dbx HISTORY

When did audio compression first appear?

18

dbx HISTORY

dbx’s OverEasy describes what?

19

dbx HISTORY

The dbx 160 became a studio standard largely because of what?

20

dbx HISTORY

The dbx 160 became famous throughout the recording industry. Which of these recordings actually used it?

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All 20 answers

01

What does an audio compressor do?

Reduces the dynamic range of a signal

A compressor’s core job is dynamic range reduction — turning down whatever crosses the threshold so the loudest and quietest parts of a signal sit closer together. Everything else a compressor gets credit for — glue, punch, perceived loudness — is a side effect of that one basic move.

02

What is dynamic range?

The spread from the quietest to the loudest part of a signal

Dynamic range is simply how far a signal swings between its softest and loudest moments — a whisper-to-scream vocal has a wide dynamic range, a single sustained synth pad has almost none. Compression narrows that spread rather than eliminating it.

03

Does a compressor make audio louder or quieter?

Quieter — it only ever turns signal down

A compressor only reduces gain, and only above the threshold. It ends up sounding louder because of the makeup gain applied afterwards, which lifts the whole signal once the peaks are under control.

04

What does the threshold control set?

The level above which compression starts

Below the threshold nothing happens. Above it, gain reduction is applied at whatever ratio you have set.

05

A ratio of 4:1 means what, exactly?

4 dB above threshold comes out 1 dB above

Ratios describe what happens to signal past the threshold. At 4:1, an input 8 dB over threshold leaves 2 dB over.

06

Which of these is not a job for a compressor?

Correcting a room’s frequency response

Room response is an equalization problem — that is what a graphic or parametric EQ is for. The other three are all everyday compressor work.

07

You want to keep the snap on a snare. Fast attack or slow?

Slow — let the transient through, then clamp

A fast attack grabs the initial spike and dulls the hit. A slower attack lets the transient pass before gain reduction arrives, so the snare keeps its front edge.

08

What is a limiter, really?

A compressor with a very high ratio

Ratios of 10:1 and up behave as a ceiling, and infinity:1 is a brickwall. dbx units such as the 166xs put both jobs in one box for this reason.

09

What does a gate do that a compressor doesn't?

Attenuates signal below the threshold

A compressor works on what is too loud, a gate on what is too quiet — silencing bleed and room noise between phrases. That is why they so often ship in the same chassis.

10

What does a sidechain or key input let you do?

Trigger compression from a different signal

Feeding the detector from another source is how ducking works: the paging mic controls the gain reduction applied to the music. Mix engineers lean on the same trick to make room in a busy mix — sidechaining a bass to the kick so the two don't fight for the same low end, or ducking supporting parts whenever the lead vocal comes in so it always cuts through.

11

RMS detection responds to what?

Average energy over a short window

RMS — root mean square — squares the signal, averages that over a short window, then takes the square root back to a level; the result tracks average energy rather than any single peak, which is closer to how we perceive loudness. Peak detection catches instantaneous spikes instead. dbx built its reputation on accurate RMS detection.

12

What is parallel compression?

Blending a heavily compressed copy back under the dry signal

Sometimes called New York compression. You keep the dry transients and lift the quiet detail underneath, rather than squashing one signal harder.

13

A de-esser is essentially which of these?

A compressor that only listens to a narrow band

Frequency-dependent compression: the detector listens to the sibilant range and ducks the signal when it gets loud there. The dbx 520 in the 500 Series does exactly this.

14

A VCA can turn a signal down as well as up. How, if it’s an “amplifier”?

Its gain can be set above or below unity — the same circuit that boosts can just as easily cut

A VCA’s gain is set by a control voltage, and that voltage can push gain above unity (boost) or below it (cut) — “amplifier” just means a circuit that scales a signal, and the scale factor doesn’t have to be greater than one. In a compressor, the detector’s control voltage pulls the VCA’s gain down as the signal crosses the threshold; the exact same circuit that could just as easily turn a signal up is instead being told to turn it down.

15

If a compressor narrows dynamic range, what does an expander do?

Makes quiet signal quieter, widening the gap between loud and quiet

A compressor narrows dynamic range by turning down what’s loud. An expander does the opposite: it turns down what’s already quiet, below its own threshold, which widens the gap between the loudest and softest parts. Push that ratio to the extreme and expansion becomes gating — which is why dbx pairs the two in one channel on units like the 266xs. That same compress-then-expand idea became the basis of dbx’s famous noise reduction systems, used to quiet multi-track tape recordings for decades.

16

Who founded dbx in 1971?

David E. Blackmer

Blackmer founded dbx in 1971. He is best known for the Blackmer VCA (Voltage Controlled Amplifier) and for accurate RMS level detection — the two building blocks behind the company’s compressors and noise reduction.

17

When did audio compression first appear?

1930s, in broadcast limiters

Broadcast engineers were building limiters to protect transmitters well before compression became a studio tool. dbx improved on it from there, engineering more accurate and affordable compressors that became a staple in every recording studio and some of the most popular processors in the signal chain ever since.

18

dbx’s OverEasy describes what?

A soft knee — compression easing in around the threshold

Instead of a hard corner at the threshold, OverEasy bends into compression gradually, which is much harder to hear working. It became one of the most recognizable dbx features.

19

The dbx 160 became a studio standard largely because of what?

Its VCA and RMS detection

The combination of a low-distortion VCA and true RMS detection let it hold a signal firmly without the artifacts engineers were used to hearing. It is still the reference point for the family.

20

The dbx 160 became famous throughout the recording industry. Which of these recordings actually used it?

All of the above

All three really did use the dbx 160: engineer Val Garay put it on guitar for Kim Carnes’ Grammy-winning “Bette Davis Eyes,” it was his very first use of the unit — on drums — for Linda Ronstadt’s Hasten Down the Wind, and decades later Michael Brauer crushed a bass channel through one on Coldplay’s “Violet Hill.” Same compressor, more than three decades of hit records.