What Is Compression Ratio?

Compression ratio is how hard a compressor turns down audio once it crosses the threshold — it decides how much of a loud peak actually gets reduced.

The ratio is written as N:1, describing an input-to-output relationship: for every N decibels the input goes above the threshold, the output is allowed to rise only 1 dB. So at 4:1, an input that lands 8 dB over the threshold comes out just 2 dB over. At 2:1 that same 8 dB over becomes 4 dB; at 8:1 it comes out only 1 dB over. The higher the first number, the flatter the loud parts get.

The common ratios

Most settings fall somewhere on a ladder from gentle to aggressive:

• 2:1 — subtle "glue," light leveling. You barely hear it working. Good on a mix bus.
• 4:1 — moderate and the everyday workhorse, especially on vocals.
• 8:1 to 10:1 — aggressive; clearly audible control, used to tame stubborn peaks.
• Above ~10:1 to 20:1 — this is where limiting begins. A limiter is essentially a compressor with a very high ratio; a brick-wall limiter behaves like ∞:1, letting almost nothing past the ceiling.

Ratio never works alone. The threshold sets when compression starts (which signals are loud enough to be acted on); the ratio sets how much those signals are reduced. Attack and release shape how quickly the compressor grabs and lets go of each transient — they change the feel of the compression, but they are separate controls from the ratio.

Why the ratio you pick matters

Choosing a ratio is really choosing how much dynamic range to trade away. Low ratios (2:1) preserve the natural loud-and-quiet contrast of a performance. High ratios (8:1 and up) flatten it, making everything sit at a more constant level. So let the task guide the number: even out a moving vocal with a moderate 3:1–4:1, glue a mix bus with a gentle 2:1, or clamp peaks hard before mastering with 8:1 or a dedicated limiter.

You can try all of this in the browser with our free browser compressor — it has a ratio control alongside threshold, attack, release, knee, and makeup gain, plus vocal, master, and aggressive presets. It is 100% client-side, so your audio never leaves your device, and there is no account or upload.

To go deeper, see what audio compression is for the parent concept, compressor attack and release settings for the timing controls, dynamic range for what the ratio trades away, and how to use a compressor for a step-by-step walkthrough. When a ratio gets extreme, read compressor vs limiter and what a limiter is.

Frequently asked questions

What ratio should I use for vocals?

Start around 3:1 to 4:1 for most vocals. That is enough to even out the loud and soft words so the performance sits steadily in a mix, without squashing the natural expression out of it. If a vocal is very dynamic, push to 6:1 or higher, or use a second, gentler compressor in series rather than one heavy stage.

What's the difference between a 4:1 and an 8:1 ratio?

Both reduce anything above the threshold, but 8:1 clamps peaks roughly twice as tightly. An input 8 dB over the threshold comes out 2 dB over at 4:1, but only 1 dB over at 8:1. So 4:1 keeps more of the original dynamics and sounds more transparent, while 8:1 clamps peaks down more tightly and sounds noticeably more controlled.

At what ratio does a compressor become a limiter?

There is no hard cutoff, but ratios of about 10:1 to 20:1 and above are generally considered limiting. At those settings almost nothing is allowed past the threshold, so the compressor stops gently leveling and starts acting as a ceiling. A true brick-wall limiter takes this to the extreme, behaving like an ∞:1 ratio so the signal never exceeds a set peak.