Compression Ratio Explainer

Knowledge Base

How to Use the Compression Ratio Tool

The Compression Ratio Explainer visualizes how compression changes audio dynamics. Enter a compression ratio (4:1, 2:1, etc.), threshold, and sample audio level to see the output level. Critical for understanding compression in mixing and podcast production.

What Is Compression?

Compression reduces the volume of loud parts while leaving quiet parts untouched. A 4:1 ratio means for every 4 dB above the threshold, the output rises only 1 dB. This "glues" a mix together and prevents clipping.

Understanding Ratios

• 2:1 (Gentle): Subtle, musical. For vocals and instruments that need shape without obvious squashing.
• 4:1 (Moderate): Noticeable but natural. Standard for vocal mixing and drums.
• 8:1+ (Heavy): Obvious, pumping, electronic feel. For parallel compression or creative effects.
• ∞:1 (Limiting): Hard ceiling. Output never exceeds the threshold. Protects against clipping.

Compression Settings in Context

Threshold: The dB level where compression starts. Lower threshold = more audio affected.
Attack: How fast compression reacts (fast catches peaks, slow lets transients through).
Release: How fast compression stops after audio drops below threshold.

FAQ

Q: How much compression should I use?
A: 3-6 dB of gain reduction sounds natural. 10+ dB is noticeable and creative. Avoid over-compressing individual tracks.

Q: What's the difference between compression and limiting?
A: Limiting is extreme compression (∞:1) that acts as a safety ceiling. Compression is musical and gradual.

Q: Should I compress before or after EQ?
A: Compress first to control dynamics, then EQ to shape tone. Some engineers reverse this.

What the controls actually do

A compressor reduces level, and only above a point you choose. Below the threshold nothing happens at all. Above it, the signal is reduced by the ratio, so a 4 to 1 ratio means four decibels above threshold become one decibel above threshold. Everything else on the processor modifies how that reduction is applied.

Threshold and ratio work together and are usually adjusted together. A low threshold with a gentle ratio compresses most of the material a little, which evens out a performance transparently. A high threshold with a strong ratio leaves most of the material untouched and catches only the peaks, which controls occasional loud moments without changing the character.

Attack decides how much of the initial transient survives. A fast attack catches the very start of a sound and reduces it, which tames a percussive peak and can also remove the snap making an instrument feel alive. A slower attack lets the transient through and compresses what follows, which usually sounds more natural on speech and on drums.

Release decides how quickly the compressor stops working. Too fast and you hear the background level moving up and down between words, which is the pumping people describe. Too slow and the processor never recovers between phrases, so it holds everything down continuously and the material sounds lifeless.

Watch the gain reduction meter rather than the output. Compression is judged by how much reduction is happening and when, and a few decibels on the loudest moments is usually plenty for speech. Make-up gain then restores the level, which is why heavy compression sounds louder and why comparing settings without matching levels always favours the louder one.

Vocabulary

Threshold. The level above which a compressor starts reducing. Signal below it passes untouched, so the threshold decides how much of a performance is affected at all.

Ratio. How much reduction is applied above the threshold, written as a comparison such as 4 to 1. At 4 to 1, four decibels of input above threshold produce one decibel of output above it.

Attack and release. How quickly the compressor begins reducing once the threshold is passed, and how quickly it stops afterwards. Together they determine whether compression sounds transparent or audibly pumping.

Make-up gain. Level added after compression to compensate for the reduction. Necessary for a fair comparison, because a louder version almost always sounds better in an unmatched test regardless of the settings.

Worked example: gain reduction above a -18 dB threshold

A compressor leaves quiet sound alone and turns down what rises above the threshold. Gain reduction equals the amount over the threshold times 1 minus 1 divided by the ratio. The output level is the input level minus that reduction. The table uses the tool's default threshold of -18 dB and four of its ratio settings.

At 4:1, a signal 12 dB over the threshold comes out 3 dB over it. That is what the ratio names: for every 4 dB in above the threshold, 1 dB comes out. At 20:1 the compressor holds the level almost flat at the threshold, which is how a limiter behaves. A signal at or below -18 dB passes through unchanged at every ratio.

Vocabulary

Threshold. The level above which a compressor starts turning the signal down. Sound below the threshold passes through unchanged. Setting it lower means more of the signal gets compressed.

Gain reduction. The number of decibels the compressor turns the signal down at a given moment. The compressor meter shows it, and it equals the amount over the threshold times 1 minus 1 divided by the ratio.