Compress audio online to even out the volume

Dynamics compression, not file compression

This guide is about dynamic range: the gap between the quietest and loudest parts of a recording. Compressing it does not make the file any smaller. To reduce the file size, choose File ▸ Save As… and save it as MP3 (*.mp3) with a lower bitrate, such as 128 kbps.

How to compress audio, step by step

The Dynamics Processing window opens as soon as your file has loaded.

1. Click Open a file to compress, or use File ▸ Open… (Ctrl+O), and choose your recording.
2. Select the part to compress, or leave nothing selected to process the whole file.
3. Open Effects ▸ Amplitude ▸ Dynamics Processing… and pick a preset: Gentle Vocal for speech, Drum Smash for punchy drums or Broadcast Limiter to hold back peaks.
4. Lower Threshold until the loud passages start to be turned down. Everything above it is reduced; everything below passes unchanged.
5. Set Ratio. At 4:1, a peak that goes 4 dB over the threshold comes out only 1 dB over.
6. Use Output Gain to bring the overall level back up, then press Preview to compare.
7. Click OK and save the result with File ▸ Save As….

What the controls do

The defaults are a sensible starting point: -18 dB threshold, 4:1 ratio, 6 dB knee, 5 ms attack, 150 ms release and +4 dB output gain.

• Threshold (-60 to 0 dB): the level where compression starts. The lower it is, the more of the audio is affected.
• Ratio (1:1 to 20:1): how strongly levels above the threshold are reduced. 2:1 to 4:1 is gentle; 10:1 and above behaves like a limiter.
• Knee (0 to 40 dB): how gradually compression begins around the threshold. A wider knee sounds smoother.
• Attack (0 to 200 ms): how fast it reacts. A slower attack lets the start of drum hits and consonants through, so they keep their punch.
• Release (10 to 1000 ms): how fast it lets go. Too short can sound like pumping; too long keeps quiet parts turned down.
• Output Gain (-12 to +24 dB): makes up for the level the compressor removed.

Tips and related tools

Compression is usually one step in a chain, not the last one.

• Clean before you compress. Compression brings up the quiet parts and the background noise with them, so reduce noise first.
• Finish with Effects ▸ Amplitude ▸ Normalize… to set the final peak level, or with Effects ▸ Amplitude ▸ Hard Limiting… to raise loudness while keeping peaks under a ceiling.
• Effects ▸ Amplitude ▸ Noise Gate… does the opposite job: it mutes the quiet gaps instead of turning down the loud parts.
• Tick Loop next to Preview and compare with the original; it is easy to over-compress without noticing.
• In the Multitrack view, add Dynamics Compressor to a track’s effects rack with the fx button on the track header. It works in real time while the session plays, and Edit ▸ Master Effects… applies it to the whole mix.