Why did the file get quieter?

Because compression reduces whatever sits above the threshold, and unless the quiet parts happen to fill the gap the average level falls. That is what the make-up gain control is for: add roughly the amount of reduction you can hear, then check the reported average against the original.

What is the knee for?

It softens the transition into compression. With a hard knee the gain reduction arrives the instant a sample crosses the threshold, which is audible on material that sits near the line. A soft knee spreads that change over a few decibels so the compression arrives gradually instead.

How do I make a drum sound punchier?

Slow the attack down. With an attack of ten to thirty milliseconds the gain does not come down until after the initial transient has passed, so the hit keeps its edge while the body behind it is controlled. A fast attack does the opposite and makes the sound denser.

What does pumping sound like and how do I stop it?

It is the level rising and falling audibly with the rhythm, caused by the gain returning too quickly between peaks. Lengthening the release is the first fix; if that dulls the material, a lower ratio with a lower threshold spreads the work over more of the signal.

Is compressing twice the same as compressing harder once?

Not quite. Two gentle stages with different settings tend to sound more transparent than one aggressive stage, because neither has to do very much at any instant. That said the parallel compressor reaches a similar goal by blending a compressed copy with the original.

Audio Compressor

You Might Also Need

Dynamic Range Compressor

Professional-grade audio compression

Multiband Compressor

Compress different frequency bands separately

Parallel Compressor

Blend compressed and dry signals

Audio Limiter

Apply peak limiting to prevent clipping

Audio Compressor reduces the distance between the loudest and quietest parts of a recording, so a mix sits at a more even level. Every parameter of the classic gain computer is exposed, including the knee.

What is Audio Compressor?

Set the six controls, drop a file, and process. The report states the ratio and threshold that applied, the average level before and after, and the make-up gain if any was used.

The controls:

A threshold from forty eight decibels below full scale to full scale, defaulting to minus twenty four.
A ratio from one to twenty to one, in half steps, defaulting to four to one.
A knee from zero to twelve decibels, defaulting to six.
An attack from one to a hundred milliseconds, defaulting to ten.
A release from twenty to six hundred milliseconds, defaulting to a hundred and twenty.
A make-up gain from zero to eighteen decibels, defaulting to zero.

The engine is a static gain computer with a soft knee and an envelope follower. Above the threshold, a sample is reduced according to the ratio: at four to one, four decibels above the threshold produce one decibel of extra output, so the loud parts are pushed back toward the threshold while everything below it passes untouched. The knee is what happens at the boundary. With a hard knee the gain reduction switches on abruptly the moment a sample crosses the line, which is audible on material that hovers there; a soft knee spreads that transition over the chosen number of decibels, so the compression fades in rather than switching. Attack and release set how quickly the gain follows the signal, and they are the controls that decide the character rather than the amount. A slow attack lets the first few milliseconds of a transient through before the gain comes down, which is what makes a drum sound punchy; a fast attack catches the transient and holds it down, which is what makes a part sound dense and controlled. Release governs how quickly the gain returns, and too fast a release on low-frequency material produces audible level flapping. The average level is reported before and after, which is the honest measure of how much the dynamic range actually shrank. Make-up gain is a plain fixed lift applied afterwards, and it is deliberately separate rather than automatic, because only you know whether the reduced file needs bringing back up.

What it does not do:

No automatic make-up gain, so the average level drops unless you add it.
No gain-reduction metering over time, only the average before and after.
One band only, so a single loud low end affects the whole spectrum.
Channels are compressed independently, so a stereo image can shift under heavy compression.
No sidechain input, so it cannot be triggered by another signal.
Output is sixteen bit WAV.

Use it to even out a performance that drifts in level, to add sustain to a bass or a guitar, or to make a mix sit together before a final level stage. When the reduction should be spread across the spectrum instead, the multiband compressor splits the bands first, and when a copy of the signal should be blended back in for a denser result without a fully compressed sound, the parallel compressor does that with one control.

How to use Audio Compressor

Drop an audio file onto the panel and let it decode.
Set the threshold just below the level of the loud passages you want reduced.
Choose the ratio for how much reduction, then the knee and the attack and release for how it behaves.
Press process, read the reported average levels, and add make-up gain if the file is now too quiet.

When to use Audio Compressor vs related tools

Audio Compressor is the general-purpose dynamics stage, useful when a performance varies in level or a part needs more sustain. Dynamic Range Compressor is the way to reach for a specific amount of range reduction, and Multiband Compressor splits the spectrum first so a loud low end does not drag the whole signal down. When the reduction should be triggered by another track, Sidechain Compressor adds that routing.

Privacy & Security

This tool runs entirely in your browser — no data ever leaves your device. There is no server round-trip, no upload, no logging, and no account required. Your input is processed locally using client-side JavaScript and is never stored, transmitted, or accessible to anyone else. When you close the tab, everything disappears.