Even out the volume of voice recordings, podcasts and music. Shape the compression with threshold, ratio, attack, release, knee and makeup gain, or switch to a look-ahead brickwall limiter, and watch the gain reduction while you listen to an A/B preview.
Last updated:
Preview: demo mix
Input dB → · Output dB ↑ · orange line: threshold
GR
0.0
OriginalProcessedGain reduction
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How to use the Audio Compressor and Limiter
Listen to the demo or drop your own files on the box; the first file opens in the preview automatically.
Pick a preset such as Podcast / voice leveler, then fine-tune threshold, ratio, attack and release.
Press Play processed and watch the gain reduction meter. Use A/B to switch to the original at the same position.
Switch to Limiter if you only want to catch peaks or make a track louder up to a fixed ceiling.
Choose WAV or MP3, press Compress files and download each result or all of them as a ZIP.
How the compressor calculates gain
For every sample the level detector measures the input in dBFS (RMS over about 10 ms, or the instantaneous peak). The gain computer then follows the standard static curve for threshold T, ratio R and knee width W:
below the knee, 2(x − T) < −W: output = x (no compression)
inside the knee, |2(x − T)| ≤ W: output = x + (1/R − 1)(x − T + W/2)² ÷ (2W)
above the knee, 2(x − T) > W: output = T + (x − T) ÷ R
The difference between input and output is the gain reduction. It is smoothed with separate attack and release time constants (α = e−1/(τ·fs)), applied to both channels together, and finally the makeup gain is added. Example: with T = −20 dB and R = 4:1, a peak at −8 dB is 12 dB over the threshold and comes out at −20 + 12 ÷ 4 = −17 dB, a gain reduction of 9 dB.
Starting points
Material
Threshold
Ratio
Attack
Release
Target GR
Podcast / spoken word
−24 to −18 dB
3:1 to 4:1
2–10 ms
80–200 ms
3–8 dB
Lead vocal (gentle)
−18 dB
2:1
10 ms
200 ms
2–4 dB
Drums (punch)
−22 dB
4:1
20–30 ms
60–100 ms
4–6 dB
Mix bus glue
−16 dB
1.5:1 to 2:1
30 ms
200–300 ms
1–3 dB
Acoustic / classical
−14 dB
1.5:1
20 ms
400 ms
1–2 dB
Final peak limiting
Limiter, ceiling −1 dB
lookahead 2–5 ms
50–150 ms
0–4 dB
Tips
Compare with A/B at equal loudness (Auto makeup on). Louder almost always sounds "better", so judge the dynamics, not the volume.
If you hear pumping or breathing, lengthen the release or raise the threshold. If transients sound dull, lengthen the attack.
Crest factor (peak minus RMS) shows how dynamic the audio is: uncompressed speech and acoustic music often sit around 15–20 dB, heavily limited masters below 10 dB.
The loudness range in the statistics is the spread between quiet and loud passages (10th to 95th percentile of 400 ms RMS blocks). Compression mainly shrinks this number; limiting mainly shrinks the crest factor.
A ceiling of −1 dBFS leaves room for MP3 and AAC encoding, which can push peaks slightly above the original.
Frequently asked questions
What does an audio compressor do?
A compressor turns down the volume whenever the signal rises above the threshold. With a 4:1 ratio, every 4 dB the input goes above the threshold comes out as only 1 dB above it. Loud parts become quieter relative to soft parts, and makeup gain then raises the whole signal so it sounds louder and more even.
What is the difference between a compressor and a limiter?
A limiter is a compressor with an infinite ratio and a very fast attack: the output can never exceed the ceiling. This tool's limiter also looks ahead a few milliseconds so it can lower the gain before a peak arrives, which avoids clipping and distortion. Compressors shape dynamics gently; limiters set a hard maximum.
Which settings are good for a podcast or voice?
A common starting point is a threshold around −24 to −18 dB, a ratio of 3:1 to 4:1, attack of 2 to 10 ms, release of 80 to 200 ms, RMS detection and a soft knee. Aim for 3 to 8 dB of gain reduction on loud words. Normalize the result afterwards to −16 LUFS for podcasts.
What do attack and release mean?
Attack is how quickly the compressor reacts after the signal crosses the threshold; release is how quickly it lets go when the signal falls. A slow attack lets the start of drum hits and consonants through, which keeps punch. A very fast release can cause audible pumping, while a slow release can hold quiet passages down.
What is the knee?
The knee is the region around the threshold where compression fades in. With a hard knee (0 dB) the full ratio applies exactly at the threshold. With a soft knee of, say, 6 dB, compression starts 3 dB below the threshold and reaches the full ratio 3 dB above it, which sounds smoother.
What is gain reduction?
Gain reduction (GR) is how many decibels the compressor or limiter is turning the signal down at each moment. The meter shows it live during playback, and the orange curve above the waveform shows it for the whole clip, with the maximum and average values in the statistics.
Are my files uploaded?
No. Decoding, compression and encoding all run in your browser with the Web Audio API and JavaScript, so your audio never leaves your device.
Are all the tools on FreeToolCabin tested for quality and accuracy?
Yes! Every tool on our site undergoes automated Q/A testing in real browser environments to ensure high precision, correct output, and zero errors. If you happen to spot a bug or have a suggestion, please contact us at [email protected] and our team will review it right away.