Free Online Audio Compressor
Professional audio compression with full manual control over threshold, ratio, attack, and release. Upload any audio file, compress dynamics precisely, and download the result. Runs entirely in your browser.
Upload a file · Boost, EQ, export · 100% in your browser
Audio compression is one of the most misunderstood yet essential tools in audio production. At its core, a compressor does one thing: it reduces the dynamic range of an audio signal by making loud parts quieter relative to quiet parts. When a podcaster's voice jumps from a whisper to a shout, the compressor catches the loud syllables and pulls them down. When a guitarist's picking dynamics vary from barely audible to full-force strumming, the compressor evens the levels. The result is audio that sits at a more consistent volume — easier to listen to, easier to mix, and easier to hear in noisy environments.
The problem with most free online compression tools is that they hide the controls. They offer a single "compression amount" slider or a vague "normalize" button that applies unknown settings behind the scenes. For podcasters trying to match broadcast loudness standards, musicians preparing tracks for distribution, or content creators polishing voiceovers, this black-box approach is useless. You need to know when compression engages (threshold), how much it reduces the signal (ratio), how quickly it reacts (attack), and how quickly it releases (release). These four parameters interact in complex ways, and getting them right is the difference between transparent, professional compression and the pumping, breathing artifacts that mark amateur audio.
Hearably Studio Pro gives you full manual control over all four compression parameters across a 3-band multiband compressor. The multiband architecture splits the audio at 250 Hz and 4 kHz using a phase-aligned Linkwitz-Riley crossover, then applies independent compression to the low, mid, and high frequency bands. This means you can compress boomy bass without affecting vocal clarity, or tame harsh sibilance in the highs without squashing low-end warmth. Each band has its own threshold (the level at which compression begins), ratio (how aggressively the signal is reduced), attack time (how fast the compressor reacts to peaks), and release time (how quickly it returns to unity gain after the signal drops below threshold).
Threshold is arguably the most important parameter. Set it too low (e.g., -40 dB) and the compressor engages on virtually everything, squashing dynamics and producing a lifeless, over-compressed sound. Set it too high (e.g., -10 dB) and it only catches the loudest peaks, barely affecting the overall dynamics. For spoken word, a threshold between -24 dB and -18 dB with a 3:1 ratio is a solid starting point. For music, -20 dB to -12 dB with a 2:1 to 4:1 ratio works well. The attack time controls whether transients (drum hits, consonants, pick attacks) punch through before compression engages — faster attack (5-10 ms) catches transients, slower attack (30-50 ms) lets them through for a more dynamic sound.
Hearably Studio's compressor uses RMS (Root Mean Square) level detection rather than peak detection. RMS measures the average energy of the signal over a short window, which more closely corresponds to how our ears perceive loudness. This produces smoother, more musical compression compared to peak-detecting compressors that react to individual sample values and can sound choppy on complex material. After compression, optional makeup gain restores the overall level — bringing the quiet parts up now that the loud parts have been controlled. Combined with the look-ahead limiter that prevents any post-gain peaks from clipping, the full chain delivers broadcast-quality dynamic control in a free browser tool.
How Audio Compression Works — Threshold, Ratio, and Beyond
A compressor continuously monitors the input signal level and applies gain reduction when that level exceeds the threshold. The amount of reduction is determined by the ratio. At a 4:1 ratio, for every 4 dB the input exceeds the threshold, the output only increases by 1 dB — the other 3 dB are "compressed" away. At the extreme, an infinity:1 ratio is a limiter — nothing gets through above the threshold. The relationship between input level, threshold, and ratio defines the transfer curve (or knee curve) that maps input dB to output dB.
Hearably Studio's compressor uses a soft knee design, where the transition from uncompressed to compressed is gradual rather than an abrupt angle at the threshold point. This produces more transparent-sounding compression because the ratio ramps up smoothly as the signal approaches and exceeds the threshold, rather than slamming from 1:1 to the full ratio instantaneously. The soft knee width is proportional to the ratio — higher ratios get a wider knee to compensate for more aggressive gain reduction.
The attack and release times control the compressor's envelope follower — the circuit (or in our case, the algorithm) that tracks the signal level over time. Attack time determines how many milliseconds it takes for the compressor to reach full gain reduction after the signal exceeds the threshold. Release time determines how long it takes to return to unity gain after the signal drops below threshold. The level detection uses RMS averaging over a configurable window (typically 10-50 ms), which measures the signal's energy rather than instantaneous peaks. RMS detection produces smoother compression that responds to the perceived loudness of the signal, avoiding the choppy artifacts that peak detection can produce on complex material with dense harmonic content. After the multiband compressor, makeup gain and the look-ahead limiter complete the chain.
How to get the best audio on Free Online Audio Compressor
Start with threshold — it is the most impactful control
Set your ratio to 3:1 first, then sweep the threshold downward while listening. You will hear the compressor engage when the audio starts to sound more "controlled" and even. For podcasts, start around -20 dB. For music, start around -15 dB. Adjust from there based on how much gain reduction sounds right.
Use slow attack for music, fast attack for speech
A slower attack time (20-50 ms) lets the initial transient of drums, picks, and plucks through before compression engages — preserving the "punch" and liveliness of musical performances. For speech and podcasts, a faster attack (5-15 ms) catches the plosives and level jumps that make spoken word fatiguing to listen to.
Match release to the tempo of the material
If the release is too fast, you hear the gain "breathing" between syllables or notes. If it is too slow, the compressor stays engaged through quiet passages and squashes the next transient. For speech, 100-200 ms works well. For rhythmic music, time the release so it recovers before the next beat hits.
Use multiband compression for complex material
Single-band compression applies the same gain reduction across all frequencies — a loud bass note triggers compression that also ducks the vocals. Hearably's 3-band multiband compressor (split at 250 Hz and 4 kHz) lets you compress bass, mids, and highs independently. This is essential for mastering and for fixing recordings with unbalanced frequency content.
Apply makeup gain after compression
Compression reduces the level of loud passages, which lowers the overall perceived loudness. Makeup gain compensates by boosting the entire signal after compression. The look-ahead limiter ensures this post-compression boost never clips. This is how professional mastering achieves "loud but controlled" audio.
Use A/B preview to avoid over-compression
It is easy to keep adding compression until the audio sounds "better" — louder and more present. But over-compressed audio sounds lifeless, pumpy, and fatiguing. Pro users can toggle A/B preview to compare the compressed result against the original and ensure dynamics are controlled but not destroyed.
Built for this exact use case
Full Manual Controls
Adjust threshold, ratio, attack, and release for each of the 3 bands independently. No black-box "auto-compress" — you see and control exactly what the compressor is doing to your audio.
3-Band Multiband Compression
Linkwitz-Riley crossover splits audio at 250 Hz and 4 kHz. Compress boomy bass without affecting vocal clarity. Tame harsh highs without squashing low-end warmth. Phase-aligned reconstruction.
RMS Level Detection
The compressor responds to average signal energy, not instantaneous peaks. This produces smoother, more musical compression that matches how human ears perceive loudness — no choppy artifacts on complex material.
Look-Ahead Limiter Safety Net
After compression and makeup gain, the look-ahead limiter catches any peaks that would clip. Push compression hard, add makeup gain aggressively — the limiter guarantees zero distortion in the final output.
Choose your method
Different situations call for different tools. Hearably gives you both.
Chrome Extension
Enhance audio live while you stream. The extension intercepts your tab's audio and processes it in real-time — volume boost, EQ, presets — without downloading anything.
- Streaming on Free Online Audio Compressor, Netflix, Spotify
- Video calls on Zoom, Meet, Teams
- Any website with audio
- When you want instant, always-on enhancement
Free Online Studio
Upload an audio or video file, apply volume boost + 10-band EQ, preview in real-time, then download the enhanced WAV. Your file never leaves your browser.
- Downloaded videos or music files
- Podcast episodes you want to boost before sharing
- Voice recordings, lectures, interviews
- When you need a permanently enhanced file
Pro tip: Use a YouTube-to-MP3 tool to download the audio, then enhance it in Hearably Studio with EQ + volume boost. Perfect for offline listening, DJ sets, or sharing on social media.
Three clicks to better audio
Install
Add Hearably from the Chrome Web Store. Under 300KB, installs in seconds.
Enhance
Click the Hearably icon and tap "Enhance." Boost kicks in instantly.
Enjoy
Adjust volume, EQ, and presets. Works on any website with audio.
Frequently asked questions
What does audio compression actually do?
Audio compression reduces the dynamic range of a signal — the difference between the loudest and quietest parts. It makes loud parts quieter relative to quiet parts, resulting in more consistent, even-sounding audio. This is essential for podcasts, music mastering, voiceovers, and any audio that will be played on devices with limited dynamic range like phones and laptops.
What is threshold and how do I set it correctly?
Threshold is the level (in dB) at which the compressor starts reducing gain. Audio below the threshold passes through unaffected; audio above it gets compressed according to the ratio. For speech, start at -20 dB. For music mastering, start at -15 dB. Listen for the moment the audio sounds "controlled" without sounding squashed.
What is the difference between ratio 2:1 and 8:1?
At 2:1, for every 2 dB the signal exceeds the threshold, only 1 dB comes through — gentle, transparent compression. At 8:1, for every 8 dB over threshold, only 1 dB passes — aggressive compression approaching limiting. Use 2:1 to 4:1 for music and general use. Use 6:1 to 10:1 for broadcast speech, heavy limiting, and aggressive dynamics control.
Why does Hearably use multiband compression instead of single-band?
Single-band compression applies the same gain reduction across all frequencies. A loud bass note triggers compression that also ducks the vocals and highs. Multiband compression splits the audio into frequency bands (250 Hz and 4 kHz in Hearably) and compresses each independently, so bass dynamics do not affect vocal clarity and vice versa.
Do I need Pro for the manual compressor controls?
The free tier includes the multiband compressor with automatic settings that scale with the volume boost level. Pro unlocks full manual control over threshold, ratio, attack, and release for each of the 3 bands, plus A/B preview and batch processing.
What is the difference between RMS and peak detection?
Peak detection reacts to individual sample values — the absolute highest point of the waveform. RMS detection measures the average energy over a short time window, which corresponds more closely to perceived loudness. RMS compression sounds smoother and more natural on complex material like music and speech. Hearably uses RMS detection.
Can I use compression to make a podcast louder?
Yes — compression plus makeup gain is exactly how broadcast audio achieves consistent loudness. Compress with a -20 dB threshold and 3:1 ratio to even out volume variations, then apply makeup gain to bring the overall level up. The look-ahead limiter prevents any clipping. This is the standard podcast mastering workflow.
Will compression make my audio sound bad?
Only if over-applied. Gentle compression (2:1 to 4:1 ratio, moderate threshold) is transparent and makes audio more pleasant to listen to. Heavy compression (8:1+, low threshold) can cause audible pumping and breathing artifacts. Use the A/B preview in Pro to compare your compressed audio against the original and find the right balance.