Darwin's Cat
Free Online Audio Mastering Tool

Free Automatic Mastering Tool

Drag & drop WAV file here or click to select

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Free Online Mastering

Professional mastering in a minute — no registration, no limits.

Just upload your track, choose a music style and platform — the algorithm will analyze your audio and automatically select optimal settings. No knobs to turn, but if you want to — all parameters are open for fine-tuning.

What your DAW can’t do. Automatic loudness targeting for Spotify, Apple Music, YouTube Music, CD — or universal for all streaming platforms. Genre-aware settings, track loudness analysis, limiter with 8x oversampling, BPM-synced compressor — all out of the box.

Two steps to the result:

  1. Upload a WAV file — analysis starts automatically

  2. Hit Start — compare and download your finished master

How It Works

Step 1: Configure for your music

  • Platform — Streaming (Spotify, Apple Music), YouTube, or CD. Determines target loudness and format.

  • Style — Jazz, Hip-Hop, Electronic, Pop, Country, Rock, Metal. Affects compression, attack, and frequency balance.

  • Dynamics — from soft (Dynamic) to aggressive (Extreme). Controls sound density.

Step 2: Upload your track

Drag and drop a WAV file into the upload zone. The player appears instantly while analysis runs in parallel: loudness (LUFS), true peak, dynamic range (LRA), and loudest section analysis. Metrics and settings appear within seconds.

Step 3: Master and compare

Hit Start — processing begins with a detailed log of every step. Switch between original and result right in your browser. Happy? Download.

Step 4: Experiment

Change settings without re-uploading. Each run is a separate master with its own parameters. Compare versions, hear the difference, pick the best. All results are saved — download any of them.

Limiter

The limiter is the main mastering tool. It raises the overall track loudness to the target level and prevents peaks from exceeding the allowed ceiling.

Why is this needed?

Streaming platforms normalize loudness — they’ll turn up a quiet track and turn down a loud one. But if peaks are too high, distortion will appear during MP3/AAC conversion. The limiter solves both problems: makes the track loud enough and protects against clipping.

Iterative precision:

The limiter works iteratively — up to 8 attempts until it hits the target within ±0.2 dB. After each attempt, the actual LUFS is measured, and gain is corrected. This guarantees precise target hitting even with aggressive settings.

If the target is physically unreachable (too loud for the given material) — the algorithm detects this and stops, delivering the best possible result.

Parameters:

  • Target LUFS — target loudness. Calculated automatically: platform + style + dynamics.

  • True Peak — peak ceiling. -1.0 dB for streaming, -0.3 dB for CD. Safety margin ensures guaranteed non-exceedance.

  • Oversample — processing precision. 4x or 8x for reliable inter-sample peak control. Signal is upsampled to 192 kHz (at 4x), limited, then downsampled directly to the final sample rate — no intermediate step.

Compressor

The glue compressor binds the mix together, adds punch, and controls dynamics. It works gently — doesn’t kill the liveliness, but makes the sound tighter and more cohesive.

When is it needed?

For most modern genres — Rock, Pop, Electronic, Hip-Hop, Metal. For Jazz and classical music, you can disable it to preserve natural dynamics.

Smart threshold:

The threshold is calculated not from peaks (which are random), but from the loudest sections of the track — 95th percentile of short-term LUFS (3-second windows). This means the compressor responds to actual music — choruses, drops — not a random stick click or clap.

Parameters:

  • Ratio — compression amount. 1.5:1 — gentle glue, 4:1 — tight control. Calculated from Density + Dynamics.

  • Threshold — activation level in dB. Everything louder gets compressed. Calculated relative to the loudest sections of the track.

  • Attack — reaction speed. Fast (8–12 ms) for transient control, slow (30+ ms) to let drum clicks through. Metal and Electronic get fast attack, Jazz and Country get slow.

  • Release — recovery time. Calculated from BPM: 60000 / BPM / divisor. Faster tempo = shorter release. The compressor breathes in rhythm with the music.

  • Knee — softness of onset. Hard (1–2 dB) for punch and aggression, soft (6–8 dB) for transparent gluing. Metal gets hard knee, Jazz gets maximum softness.

  • Density — compression density: Light, Medium, Heavy. Determines base ratio, threshold offset, and attack.

Smart automation:

All parameters adapt to the combination of style, density, and dynamics. Metal + Heavy + Loud = fast attack, hard knee, aggressive ratio. Jazz + Light + Dynamic = slow attack, soft knee, minimal compression (or complete bypass). Everything can be overridden manually in Advanced mode.

Equalizer

Tonal correction for final polishing. The high-pass filter removes unwanted rumble, and five bands allow you to adjust the tonal balance.

HPF (High-Pass Filter)

Cuts sub-bass garbage below 15-50 Hz. The cutoff frequency is automatically selected based on genre and density: lower for Electronic and Hip-Hop (15 Hz — infrasound only), higher for Rock and Metal (30-35 Hz — removes rumble). Heavy Density adds +5 Hz, Loud Dynamics adds +6 Hz. Works before the compressor — so the compressor doesn’t react to sub-bass garbage.

Tonal bands:

Band Frequency Purpose When to use

Low End

80 Hz (shelf)

Adds weight and sub-bass

Mix sounds thin/empty, lacking foundation. Don’t use on already bassy mixes.

Warmth

150 Hz (bell, Q=0.7)

Body and fullness

Mix sounds cold/thin in the low-mids. Adds "meat" to guitars and vocals.

Mud

290 Hz (bell, Q=0.8)

Removes muddiness (cut only)

Mix sounds muddy/boxy. Common problem with home recordings. Cuts -1.5 or -3 dB.

Brightness

8 kHz (shelf)

Presence and clarity

Mix sounds dull, vocals get lost. Adds "sparkle" and intelligibility.

Air

12 kHz (shelf)

Air and openness of highs

Want a sense of space and "expensive" sound. Careful — may emphasize sibilance.

Each band has several fixed values — from off to +3 dB. Simple choice instead of endless knob turning.

Tip
 If you’re not sure you need EQ — don’t enable it. Mastering EQ should correct, not color. If the mix is well balanced, EQ isn’t needed.

Platforms and Formats

Each platform has its own loudness and peak level requirements. Select your target platform — the rest is calculated automatically.

Platform LUFS True Peak Sample Rate

Streaming

-14 dB

-1.0 dBTP

unchanged

YouTube

-14 dB

-1.0 dBTP

48 kHz

CD

-12 dB

-0.3 dBTP

44.1 kHz, 16 bit

Streaming — universal preset for all music streaming services:

  • Spotify

  • Apple Music

  • YouTube Music

  • Amazon Music

  • Tidal

  • Deezer

  • SoundCloud

Preserves your project’s original sample rate.

YouTube — for video content. Converts to 48 kHz, the video platform standard.

CD — classic 44.1 kHz / 16 bit format with dithering for quality bit depth reduction.

Tip
 If unsure — choose Streaming. This master will work for any platform.

Privacy

We’re musicians ourselves — we built this tool for ourselves and simply share it with you. Colleagues, after all ;)

Your files are safe:

  • Uploaded tracks are stored on the server for maximum 14 days

  • After that, they are automatically deleted without recovery

  • Not shared or used anywhere

  • Not indexed and not accessible via direct link

We don’t collect listening statistics, don’t analyze content, and don’t train neural networks on your tracks. Upload — process — download — forget.

About Us

Darwin’s Cat — that’s us, musicians from Berlin. We write rock, experiment with sound, and build tools we’re missing.

This mastering is a free gift to the music community. Enjoy!

Want to say thanks?

Feedback

Found a bug? Have an idea? Want a new feature? Write to admin@lafox.net — we read everything.