Intelligent EQ Auto-mastering — 100% in-browser
Rack4Master mini is a web-based auto-mastering application that runs entirely in your browser, requiring no external servers or installations. It analyzes the spectrum and dynamics of any audio file, suggests intelligent corrections, and applies a professional processing chain in real-time, delivering exportable high-quality WAV results.
If you find RACK4MASTER-MINI useful, help us grow by giving a star on GitHub:
You can also donate via PayPal to keep improving the tool.
Supports drag-and-drop or file selection for MP3, WAV, OGG, FLAC, and AAC formats.
Interactive visual player with waveform rendering based on WaveSurfer.js v6. The playhead is clickable and draggable for easy track navigation.
- Play / Pause / Stop with keyboard shortcuts (
Space,S). - Real-time display of current time and total duration.
- Adjustable Loop Region: Draggable S (Start) and E (End) handles on the waveform to define specific repeat zones.
The audio engine implements a wet/dry chain with click-free crossfading:
| Stage | Description |
|---|---|
| Low Shelf EQ | Bass boost or cut (150 Hz). |
| High Shelf EQ | Treble boost or cut (5 kHz). |
| Mid Peak EQ | Vocal range control (1.5 kHz). |
| Harsh Peak EQ | Presence and sibilance control (3.5 kHz). |
| Compressor | DynamicsCompressor with ratio, threshold, attack, release, and makeup gain. |
| Saturation | WaveShaper with a configurable soft-clip curve. |
| Stereo Width | Independent M/S control for the side channel. |
| Limiter | High-ratio compressor at -0.5 dB, fully configurable. |
The ON/OFF button provides a full bypass with smooth crossfading between the dry and processed signals.
Analyzes the decoded buffer using a proprietary FFT (Cooley-Tukey radix-2) and generates a report with up to 8 automatic diagnostics:
- Excessive or lacking highs (spectral brightness).
- Excessive or lacking lows (60–150 Hz energy ratio).
- Harshness in the 2–5 kHz range (listening fatigue).
- Recessed or dominant mids (vocal range 500–3000 Hz).
- Excessive or normal dynamic range (suggests appropriate compression).
- Aggressive transients (crest factor).
- Lack of harmonic warmth (suggests saturation).
- Stereo field issues (too narrow or excessively wide).
Each diagnostic includes an on/off toggle and a fine-tuning slider to adjust the suggested parameters in real-time while listening.
General Neutral · Soft Mastering · Broadcast
Genres Rock · Pop · Jazz · Blues · Ballad · Folk · Country · Urban/Hip-Hop · Latin
Style Warm Vintage · Bright & Open · Punchy · Lo-Fi
Each preset features a thumbnail showing EQ bars and compression points. Once selected, it applies instantly and opens a fine-tuning panel with sliders for relevant parameters (neutral parameters are hidden). Compression is exposed via a single Intensity slider that interpolates between neutral and target values.
- WAV: Offline rendering via
OfflineAudioContextusing the same processing chain, exported as a 16-bit PCM stereo WAV. - Preset JSON: Save and load your full parameter configurations in JSON format to reuse across different sessions.
| Key | Action |
|---|---|
Space |
Play / Pause |
S |
Stop |
L |
Loop on/off |
B |
Bypass on/off |
- A modern browser with Web Audio API and OfflineAudioContext support.
- A local web server (XAMPP, Live Server, etc.) to avoid CORS restrictions.
- No Node.js, bundlers, or npm dependencies required.
🎚️ Need more control? If you are looking for granular adjustments and a professional mastering rack, check out the full version: rack4master.
If you find RACK4MASTER-MINI useful, you can support the project with a donation:
Rack4Master mini — professional audio processing, right in your browser.