RACK4MASTER / Auto

Spectral Auto Mastering Processor
Intelligent EQ, dynamics and stereo correction that runs entirely in your browser. No uploads, no accounts, no tracking.

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✨ Features

• Spectral Reference Matching — auto-matches your track's tonal balance using FFT + Meyda ISO 1/3-octave analysis
• 7-Band Parametric EQ — sub, bass, lo-mid, mid, hi-mid, presence and air bands (±12 dB)
• Dynamics Processor — compressor with threshold, ratio, attack, release and makeup gain
• HPF + Saturation — high-pass filter with resonance control and harmonic saturation
• M/S Output Stage — independent mid/side gain, limiter ceiling and output gain
• A/B Comparison — seamless real-time toggle between original and mastered signal (12 ms crossfade, no position reset)
• Live DSP Chain — real-time preview of the processed signal before export; loop button on both original and output players
• Spectral Comparison View — overlaid spectrum on both input and output canvases
• WAV Export — 16-bit PCM offline render with 0.5 s compressor pre-roll for clean transients
• Preset system — save / load processing chains as JSON files
• Internationalisation — English · Español · Català via hamburger menu (always starts in English)
• Donate button — PayPal link in the footer
• 100% browser — Web Audio API, zero server-side processing, zero data collection

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📸 Screenshots

Main application window with track loaded.

Analysis panel showing auto-correction decisions.

Live DSP chain, A/B button, loop controls and WAV export.

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🚀 Getting Started

No build step or install required. Just open index.html in a modern browser (Chrome / Edge / Firefox / Safari 16+).

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📁 File Structure

rack4master-auto/
├── index.html    — Markup only; data-i18n attributes for live translation
├── style.css     — All styles (rack UI, hamburger menu, A/B button, responsive)
├── script.js     — DSP engine, Web Audio graph, UI logic, transport, A/B, export
├── i18n.js       — Translations (EN / ES / CA) + t() / setLang() / initI18n()
├── help.html     — Help page (linked from hamburger menu)
└── README.md     — This file

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🎛 A/B Comparison

The A/B button in the output transport row toggles between:

State	Colour	Signal
B · MASTERED	Green	Full DSP chain (EQ + comp + M/S + limiter)
A · ORIGINAL	Amber	Dry bypass — same source, no processing

Switching is click-free: a 12 ms gain ramp crossfades between a dryGain node (parallel bypass) and the fadeGain at the end of the wet chain. Playback position never resets.

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🔁 Loop Controls

Both the input and output players have independent loop buttons. The output loop wraps the BufferSource natively (src.loop = true) and the RAF progress display uses modulo so the waveform and seek bar animate correctly through each cycle.

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🌐 Internationalisation

Translations live in i18n.js inside the TRANSLATIONS object. All three languages (EN / ES / CA) cover the same 71 keys. To add a new language:

1. Add a new key block (e.g. fr: { ... }) mirroring the en block.
2. Add <button class="lang-btn" data-lang="fr">FR</button> inside .ham-lang in index.html.

Static elements use data-i18n="key" (updated by setLang()). Dynamic strings — status bar, prompts, report table — call t('key') directly in JS.

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🛠 Technical Notes

• DSP chain: HPF → 7-band peaking EQ → waveshaper (saturation) → compressor → M/S matrix → limiter → output gain → analyser → fadeGain
• Bypass path: BufferSource also connects to dryGain → destination in parallel; A/B cross-fades between fadeGain and dryGain
• FFT: custom Cooley–Tukey for spectrum display; Meyda for perceptual analysis
• Export: OfflineAudioContext with 0.5 s pre-roll silence to warm the compressor envelope, then trimmed before WAV encoding
• No frameworks — vanilla JS, zero dependencies beyond Meyda CDN