HERTZ

High-fidelity client-side audio processing engine.

HERTZ is a web-based Digital Audio Workstation (DAW) utility designed for instant vocal polishing. It leverages the Web Audio API for real-time signal processing and FFmpeg.wasm for client-side encoding. Unlike traditional tools that rely on server-side processing (FFmpeg binaries on Linux), HERTZ runs entirely within the user's browser thread via WebAssembly.

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Core Architecture

The application is built on a "Zero-Server" architecture. The goal is to eliminate the latency, bandwidth costs, and privacy risks associated with uploading sensitive audio data to cloud storage.

The Pipeline

1. Ingestion: Decodes varied input formats (WAV, MP3, M4A, OGG) into a raw 32-bit floating-point AudioBuffer.
2. Manipulation: Provides a non-destructive editing layer using Wavesurfer.js regions, allowing users to define sample-accurate start/end points.
3. Digital Signal Processing (DSP):
   • Constructs an OfflineAudioContext for faster-than-realtime rendering.
   • Routes audio through a hardcoded vocal chain (EQ -> Compressor -> Limiter).
   • Analysis pass determines peak amplitude for accurate normalization.
4. Encoding:
   • Transfers processed buffer to the ffmpeg.wasm virtual file system.
   • Executes LAME MP3 encoding at 192kbps VBR.
   • Streams the resulting Blob directly to the user's download manager.

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Signal Chain Specification

HERTZ does not use generic presets. The audio engine implements a specific vocal chain optimized for spoken word and podcast clarity.

1. High-Pass Filter

• Cutoff: 80Hz
• Q: 1.4
• Purpose: Removes sub-bass rumble and DC offset artifacts often present in consumer microphones.

2. Dynamics Compressor

A hard-knee compressor designed to level vocal dynamic range without introducing pumping artifacts.

• Threshold: -20.0 dB
• Ratio: 3.1:1
• Knee: 5.0 dB
• Attack: 0.03s (30ms)
• Release: 0.1s (100ms)

3. Normalization

Post-compression gain staging ensures compliance with broadcast loudness standards.

• Target: -3.0 dB Peak
• Method: Linear gain calculation based on absolute max amplitude scanning.

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Technical Constraints & Browser Security

HERTZ relies on SharedArrayBuffer to facilitate multi-threaded processing in FFmpeg.wasm. Modern browsers restrict this feature behind strict security headers to prevent Spectre/Meltdown vulnerabilities.

To run HERTZ locally or in production, the host must serve the following headers:

Cross-Origin-Opener-Policy: same-origin
Cross-Origin-Embedder-Policy: require-corp

If these headers are missing, ffmpeg.wasm will fail to initialize, and the application will throw a buffer allocation error. The included vite.config.ts handles this for local development.

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Installation & Development

Requirements

• Node.js 18.x or higher
• NPM or Bun package manager
• A modern browser with WebAssembly support (Chrome 90+, Firefox 90+, Safari 15+)

Setup

# Clone the repository
git clone [https://github.com/askpext/hertz.git](https://github.com/askpext/hertz.git)

# Enter directory
cd hertz

# Install dependencies
npm install

Running Locally

npm run dev

The application will launch at http://localhost:5173.

Building for Production

npm run build

This generates a static asset bundle in /dist. Note that you cannot simply open index.html locally; it must be served via a web server that supports the required COOP/COEP headers (e.g., Vercel, Netlify, or GitHub Pages).

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