About directaudio.ch

directaudio.ch is a browser-based audio tempo adjuster for people who want their music to match a target pace—especially runners syncing playlists to their cadence. It detects BPM and retimes tracks to a chosen tempo without changing pitch, and it all happens locally in your browser using the Web Audio API, WebAssembly, and Web Workers.

Why it exists

Running feels better when your music lines up with your steps. This app helps you hit that sweet spot by suggesting tempos close to your cadence and avoiding extreme stretches. It even picks the nearest harmonic (with ¾, ½, and ¼ fallbacks plus sensible midpoints) so songs still sound natural.

How it works

• BPM detection runs in a web worker, keeping the interface snappy.
• High-quality time-stretching uses Rubber Band compiled to WebAssembly to preserve pitch while changing tempo.
• On-device exporting creates MP3s (via LAME.js) and WAV/µ-law WAV—no uploads required.

Privacy first

Your audio never leaves your device. There are no server APIs, no remote processing, and no long-term storage of your files.

Key features

• Drag & drop multiple tracks with per-file progress, cancel, and ZIP download.
• Smart target-tempo suggestions with optional midpoints to minimize artifacts (toggle in Settings).
• Works offline as a Progressive Web App; responsive UI with light/dark theme.
• Six languages (EN/DE/FR/IT/ES/PT).

Ready to try it? Drop in your tracks, pick a tempo, and go.