Note by Note 作者： Note by Note

Note by Note turns any audio or video in your browser into a practice tool.

It opens in the sidebar and processes the page's audio in real time, so you can drop a song into your instrument's key, slow a solo to half speed without the chipmunk effect, and loop four bars until they stick. YouTube lessons, backing tracks, streamed albums, or an mp3 on your own disk — if it plays in the browser, you can practise along with it.

Pitch and speed

• Transpose ±12 semitones, or ±36 with extended range turned on. Speed is untouched.
• Fine-tune in cents, or pin playback to a reference pitch if you're playing with a group tuned to 415 Hz instead of 440.
• Speed runs from 25% to 200% and leaves pitch exactly where it is.
• Pitch shifting and time stretching come from the Rubber Band Library's realtime R3 engine, compiled to a WebAssembly AudioWorklet — the same algorithm used by desktop audio software.

Practice structure

• Drop markers on the timeline as you listen, and set a loop range between any two points.
• Click a marker tile to loop its section; drag across tiles, or shift-click a second one, to loop everything in between.
• Add a count-in so you're not scrambling on the downbeat of every repeat.
• Save any loop as a snippet, then chain snippets into a sequence: play the solo four times at 50%, then three times at 75%, then twice at full speed — without touching the panel between passes.

Sound

• A vocal reducer (STFT centre-cut, written for this project) pushes the centre-panned voice down so the band comes forward — or inverts it to isolate the vocal instead.
• A 10-band EQ with saveable presets, plus built-in curves that lean the mix toward guitar, bass, drums or vocals.

Chords

• Optional chord and key detection runs a machine-learning model over the audio, entirely on your machine, and draws a chart under the timeline.

Keeping your place

• Markers, loops, snippets and effect settings are saved per track against the page URL, so reopening a video brings your practice setup back with it.
• Favourites and recently practised tracks live in a library tab.
• Optional cross-device sync copies that setup to your other browsers.

How it connects

Nothing is requested when you install it. The first time you press Connect, the extension asks for site access once, rather than interrupting you on every new site. Settings → Revoke Permissions takes it back at any time.

Most pages attach directly: a Web Audio graph on the page's own audio or video element, with the full feature set. This is the YouTube path. A few pages block that — DRM-protected streams, cross-origin media, or a strict content-security policy — and the panel says so instead of half-working. Settings → Play local file opens a player for files on your disk, where nothing is restricted.

Privacy

• No telemetry. No analytics. No ads. No accounts. Nothing is sold or shared.
• Audio never leaves your device. Every effect — pitch, speed, vocal reduction, EQ, chord detection — runs locally in your browser.
• Cross-device sync is the only network request the extension ever makes. It is on by default and can be switched off in Settings, and it carries no audio: just your settings, markers, loops, snippets, and the page URLs and titles of the tracks in your library.
• Full policy: PRIVACY.md

Open source

Note by Note is free software under the GPL-2.0-or-later. The complete source, including the audio engine, is at github.com/patrickiel/note-by-note — bug reports and contributions welcome.

Requires Firefox 140 or later. The sidebar is desktop-only, so Firefox for Android is not supported.