Stackable Metronome

A browser polymetric groove trainer / metronome — and the design mockup for a Raspberry Pi Pico hardware build. Stack as many "meter lanes" as you like; each is its own little metronome with a grouping, subdivision, drum voice and per-beat pattern. Layering lanes produces polymeter and true ratio polyrhythm.

Live: https://metronome.varasys.io

It's a single page (index.html) plus a vendored QR library — no build step, no framework. State (presets, set lists, practice log, theme) lives in localStorage.

Features

• Meter lanes — grouping (odd meters), subdivision, GM drum voice, per‑beat on/off pattern (rests), mute, live measure counter.
• Polyrhythm — a per‑lane poly toggle fits a lane's beats evenly into lane 1's bar (e.g. 5‑over‑4, 3‑over‑2).
• Practice — gap/mute trainer (play N / mute M bars) and a tempo ramp with a start BPM and signed step.
• Set lists — named, ordered lists of saved setups; ▶ loads + starts an item, N advances; each play is logged for cross‑day comparison.
• Sharing — copy a link (with QR) to your current settings or a whole set list.
• Theming — System / Light / Dark.

The share language

A compact, human‑readable text encodes a full configuration (a patch). It's what goes in a share link, and you can hand‑write or edit it.

Patch grammar

v1 ; t<bpm> [; vol<pct>] ; <lane> ; <lane> … [; tr<play>/<mute>] [; rmp<start>/<step>/<every>]

Token	Meaning	Example
v1	format version (always first)	v1
t<bpm>	tempo	t120
vol<pct>	master volume 0–100	vol70
tr<play>/<mute>	gap trainer: play N bars, mute M	tr2/2
rmp<start>/<step>/<every>	tempo ramp: start BPM, ±step, every N bars	rmp80/5/4
<lane>	a meter lane (see below)	kick:4

Tokens are joined with ;. tr and rmp are omitted when off.

Lane grammar

<sound> : <grouping> [ / <sub> ] [ = <pattern> ] [ ~ ] [ ! ]

• sound — one of: beep, kick, snare, rim, clap, hatClosed, hatOpen, ride, crash, tomLow, tomMid, tomHigh, tambourine, cowbell, woodblock, claves, jamblock (unknown → beep).
• grouping — beats per bar, optionally grouped for odd meters: 4, 3, 2+2+3. The first beat of each group is accented.
• /sub — subdivision (clicks per beat): 1 quarter (default), 2 eighth, 3 triplet, 4 sixteenth, 6 sextuplet. Omit for quarter.
• =pattern — per‑beat on/off as x/., length = beats per bar. Omit = all on. e.g. =.x.x puts a backbeat on 2 & 4.
• ~ — polyrhythm: fit this lane's beats evenly into lane 1's bar.
• ! — mute the lane.

Examples

Patch / lane	What it is
kick:4	kick on 4 quarter beats
snare:4=.x.x	snare backbeat (2 & 4)
hatClosed:4/2	eighth‑note hi‑hats
claves:5~	5 evenly across lane 1's bar (5‑over‑4 if lane 1 is 4)
kick:2+2+3=x..x..x	7/8, kick on each group start
cowbell:3+2/2	5/4 grouped 3+2, eighth subdivision
Full: v1;t120;kick:4;snare:4=.x.x;hatClosed:4/2;tr2/2	backbeat groove with gap trainer

In URLs

• Settings: …/#p=<patch> — readable, e.g. …/#p=v1;t120;kick:4;claves:5~
• Set list: …/#sl=<base64url> — a JSON {title, description, items[]} where each item's config is a patch string. Used because titles/notes are free text.

Opening such a link applies the settings (or imports the set list) on load, then clears the hash so a refresh won't re‑import.

Sharing

In the set‑list panel's ⋯ menu:

• Share settings link / Share set‑list link open a dialog with the link to Copy or Open.
• QR ↗ opens a third‑party QR service (api.qrserver.com) with the link in its URL so you can scan it on a phone. A banner warns you it's external — confirm the QR decodes to the shown link before trusting it. (No QR is generated locally.)
• Export all / Import file back up presets + set lists + logs as a JSON file.

Keyboard shortcuts

Key	Action
P	play / stop
T	tap tempo
↑ / ↓	tempo ±1 (Shift = ±10)
A	add meter lane
1–9	mute lane N
R	toggle the set‑list panel
N	next set‑list item
?	shortcuts help
Esc	close dialog / panel

Versioning

VERSION holds the formal version. deploy.sh stamps the served page:

• Formal — a clean commit tagged v<VERSION> → X.Y.Z.
• Dev — anything else → X.Y.Z-dev.<utc-timestamp>.<short-sha>[.dirty].

Cut a release with ./release.sh [X.Y.Z] (bumps VERSION + tags v<VERSION>), then push the tag and deploy.

Deploy

./deploy.sh copies index.html (version‑stamped) into the Caddy web root and smoke‑tests the live URL. No restart needed (file_server picks up changes immediately).

Files

File	Purpose
index.html	the whole app
deploy.sh	publish to the Caddy web root
release.sh	tag a formal version
VERSION	formal version string