Project

Rhythm Checker

Your phone hears every hit and tells you, in milliseconds, whether you rushed or dragged. Its tuner checks each drum.

Open the app Source

Rhythm Checker’s rudiment drill on a phone: the single paradiddle at 120 beats per minute, its sticking with the accents marked, the notes scrolling toward the hit line, and a meter from early to late for each hit

40drum rudiments to drill

1 msto the millisecond, on every hit

84tests with planted timing errors

$0cloud cost to run it

In motion

The rudiment highway: each hit comes back early or late.

Calibration: here the microphone lags 8 milliseconds.

Timing: hold 120 beats per minute for 30 seconds and see which way you drift.

Tuner: the needle shows how far off its target each head rings.

History: ten weeks of sessions at a glance, ready to export.

Rhythm Checker, liveOpen in a new tab

Open the live app

It asks for the microphone only when you start a drill, and everything stays on your device.

Why I built it

Behind the kit, a fill feels locked in. On the recording, it rushed by a hair. I play drums in a band, so I built Rhythm Checker to tell me which one is true.

It deliberately doesn’t judge the groove: sometimes dragging behind the beat is the whole point of a song.

What I decided

Practice in rudiments, as drummers already do: each one a drill with its own target.
Do all the signal processing on the device. No cloud, no running cost.
Calibrate the microphone’s lag once per phone. Otherwise the app would read the lag as your timing, and you’d spend a week fixing a problem you don’t have.
Keep the deep analysis out of the app. A Python tool digs in afterward: drift over a whole take and history across weeks.

Try it

Open the app on an iPhone in Safari and add it to your home screen. After the first visit it works offline.