Swing Key Trainer

Tap the rhythm along with the click — any key, on each beat and each “and.” On a phone or any touchscreen, tap anywhere in the timeline or the distribution panel instead; both double as tap pads, since neither holds any controls. Each tap is read as whichever target it lands closer to, and the beat / and pills up top show how it was read, so you can catch the classifier disagreeing with you. The “and” taps are what get scored, against the gold line. One limit worth knowing: as the swing target climbs past about 85% the two targets sit close enough together that a late beat tap and an early “and” tap become genuinely hard to tell apart.

Beneath the timeline, on the right: on-beat −11 ms ± 18 ms. The mean, δ, is how far your beat taps sit from the click — negative means early — and the spread is how steady your pulse is. Neither touches the swing number, which comes only from your “and” taps against the click, so a wandering pulse shows up here instead of muddying the swing reading. It's still worth a glance, for two reasons. If δ is consistent — say reliably 30 ms early — your “and” taps are almost certainly shifted by the same amount, which quietly tilts the swing number by that share of a beat (30 ms at 90 bpm is about 4.5 points). And if the spread is wide, no single swing reading means much, however confident it looks.

A word on latency: the app lines your taps up against when the click actually reaches the speakers, not when it was scheduled, so it accounts for output latency as far as it can measure it — but that measurement isn't perfect on every machine, and nothing can see the delay between your ear, your hand, and the key. So treat δ above as the reality check. If your beat taps sit consistently early or late, that's either your natural feel or lag the app didn't fully catch; either way it's shown, never silently corrected, so what you read is what you did. The ± pp next to the swing figure is just the slack from your input's timing noise, given as a share of the beat, so it grows at faster tempos.

Reading the number: 50% is dead even, ~66.7% a triplet feel, 75% a dotted-eighth shuffle. Start gives you a one-bar count-in, then the headline averages your off-beats over the last 10 seconds — so it tracks recent playing, empties if you pause, and freezes where it was once you press Stop.