How the Improvisation Trainer checks your playing

In the Improvisation Trainer, the template shows where you can play, but you choose what to play. Here’s how GrooveDojo checks your notes.

A subdivision template gives each beat a subdivision, such as 8ths, triplets or 16ths, and each one gives the beat a few places where a note can go. Play any drum, or several together, on any of them. You never have to play every place. Rests are allowed but don’t affect your score.

When you practice a composition instead, its notes are checked for timing on any drum, as a groove’s are (how drum timing works).

One beat, split three ways. Each dot is a place where a note fits.

Does it fit?

GrooveDojo measures each note from the click, as it does in a groove, and finds the nearest place of its beat’s subdivision. It shows where the note landed. It can’t know which rhythm you meant.

Every note gets one of three results:

Fits: it landed on or near one of its beat’s places.
Doesn’t fit: it landed clearly closer to a place another subdivision would use, such as a triplet note in a beat of 8ths.
Not checked: GrooveDojo couldn’t reliably check the note, for example during a quick roll or grace note.

A note that doesn’t fit isn’t wrong music. It’s outside this exercise.

Was it early or late?

Only a note that fits gets a timing. It’s measured against the click, using your Timing mark window (±30 ms unless you change it in Settings, Practice). The window changes how the timing is shown, never whether a note fits.

Which place? The &: it fits.
How early or late? 40 ms early.

A note can fit its place and still be early.

Notes between two places

A note within 30 ms of one of its beat’s places always fits. Further off, a note between a place of its beat and a place of another subdivision counts for its beat, early or late, unless it’s clearly closer to the other place: more than two thirds of the way there.

Three notes after the & at 80 BPM, each measured from the click: 20 ms late is on time, 60 ms late fits and is late, and 105 ms late landed closer to the triplets’ let, so it doesn’t fit.

Your score

The session review shows the percentage of checked beats that fit. A beat fits when every note in it fits the selected subdivision.

If a note doesn’t fit, its whole beat doesn’t fit. Here, 8 of 10 checked beats fit, giving you 80%.

Beats with notes that couldn’t be checked are left out of the score, not counted as wrong. Rests and beats when your kit was disconnected are also excluded.

Loop by loop shows how each beat went on every pass. How this was counted gives you the full breakdown.

Where to focus breaks down your results by subdivision, shows where notes most often didn’t fit, and highlights the subdivision changes that gave you the most trouble. Practice next suggests a built-in template and tempo to work on.

The review also highlights consistent early or late playing when there’s enough evidence. More detail shows your usual timing, while Rhythms you played summarizes the rhythms you used. None of this is a score for creativity.

Limits

Close subdivisions are hard to tell apart. In templates that mix triplets and 16ths, some places are only 50 ms apart at 100 BPM, and closer at faster tempos. A note between them counts for its beat unless it’s clearly closer to the other place, so a note played in the other rhythm can still fit, and a note you meant can land closer to the other place. Practice’s setup tells you when places are this close at your tempo.
Your setup adds delay. MIDI, your computer and your headphones all take a little time. A small, consistent delay can shift your timing readings. A delay that varies from hit to hit can make it harder to tell where your notes land, and Bluetooth audio is too slow and unsteady to rely on (how drum timing works).
Some playing isn’t checked: grace notes, rolls, and the hi-hat foot unless you choose to check it.
Straight feel only, in time signatures such as 3/4 and 4/4.

What has been tested?

I’ve tested the Improvisation Trainer with my Roland TD-27KV2 in Chrome on a Mac. Automated tests also cover subdivision matching, scoring, live feedback and session review.

The trainer hasn’t been tested on every kit or browser, and I haven’t measured its accuracy across different setups. Results can be affected by your kit, computer and audio setup, and some notes can’t be checked reliably.

How drum timing works: how each hit from your kit is timed, and the delays GrooveDojo can’t correct for.
Questions about timing feedback

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