Drums

The drums app trains rhythm patterns — short loops of one or two measures on a percussion staff — and whole grooves as real drummers played them, built for the Yamaha FGDP-50 finger-drum pad (any GM-style pad controller works).

How it differs from piano

• No hand selection, no calibration — pads are pads.
• Pads map to notation: drum notation encodes each instrument as a pitch and notehead shape (bass drum, snare, hi-hat, toms, cymbal). Incoming pad hits are matched back to the notated instrument through the pad map (below), and alternate pads for the same instrument (rimshot → snare, open → closed hi-hat) count as hits, in rhythm and practice mode alike.
• Patterns loop: at the end of a pattern of up to four bars, playback wraps around with a short lead-in — keep grooving. Anything longer, a groove or a whole chart, plays through once and stops, and its score scrolls under the cursor as the saxophone’s does.

How it sounds

Pads play a drum kit, not a piano: twelve voices covering kick, snare, rim, closed and open hi-hat, ride and crash, three toms, clap, cowbell and tambourine. They respond to how hard you hit, a closed hi-hat chokes the open one the way the pedal does, and alternate pads for the same instrument make the same sound.

The kit is synthesized rather than sampled, so there is nothing to download and it works offline — including in the desktop app, where sampled instruments need the network on first use.

Your kit’s pad map

Every drum module sends its own MIDI notes. General MIDI fixes the common ones: 38 for the snare, 42 for the closed hi-hat, and so on. Many modules add their own, such as edge zones, rims and extra toms, and many let you re-assign any pad. The 🥁 button in the header opens the pad map: every kit voice, with the notes that play it.

• It starts as General MIDI, alternates included, so a GM kit works with no setup.
• Teach it your kit: press Learn on a voice and hit every pad or zone that should play it. Hit a hi-hat’s bow and its edge, and both count as the hi-hat. You can also type a note number.
• Test as you go: the panel shows the note each hit sends and what it plays, and the kit sounds through the new map straight away. A note that is not assigned makes no sound and scores nothing.
• Each note plays one voice, so learning it for another voice moves it. The × on a note unassigns it, and Reset to General MIDI starts over.

The map is saved on this device. The header button is highlighted while a custom map is in use. Clap, cowbell and tambourine score like the rest of the kit now; before the map, those three pads were missing from the scoring table.

The step-sequencer grid

Below the staff, the music is also shown as a grid: one row per instrument, one column per subdivision (16 columns for sixteenth feels, 12 for triplet/12-8 feels), with the playhead sweeping column by column. Same music, two notations — read the staff, verify with the grid.

The grid never moves. As the playhead leaves a column, the column turns to the same step of the next bar: ahead of the cursor is the rest of this bar, behind it — faintly shaded — the start of the next. A pattern reads round and round, and a long groove reads as it goes, a beat ahead of your hands.

Pads work best on the desktop app

The desktop app reads your pad controller through the operating system’s own MIDI stack, so it is picked up the moment you plug it in, hot-plugging included. Nothing else changes.

Pattern generator

The song picker’s 🎛 Pattern generator entry writes patterns for you. Drums have no scales, so what you choose is a kit and a density: a 16-step sequencer where you pick the voices and how many times each should hit in the bar.

Set the numbers by hand, or hit 🎲 Propose to roll playable ones for the kit you assembled. Every cell stays editable — click any square to add or remove a hit, and the counter follows.

The algorithms

Pure randomness sounds like noise, because rhythm needs metric hierarchy and anchor points. Each engine below answers the same question — given this many hits, which of the 16 steps?

Algorithm	What it does
Euclidean (Bjorklund)	spreads the hits as evenly as possible — the distribution behind most world ostinatos. E(5,8) is the Cuban cinquillo, E(4,16) is four-on-the-floor, E(8,16) straight eighths
Metric-weighted Bernoulli	samples against the hierarchy of the bar: downbeat, backbeats, half-bar, eighth offbeats, then sixteenth ghost notes
Shift register	the Turing-machine trick: a locked loop that starts mutating as you raise the variation
Markov chain	each step conditioned on the one before, with a separate matrix per step so it never loses the downbeat
Cellular automata	Wolfram rules 30, 90 and 110 over the 16 cells, advancing one generation per bar — patterns that evolve instead of looping

Each voice bends the hierarchy toward its own job, so a Euclidean snare lands on 2 and 4 while the kick keeps the downbeat.

Variation and dynamics

• Variation between bars decides how much later bars drift: at 0% the pattern is an exact loop, and a few percent drops or nudges the odd hit, the way a drummer varies a groove. The automata evolve instead.
• Accents and velocity come from 1/f pink noise, so dynamics group across a phrase rather than flickering from hit to hit.

Patterns are engraved as real percussion notation — two layers, kick stems down, beamed per beat, accents marked — and play like any other piece, with the step grid reading them back:

Every pattern has a seed, so the exercise you started is the one you come back to, and its stats accumulate like any other piece.

Grooves

The song picker’s 🥁 Grooves entry is real drummers’ playing, to read and play along with: the 1,150 performances of Magenta’s Groove MIDI Dataset — ten drummers on an electronic kit, playing to a click, in 18 styles from rock and funk to jazz, Afro-Cuban and Brazilian: grooves of up to twenty minutes, and fills of a bar or two.

A performance is not a score: every hit is a few milliseconds off the click, a drummer sits a little ahead of it or behind, a shuffle’s eighths are somewhere between straight and triplets. So each one is put on a grid the way a drummer would write it down — the drummer’s own time taken out, then each beat on the simplest grid that holds its hits, and the groove’s feel kept from beat to beat, so a shuffle stays in triplets and a funk groove in sixteenths. Ghost notes come out in brackets and accents are marked; the ride is on the top line and the hi-hat foot below the staff, as on a drummer’s chart.

• Find one by style, tempo, length, feel (straight or swung) or drummer — beats, fills or both.
• Choose the grid: as played, or all straight, or all triplets.
• A long take comes in parts of 32 bars, or whole up to 128 bars.
• Preview it, ▶ Listen to its first bars — ghost notes soft, accents loud — and start it.

A groove plays through and stops at the end, the score scrolling under the cursor; drag the page to move through it, or set a loop range to work on a passage. A fill loops like a pattern.

The dataset is Magenta’s (Google), released under the CC BY 4.0 licence; the scores are the app’s reading of the performances.