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Count-in and metronome

Ship the click a bandmate would give you. Before the song starts, the count-in taps out one bar so the reader locks into the tempo; during playback, the metronome keeps clicking on every beat. Both are staples of any practice tool worth shipping.

00:00 / 00:00
Playback state: Stopped

Hit play with the count-in enabled and the state readout flips to Count-in bar for one bar before advancing to Playing. The Restart from top button stops and re-plays without waiting for the song to end, so the lead-in fires again.

The two toggles​

alphaTab treats both clicks as monitoring channels rather than settings — flip them on by raising their volume above zero.

  • api.metronomeVolume — the click that runs during playback. 0 mutes it (the default). 1 matches the master output; typical values sit between 0.3 and 0.8.
  • api.countInVolume — the one-bar lead-in before the transport actually starts. Also defaults to 0. When non-zero, alphaTab inserts a count of the loaded bar's time signature before playback begins, then hands off to the score.

Both are floats in the [0, 1] range and can change at runtime. Wire them to a practice-mode toggle, a beginner switch, or a slider in your UI.

Detecting the count-in​

While the count-in is playing, playerPositionChanged reports a negative currentTick. The score's tick 0 is the first note of bar 1, so the count-in bar runs from a negative tick up to 0. A UI can hide the playback cursor or show a "Count-in" badge during that window:

api.playerPositionChanged.on((args) => {
  const isCountIn = args.currentTick < 0;
  document.body.classList.toggle('is-count-in', isCountIn);
});

playerStateChanged still fires with state = Playing for the count-in; the negative-tick check is what distinguishes the lead-in from the song itself.

Pick-up bars (new in 1.9)​

A pick-up bar (anacrusis) is shorter than its time signature, for example \ac in alphaTex or an implicit measure in MusicXML. alphaTab treats it as the end of a full bar and aligns beaming and playback to the real beats of the meter.

00:00 / 00:00
Playback state: Stopped
\ts (2 4)
\ac C4.8 D4.8 E4.8 |
F4.4 G4.4 |
A4.8 B4.8 C5.8 D5.8 |
C4.2

The pick-up holds the last three eighths of a 2/4 bar: C sits on the off-beat of beat 1, D and E on beat 2.

  • Metronome: clicks fall on the beats of the time signature inside the pick-up. The first click sounds with D, not with the first note.
  • Beaming and triplet feel: groups follow the same beat grid. C keeps its own flag, D and E are beamed together as beat 2. Triplet feel pairs the eighths on that grid too.
  • Count-in: counts one full bar and continues until the beat playback starts on. Here you hear 1, 2, 1, C enters on the off-beat that follows, and D falls on beat 2. The same applies when you start playback in the middle of a bar.

Show it in code​

import * as alphaTab from '@coderline/alphatab';

const container = getAlphaTabContainer();
const api = new alphaTab.AlphaTabApi(container, {
  core: { file: '/scores/song.gp' },
  player: {
    playerMode: alphaTab.PlayerMode.EnabledSynthesizer,
  },
});

// Enable the metronome at half volume during playback.
api.metronomeVolume = 0.5;

// Give the reader a one-bar count-in before the track starts.
api.countInVolume = 0.7;

api.playPause();

getAlphaTabContainer() is a placeholder for the platform-specific step of obtaining the render target — a <div> on Web, an AlphaTab control on .NET, or an AlphaTabView on Android. Every other line runs unchanged on all three runtimes.

Reacting to each click​

Every metronome tick fires through midiEventsPlayed as an AlphaTabMetronomeEvent. Subscribe if you want a visual flash, a haptic pulse on mobile, or a beat counter overlay. See The MIDI event stream for the subscription pattern.

Where to look next​