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A .mid file writes each note as two events: a note-on where it starts, and a note-off where it ends. A scanner pairs them into one note, whose length is the number of ticks between them:
Here a green note is held from tick 1920 to tick 2400, and a second green note starts where it ends and is held to tick 2880. A red note at tick 2880 has no sustain. A .chart file writes each note’s length in the note itself. See Notes.

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Pairing

These rules apply to every note of an instrument track: notes, modifiers and phrases. Vocal tracks pair the same way, and trim overlapping notes of one pitch as sustains are trimmed: see Vocals and harmonies.
  • A note-off ends a note of its own number and channel.
  • A note-on with velocity 0 is a note-off. A note-off’s velocity has no effect.
  • Required: a note-off later in its track for every note-on.
  • Required: each note ends at or before the tick where the next note of its number and channel starts.
  • Recommended: every note of a track on one channel.

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Events at one tick

A note that ends where the next starts. Required: the note-off before the next note-on of its number, when the two share a tick. Then every scanner reads two notes, as in the example above. Edge case: a note of length 0. A note-on, then its note-off, at one tick. A note of length 0 has no sustain, and a modifier of length 0 covers the notes on its tick. For a phrase, see Phrases.

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Length

A note’s length is its note-off’s tick minus its note-on’s tick. What it means depends on the note:

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The sustain cutoff

A note whose sustain is no longer than the cutoff is read with no sustain. In a .mid file, the cutoff is the resolution divided by 3, rounded down, plus 1:
  • sustain_cutoff_threshold in song.ini, in ticks, replaces it. See Settings.
  • The cutoff applies to notes, not to phrases or vocal notes.
A .chart file has no cutoff by default. See Cut off short sustains. After pairing and the cutoff, a scanner resolves the notes as in a .chart file. See How notes resolve. It decides strums and HOPOs with the .mid rules on Note modifiers.

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Invalid forms

A scanner ends the latest open note of the number first, then trims overlapping sustains, as How notes resolve says. So two overlapping notes read as they would in a .chart file. Clone Hero, YARG and scan-chart read them this way. scan-chart reports overlappingMidiNotes. Saving with scan-chart keeps them as written.
Clone Hero, YARG and scan-chart keep the longer note, as in a .chart file. scan-chart’s export writes the longer one.
For notes that should end and start at one tick, the file has the next note-on before the note-off. Clone Hero, YARG and scan-chart pair that note-on with the note-off at its tick, and trimming overlapping sustains then gives the two notes the charter meant. scan-chart reports overlappingMidiNotes, and its export writes the note-off first.
Every scanner ignores it, and also a note whose note-off comes after the end of track. scan-chart’s export leaves it out. YARG’s lyrics read a vocal phrase without its note-off differently: see Vocals and harmonies.
Every scanner ignores it, except YARG’s lyrics for a vocal phrase: see Vocals and harmonies.
The note-off doesn’t end the note, so every scanner ignores the note.