Chords

The chords module computes chord notes and diatonic chord relationships across 22 chord types:

• Triads: major-triad, minor-triad, diminished-triad, augmented-triad
• 7th chords: major-7th, minor-7th, dominant-7th, diminished-7th, half-diminished-7th
• 6th chords: major-6th, minor-6th
• Suspended chords: sus2, sus4
• 9th chords: major-9th, minor-9th, dominant-9th
• 11th chords: major-11th, minor-11th, dominant-11th
• 13th chords: major-13th, minor-13th, dominant-13th

getChordNotes(root, chordType) returns the notes of any chord type built on a root.

getDiatonicChords(root, mode) returns the 7 diatonic triads for a key/mode, one per scale degree, in degree order (defaults to Ionian/major). getChordByDegree(degree, root, mode) returns just the chord at one degree (1-7).

getAvailableInversions(chordType) returns every valid value for a chord type’s inversion parameter - 0 is root position, not itself an inversion. A triad allows 0-2 (root position plus 2 inversions); a 13th chord allows 0-6 (root position plus 6 inversions).

getChordInversion(chord, inversion) reorders a chord’s notes so the given inversion’s tone is lowest, throwing a RangeError if it’s out of range for that chord’s type.

detectChords(notes) identifies every chord (root, type) match for a set of notes, keyed by root - the reverse of getChordNotes. Exact match only; returns {} if nothing matches.

Multiple valid roots are common: symmetric chords (augmented-triad, diminished-7th), minor-7th/major-6th overlap, and the whole 13th-chord family all produce more than one entry.

Live Playground

getChordNotes

getChordNotes(root: Note, chordType: ChordType): Note[]

Returns the notes of a chord type built on a root.

ResultC, E, G

getDiatonicChords

getDiatonicChords(root: Note, mode?: ModeName): Chord[]

Returns the 7 diatonic triads for a key/mode, one per scale degree.

Result

[
  {
    "root": "C",
    "type": "major-triad"
  },
  {
    "root": "D",
    "type": "minor-triad"
  },
  {
    "root": "E",
    "type": "minor-triad"
  },
  {
    "root": "F",
    "type": "major-triad"
  },
  {
    "root": "G",
    "type": "major-triad"
  },
  {
    "root": "A",
    "type": "minor-triad"
  },
  {
    "root": "B",
    "type": "diminished-triad"
  }
]

getChordByDegree

getChordByDegree(degree: number, root: Note, mode?: ModeName): Chord

Returns the diatonic chord at a specific scale degree (1-7).

Result

{
  "root": "C",
  "type": "major-triad"
}

getAvailableInversions

getAvailableInversions(chordType: ChordType): readonly ChordInversion[]

Returns the valid inversion numbers for a chord type, based on its note count.

Result[0, 1, 2]

getChordInversion

getChordInversion(chord: Chord, inversion: ChordInversion): Note[]

Reorders a chord's notes so the given inversion's chord tone is lowest.

ResultC, E, G

detectChords

detectChords(notes: Note[]): Partial<Record<Note, ChordType[]>>

Returns every chord that matches a set of notes, as key-value pairs mapping each matching root note to its list of matching chord types. Pick an example to see how a note set can match more than one root.

Input notesC, E, G

Result

{
  "C": [
    "major-triad"
  ]
}