A Dart package for transposing chords into any given key.

Features

• Transpose chords from one key to another
• Transpose chords up or down semitones
• Find chords in lyrics and transpose them into another key
• Find chords in lyrics and transpose up or down semitones
• Support for different notation systems (English, German, and German with accidentals)
• Case sensitivity support (preserves lowercase/uppercase chord format)

Usage

First initialize the ChordTransposer:

final transposer = ChordTransposer();

Notation systems

The package supports three different notation systems:

// English notation (default)
final transposer = ChordTransposer();
// or explicitly
final englishTransposer = ChordTransposer(notation: NoteNotation.english);

// German notation
final germanTransposer = ChordTransposer(notation: NoteNotation.german);

// German notation with accidentals
final germanAccTransposer = ChordTransposer(notation: NoteNotation.germanWithAccidentals);

Notation comparison

English	German	German with Accidentals
C	C	C
C#	Cis	C#
Db	Des	Db
D	D	D
D#	Dis	D#
Eb	Es	Eb
E	E	E
F	F	F
F#	Fis	F#
Gb	Ges	Gb
G	G	G
G#	Gis	G#
Ab	As	Ab
A	A	A
A#	Ais	A#
Bb	B	B
B	H	H

Transpose chords

Transpose a single chord from one key to another:

// English notation
transposer.chordToKey(chord: 'D/F#', fromKey: 'A', toKey: 'G'); // => C/E

// German notation
germanTransposer.chordToKey(chord: 'D/Fis', fromKey: 'A', toKey: 'G'); // => C/E

Transpose multiple chords from one key to another. If fromKey is not given, it will use the first chord in the list:

// English notation
transposer.chordsToKey(chords: ['C', 'F', 'Am', 'G7', 'Bdim'], toKey: 'E'); // => [E, A, C#m, B7, D#dim]

// German notation
germanTransposer.chordsToKey(chords: ['C', 'F', 'Am', 'G7', 'Hdim'], toKey: 'E'); // => [E, A, C#m, B7, Disdim]

Transpose a single chord up or down semitones:

// English notation
transposer.chordUp(chord: 'D', semitones: 5); // => G
transposer.chordDown(chord: 'Bb', semitones: 2); // => Ab

// German notation
germanTransposer.chordUp(chord: 'D', semitones: 5); // => G
germanTransposer.chordDown(chord: 'B', semitones: 2); // => As

Transpose multiple chords up or down semitones:

// English notation
transposer.chordsUp(chords: ['D','Aadd9'], semitones: 4); // => [Gb, Dbadd9]
transposer.chordsDown(chords: ['Bb7/D', 'Eb'], semitones: 6); // => [E7/G#, A]

// German notation
germanTransposer.chordsUp(chords: ['D','Aadd9'], semitones: 4); // => [Ges, Desadd9]
germanTransposer.chordsDown(chords: ['B7/D', 'Es'], semitones: 6); // => [E7/Gis, A]

Transpose lyrics

final lyrics = '''
[C]Twinkle, twinkle [F]little [C]star.
[F]How I [C]wonder [G7]what you [C]are.
''';

Tranpose lyrics from one key to another. If fromKey is not given, it will use the first chord in the lyrics. When ignoreInvalids is set to true (default), it will ignore all invalid chords. When it is set to false, it will throw an error if there is an invalid chord:

transposer.lyricsToKey(lyrics: lyrics, fromKey: 'C', toKey: 'G'); // =>
// [G]Twinkle, twinkle [C]little [G]star.
// [C]How I [G]wonder [D7]what you [G]are.

Transpose lyrics up or down semitones:

// English notation
transposer.lyricsUp(lyrics: lyrics, semitones: 5); // =>
// [F]Twinkle, twinkle [A#]little [F]star.
// [A#]How I [F]wonder [C7]what you [F]are.

// German notation
germanTransposer.lyricsUp(lyrics: lyrics, semitones: 5); // =>
// [F]Twinkle, twinkle [B]little [F]star.
// [B]How I [F]wonder [C7]what you [F]are.

// English notation
transposer.lyricsDown(lyrics: lyrics, semitones: 3); // =>
// [A]Twinkle, twinkle [D]little [A]star.
// [D]How I [A]wonder [E7]what you [A]are.

// German notation
germanTransposer.lyricsDown(lyrics: lyrics, semitones: 3); // =>
// [A]Twinkle, twinkle [D]little [A]star.
// [D]How I [A]wonder [E7]what you [A]are.

Additional information

This package built to work with paurakhsharma's flutter_chord package and was inpsired by ddycai's chord-transposer npm package.