KTransposer

A simple chord and note transposer for kotlin applications.

It exposes an API named KTransposer that allows developers transpose single notes, chords, or even whole songs.

Samples:

Transpose a Single Note

val transposer = KTransposer()
val result = transposer.transposeNote(
    note = "G",
    semitones = -2
)

// Result: "A"

Transpose a Single Chord

val transposer = KTransposer()
val result = transposer.transposeChord(
    chord = "Dm7",
    semitones = 3
)

// Result: "Fm7"

Transpose a Whole Song

val autumnLeaves = """
    Bm             Em7
    The falling leaves
    A7             D7M
    Drift by my window
    G7M          C#m7(b5)
    The autumn leaves
    F#7           Bm
    Of red and gold
""".trimIndent()

val transposer = KTransposer()
val result = transposer.transposeSong(
    song = autumnLeaves,
    semitones = 4
)

// Result:
// """
//  D#m             G#m7
//  The falling leaves
//  C#7             F#7M
//  Drift by my window
//  B7M          Fm7(b5)
//  The autumn leaves
//  Bb7           D#m
//  Of red and gold
// """

Explicit Note Modifier

You can control if the result will show flat (b) or sharp (#) notes using the parameter preferredModifier.

val transposer = KTransposer()
val sharpResult = transposer.transposeNote(
    note = "C",
    semitones = 3, 
    preferredModifier = NoteModifier.SHARP 
)
val flatResult = transposer.transposeNote(
    note = "C",
    semitones = 3,
    preferredModifier = NoteModifier.FLAT
)

// Sharp Result: "D#"

// Flat Result: "Eb"

// * This logic can be applied to chords and songs too.

Custom Chord Regex

The default regex covers many of commonly used chord formats. You can check it here. But if you need any advanced chord format, you can create a custom regex and pass it to KTransposer constructor param chordPatternRegex.

val neverGonnaGiveYouUp = """
          Gb7Maj         Ab 
    Never gonna give you up
                F-      Bb-                        
    Never gonna let you down
          Gb7Maj    Ab         F-     Bb-      
    Never gonna run around and desert you
""".trimIndent()

val myCustomRegex: String = "... something you need ..."
val transposer = KTransposer(myCustomRegex)
val result = transposer.transposeSong(
    song = neverGonnaGiveYouUp,
    semitones = 1
)

// Result:
// """
//        G7Maj          A 
//  Never gonna give you up
//              F#-     B-                        
//  Never gonna let you down
//        G7Maj     A          F#-    B-      
//  Never gonna run around and desert you
// """

If you see any bugs or improvements in this library, please submit a new issue here.