Siren incorporates Francois Pachet's MusES pitch class package. A pitch class is an abstraction of a single pitch or note name (e.g., C in any octave, or 'fa' in any key), and there are relationships for pitch class spelling (f#, la flat), pitch equivalence, enharmonic equivalence (do sharp = re flat), and interval algebra.

Based on this, chords and scales can be defined according to pitch class rules.

To make the code easy to use, MusES puts a shortcut in the Smalltalk global dictionary; the global variable N holds the PitchClass class, making the following code examples easier to read.

Print these to see results, or look at the advanced EventGenerator examples.

Pitch expressions (print these)
   [N C sharp sharp]
   [N C augmentedFourth]
   [N C diminishedThirteenth]
   [N C augmentedFourth pitchEqual: N C diminishedFifth]
   [N D sharp closestEnharmonic]
   [N E flat closestEnharmonic]

Intervals
   [N do flat intervalBetween: N sol]
   [MusicalInterval perfectFourth topIfBottomIs: N F sharp]
   [MusicalInterval allIntervalsType: 4]

Scales
   [PitchClass B majorScale notes]
   [PitchClass D flat melodicMinorScale notes]

To use a scale as real pitches, you need to give it an octave, as in
   [PitchClass C majorScale asPitchesInOctave: 5]
   [(HungarianMinor root: N fa) asPitchesInOctave: 2]

Chords
   (PitchClassChord new fromString: 'C') notes
   (PitchClassChord new fromString: 'Re maj7') notes
   (PitchClassChord new fromString: 'C 13 aug9') notes
   (PitchClassChord new fromString: 'C aug9 dim5') notes

Key signatures
   [Signature choseSignature]
   [(Signature new nbSharps: 4) tonality]
   [Signature fromTonality: N E flat majorScale]

EventList Examples using Scales

   [((NeapolitanMinor root: N do) generateChordsPoly: 5 inOctave: 3) scrambled] p

Extending the Models of Pitch Classes and Scales

Obviously, this framework is designed for ease of extension, and new interval types, scale rules, families of key signatures are all straightforward to add.