music-spelling

* Music spelling
A Common Lisp library for automatically spelling pitches and rhythms.

Pitch spelling uses an algorithm appropriate for non-tonal contexts. It attempts to:
- avoid unnecessary accidentals;
- avoid diminished and augmented intervals between consecutive notes;
- avoid spellings such as E♯, F♭, B♯, C♭;
- avoid ascending with flats or descending with sharps.

Each of these situations carries a penalty value, which can be configured.

Rhythm spelling takes care of ties and dots, constraining durations to meter, and following the best practices for sustained notes across beats (as found in Gould, E. (2011). /Behind bars: The definitive guide to music notation/. Faber Music.).

* Install
#+begin_src lisp
(ql:quickload "music-spelling")
#+end_src

* Usage
** Pitches
~pitch-spell~ takes a list of midi note numbers and returns a list of ~note~ objects.

For example:
#+begin_src lisp
(pitch-spell '(48 50 52 53 55 57 59 60 61 64 65 68 69))

--> (#<NOTE C3> #<NOTE D3> #<NOTE E3> #<NOTE F3> #<NOTE G3> #<NOTE A3> #<NOTE B3>
 #<NOTE C4> #<NOTE C#4> #<NOTE E4> #<NOTE F4> #<NOTE Ab4> #<NOTE A4>)
#+end_src

Penalties for unwanted cases are configured by default in the hash table ~*default-penalties*~ with the following contents:
#+begin_src
:ACCIDENTALS = 1.0 
:AUGMENTED = 1.4 
:DIMINISHED = 1.5 
:DIRECTION = 1.6 
:DOUBLE-ACCIDENTALS = 2.5 
:|E#-FB-B#-CB| = 0.4 
:OTHER-INTERVALS = 8.0 
:PARSIMONY = 1.2 
#+end_src
These reflect my preferences, but this is much a matter of personal choice.

Different preferences can also be followed:
#+begin_src lisp
(pitch-spell '(60 63 66 69 73 74) :penalties (make-penalties :double-accidentals 1.2))

--> (#<NOTE C4> #<NOTE Eb4> #<NOTE Gb4> #<NOTE Bbb4> #<NOTE Db5> #<NOTE D5>)
#+end_src
Which relaxed the avoidance of double-flats (from 2.5 to 1.2). Compare to the default:
#+begin_src lisp
(pitch-spell '(60 63 66 69 73 74))

--> (#<NOTE C4> #<NOTE Eb4> #<NOTE F#4> #<NOTE A4> #<NOTE C#5> #<NOTE D5>)
#+end_src

/Parsimony/ is the spelling of a note that changes a previously used accidental. For example, G♭ following a G♯. It can also be used to declare a preference for some specific note spellings, or enforce them strictly by simultaneously ramping up the ~:parsimony~ penalty. Like in the following example:
#+begin_src lisp
(pitch-spell '(60 61 63 67 68 70)
	     :parsimony (make-parsimony '(#\d . :flat)
					'(#\g . :sharp)
					'(#\a . :natural)
					'(#\b . :flat))
	     :penalties (make-penalties :parsimony 10))

--> (#<NOTE C4> #<NOTE Db4> #<NOTE Eb4> #<NOTE Fx4> #<NOTE G#4> #<NOTE Bb4>)
#+end_src

For chords, use ~pitch-spell-chords~:
#+begin_src lisp
(pitch-spell-chords '((60 64 67) (61 65 68) (62 66 69)))

--> ((#<NOTE C4> #<NOTE E4> #<NOTE G4>) (#<NOTE Db4> #<NOTE F4> #<NOTE Ab4>)
 (#<NOTE D4> #<NOTE F#4> #<NOTE A4>))
#+end_src
Chords follow a different set of rules, expressed by default in ~*chord-penalties*~.

** Rhythms
~rhythm-spell~ takes a list of pitches (midi notes, ~note~ objects, or other representation) and a list of durations, expressed as fractions or multiples of one beat, returning a list with notes, durations as reciprocals of the beat length, and dots (~:dot~ after the affected note) and ties (~:tie~ between tied notes) where appropriate. The format is convenient e.g. for exporting to Lilypond format.

For example:
#+begin_src lisp
(rhythm-spell (pitch-spell '(60 62 65 66 68)) '(1.5 1.75 0.5 2 .25))

--> (#<NOTE C4> 4 :DOT #<NOTE D4> 8 :TIE #<NOTE D4> 4 :TIE #<NOTE D4> 16 #<NOTE F4>
 8 #<NOTE F#4> 16 :TIE #<NOTE F#4> 4 :DOT :DOT #<NOTE G#4> 16)
#+end_src

* Current limitations
** Pitches
- algorithm doesn't provide an automatic segmentation across different phrases
** Rhythms
- no tuplets
- no compound time
- meters other than 4/4 probably produce incorrect results

* License
Apache 2.0

* Author
[[https://nunotrocado.com][Nuno Trocado]]


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