Music function examples
The MUSIC package directory contains a collection of utility functions for converting between different musical measures. You can convert between frequencies, tones, and character notes. There are also functions for calculating the number of cents between two notes.
Contents
Scientific Pitch Notation
Scientific pitch notation is a character-based method of specifying a note. There are two parts: the note and the octave. For example, middle C on the piano 'C4' and the low E string on a guitar is 'E2'.
notes = {'C3', 'A3', 'A4', 'Bb6'}
notes =
'C3' 'A3' 'A4' 'Bb6'
Semitones
A semitone is equal to one half-step. For example, A# is one semitone above A. Semitones can also specify an absolute note. In this package, the term 'semitone' means the number of half-steps above or below C4. C4 is 'middle C' on a piano and is a common musical reference datum.
tones = music.note2tone(notes)
tones = -12 -3 9 34
Frequency
The frequency of a note doubles every octave. For example A3 is 220 Hz and A4 is 440 Hz.
freqs = music.note2freq(notes)
freqs =
130.81 220 440 1864.7
Musical Interval
The formats above are ways of specifying absolute pitches. In music theory however the most important characteristic of a note is its position in a key. C3 and C4 are different frequencies but they can be substituted for each other in a musical phrase. The passage will still sound correct and pleasing to the ear (assuming it was pleasing to begin with!).
In this representation we derive the interval of a note within a given key, as well as the absolute octave it occurs in.
[intervalsC,octavesC] = music.note2interval(notes,'C') % key of 'C' [intervalsG,octavesG] = music.note2interval(notes,'G') % key of 'G'
intervalsC =
0 9 9 10
octavesC =
3 3 4 6
intervalsG =
5 2 2 3
octavesG =
3 3 4 6
Centitones
A cent is a logarithmic measure of note spacing. A semitone is equal to 100 cents and there are 1200 cents in an octave. They are frequently used when tuning instruments as a measure of how close a pitch is to the correct frequency. For example, a guitar string can be considered tuned if it is within +/- 10 cents of the correct pitch.
cents = music.note2cent('C4',notes)
cents =
-1200 -300 900 3400