vail

music.mjs

 1/**
 2 * @file Musical notes and frequencies
 3 */
 4
 5/** One half step in equal temperament */
 6const semitone = Math.pow(2, 1/12)
 7const ln_semitone = Math.log(semitone)
 8const A4_note = 69
 9const A4_freq = 440
10const Cn1_note = 0
11const Cn1_freq = A4_freq / Math.pow(semitone, A4_note)
12
13const note_names = [
14    "C",
15    "C♯",
16    "D",
17    "E♭",
18    "E",
19    "F",
20    "F♯",
21    "G",
22    "A♭",
23    "A",
24    "B♭",
25    "B",
26]
27
28/**
29 * Convert a MIDI note to a frequency
30 * 
31 * @param {Number} note MIDI note number
32 * @returns {Number} Frequency (Hz)
33 */
34function MIDINoteFrequency(note, precision=0) {
35    let freq = Cn1_freq * Math.pow(semitone, note)
36    return freq.toFixed(precision)
37}
38
39/**
40 * Return closest matching MIDI note to a frequency
41 * 
42 * @param {Number} frequency Frequency (Hz)
43 * @returns {Number} Closest MIDI note
44 */
45function FrequencyMIDINote(frequency) {
46    return Math.round(Math.log(frequency/Cn1_freq) / ln_semitone)
47}
48
49function MIDINoteName(note) {
50    let octave = Math.floor(note / 12) - 1
51    return note_names[note % 12] + octave   
52}
53
54export {
55    MIDINoteFrequency,
56    FrequencyMIDINote,
57    MIDINoteName,
58}