mirror of https://github.com/nealey/vail.git
58 lines
1.1 KiB
JavaScript
58 lines
1.1 KiB
JavaScript
/**
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* @file Musical notes and frequencies
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*/
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/** One half step in equal temperament */
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const semitone = Math.pow(2, 1/12)
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const ln_semitone = Math.log(semitone)
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const A4_note = 69
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const A4_freq = 440
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const Cn1_note = 0
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const Cn1_freq = A4_freq / Math.pow(semitone, A4_note)
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const note_names = [
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"C",
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"C♯",
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"D",
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"E♭",
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"E",
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"F",
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"F♯",
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"G",
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"A♭",
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"A",
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"B♭",
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"B",
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]
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/**
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* Convert a MIDI note to a frequency
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*
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* @param {Number} note MIDI note number
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* @returns {Number} Frequency (Hz)
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*/
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function MIDINoteFrequency(note, precision=0) {
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let freq = Cn1_freq * Math.pow(semitone, note)
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return freq.toFixed(precision)
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}
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/**
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* Return closest matching MIDI note to a frequency
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*
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* @param {Number} frequency Frequency (Hz)
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* @returns {Number} Closest MIDI note
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*/
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function FrequencyMIDINote(frequency) {
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return Math.round(Math.log(frequency/Cn1_freq) / ln_semitone)
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}
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function MIDINoteName(note) {
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let octave = Math.floor(note / 12) - 1
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return note_names[note % 12] + octave
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}
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export {
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MIDINoteFrequency,
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FrequencyMIDINote,
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MIDINoteName,
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} |