chrisburnell / keys-to-frequencies.js

//// /// Return a frequency based on piano key /// @param {Number} key [49] /// @return {Number} frequency //// const getFrequencyFromKey = (key = 49) => { return 2 ** ((key - 49) / 12) * 440; }; //// /// Convert a string-based key to a number-based key //// const convertKeyStringToNumber = (key = "C4") => { let series = key.match(/\d/g)[0]; let notes = ["A", "A#Bb", "B", "C", "C#Db", "D", "D#Eb", "E", "F", "F#Gb", "G", "G#Ab"]; let note = key.replace(/\d/g, ''); return (note.match(/[AB]/) ? series : series - 1) * 12 + notes.indexOf(note) + 1; }; //// /// Return an array of frequencies from a starting key, array of semitone /// intervals, and number of keys to convert. /// @param {Number} keyStart [41] Middle C /// @param {Array} keyIntervals [[0]] /// @param {Number} keyCount [1] /// @return {Array} frequencies //// const getFrequenciesFromKeys = (keyStart = 41, keyIntervals = [0], keyCount = 1) => { let frequencies = [getFrequencyFromKey(keyStart)]; let keyInterval = 0; for (let count = 1; count < keyCount; count++) { keyInterval += Number.parseFloat(keyIntervals[count % keyIntervals.length]); frequencies.push(getFrequencyFromKey(keyStart + keyInterval)); } return frequencies; };