Revision of keys-to-frequencies.js

1 file changed, 39 insertions

keys-to-frequencies.js(file created)

		@@ -0,0 +1,39 @@
1	+	////
2	+	/// Return a frequency based on piano key
3	+	/// @param {Number} key [49]
4	+	/// @return {Number} frequency
5	+	////
6	+	const getFrequencyFromKey = (key = 49) => {
7	+	return 2 ** ((key - 49) / 12) * 440;
8	+	};
9	+
10	+	////
11	+	/// Convert a string-based key to a number-based key
12	+	////
13	+	const convertKeyStringToNumber = (key = "C4") => {
14	+	let series = key.match(/\d/g)[0];
15	+	let notes = ["A", "A#Bb", "B", "C", "C#Db", "D", "D#Eb", "E", "F", "F#Gb", "G", "G#Ab"];
16	+	let note = key.replace(/\d/g, '');
17	+
18	+	return (note.match(/[AB]/) ? series : series - 1) * 12 + notes.indexOf(note) + 1;
19	+	};
20	+
21	+	////
22	+	/// Return an array of frequencies from a starting key, array of semitone
23	+	/// intervals, and number of keys to convert.
24	+	/// @param {Number} keyStart [41] Middle C
25	+	/// @param {Array} keyIntervals [[0]]
26	+	/// @param {Number} keyCount [1]
27	+	/// @return {Array} frequencies
28	+	////
29	+	const getFrequenciesFromKeys = (keyStart = 41, keyIntervals = [0], keyCount = 1) => {
30	+	let frequencies = [getFrequencyFromKey(keyStart)];
31	+	let keyInterval = 0;
32	+
33	+	for (let count = 1; count < keyCount; count++) {
34	+	keyInterval += Number.parseFloat(keyIntervals[count % keyIntervals.length]);
35	+	frequencies.push(getFrequencyFromKey(keyStart + keyInterval));
36	+	}
37	+
38	+	return frequencies;
39	+	};

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