note-to-frequency/src/index.js

🎼 converts a note (scientific pitch notation) to a frequency

// @flow

import validateNote from 'validate-note';

import getPosition from './lib/getPosition';

type options = {
  base: number,
  maxOctave: number
};

export default (note: string, {base = 440, maxOctave = 8}: options = {}): number => {

  const {letter, octave, signature} = validateNote(note, {
    flatToSharp: true,
    maxOctave,
    octave: true
  });

  const pos: number = getPosition(letter, octave, signature);
  const basePos: number = getPosition(`A`, 4);
  const diff: number = pos - basePos;

  const a: number = 2 ** (1 / 12);
  return Math.round((base * (a ** diff)) * 100) / 100;

};