A Swift function that converts a note (eg. "A4") to a frequency (eg. 440.0)

noteToFrequency.swift

// MIT License
// Swift that converts a string note (eg. "A4") to a frequency (eg. 440.0).
// Inspired by https://gist.github.com/stuartmemo/3766449
static func noteToFrequency (note: String) -> Double {
    let notes = ["A", "A#", "B", "C", "C#", "D", "D#", "E", "F", "F#", "G", "G#"]
    let octave = Double(String(note.last!))!
    var keyNumber = Double(notes.firstIndex(of: String(note.dropLast()))!)

    if (keyNumber < 3) {
        keyNumber += octave * 12 + 1
    } else {
        keyNumber += (octave - 1) * 12 + 1
    }

    return 440 * pow(2, (keyNumber - 49) / 12)
}