converts a note (as a string) to a frequency in hertz

note2hertz.cpp

#include "note.h"
#include <math.h>
#include <algorithm>

// note string structure:
// [A-G][0-9][f,n,s]
// A-G: Note entre La (A) et Sol (G)
// 0-9: Octave du piano
// f: bémol (flat), n: naturel, s: dièse (sharp)
// Donc "D3s" va jour le troisième Ré dièse du piano


// list of notes and list of their corresponding frequencies
string note_names[] = {
  "A",  "A#", "B",  "C",
  "C#", "D",  "D#", "E",
  "F",  "F#", "G",  "G#"
};

float note_hertz[] = {
  440.0,  466.16, 493.88, 523.25,
  554.37, 587.33, 622.25, 659.25,
  698.46, 739.99, 783.99, 830.61
};

float Note::getHertz(){
  // calculate the frequency of the note in hertz
  // based on the note string.
  // The tuning is A4 = 440 Hz, equal temperament
  // get the note modifier (sharp, flat, natural)
  char modifier = note[note.length()-1];
  int offset;
  switch (modifier) {
    case 's': offset = 1; break;
    case 'f': offset = -1; break;
    case 'n': offset = 0; break;
    default: offset = 0;
  }
  // get the octave value
  int octave = note[note.length()-2] - '0';
  octave -= 4;
  // Get the first character of the note string
  string note_name = note.substr(0, 1);
  // Find the note in the note_names array and adjust the offset
  int index = find(note_names, note_names + 12, note_name) - note_names + offset;
  // if the note index is below 0, lower the octave by 1 and add 12 to the index
  // if the note index is above 11, raise the octave by 1 and subtract 12 from the index
  switch (index) {
    case -1: octave--; index = 11; break;
    case 12: octave++; index = 0; break;
  };
  // calculate the frequency of the note
  // based on the note index and the octave
  float hertz = note_hertz[index] * pow(2, octave);
}