#region License
/* Copyright (c) 2006 Leslie Sanford
*
* Permission is hereby granted, free of charge, to any person obtaining a copy
* of this software and associated documentation files (the "Software"), to
* deal in the Software without restriction, including without limitation the
* rights to use, copy, modify, merge, publish, distribute, sublicense, and/or
* sell copies of the Software, and to permit persons to whom the Software is
* furnished to do so, subject to the following conditions:
*
* The above copyright notice and this permission notice shall be included in
* all copies or substantial portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
* THE SOFTWARE.
*/
#endregion
#region Contact
/*
* Leslie Sanford
* Email: jabberdabber@hotmail.com
*/
#endregion
using System;
namespace Sanford.Multimedia.Midi
{
/// <summary>
/// Converts a MIDI note number to its corresponding frequency.
/// </summary>
public sealed class MidiNoteConverter
{
/// <summary>
/// The minimum value a note ID can have.
/// </summary>
public const int NoteIDMinValue = 0;
/// <summary>
/// The maximum value a note ID can have.
/// </summary>
public const int NoteIDMaxValue = 127;
// Table for holding frequency values.
private readonly static double[] NoteToFrequencyTable = new double[NoteIDMaxValue + 1];
static MidiNoteConverter()
{
// The number of notes per octave.
int notesPerOctave = 12;
// Reference frequency used for calculations.
double referenceFrequency = 440;
// The note ID of the reference frequency.
int referenceNoteID = 69;
double exponent;
// Fill table with the frequencies of all MIDI notes.
for(int i = 0; i < NoteToFrequencyTable.Length; i++)
{
exponent = (double)(i - referenceNoteID) / notesPerOctave;
NoteToFrequencyTable[i] = referenceFrequency * Math.Pow(2.0, exponent);
}
}
// Prevents instances of this class from being created - no need for
// an instance to be created since this class only has static methods.
private MidiNoteConverter()
{
}
/// <summary>
/// Converts the specified note to a frequency.
/// </summary>
/// <param name="noteID">
/// The ID of the note to convert.
/// </param>
/// <returns>
/// The frequency of the specified note.
/// </returns>
public static double NoteToFrequency(int noteID)
{
#region Require
if(noteID < NoteIDMinValue || noteID > NoteIDMaxValue)
{
throw new ArgumentOutOfRangeException("Note ID out of range.");
}
#endregion
return NoteToFrequencyTable[noteID];
}
/// <summary>
/// Converts the specified frequency to a note.
/// </summary>
/// <param name="frequency">
/// The frequency to convert.
/// </param>
/// <returns>
/// The ID of the note closest to the specified frequency.
/// </returns>
public static int FrequencyToNote(double frequency)
{
int noteID = 0;
bool found = false;
// Search for the note with a frequency near the specified frequency.
for(int i = 0; i < NoteIDMaxValue && !found; i++)
{
noteID = i;
// If the specified frequency is less than the frequency of
// the next note.
if(frequency < NoteToFrequency(noteID + 1))
{
// Indicate that the note ID for the specified frequency
// has been found.
found = true;
}
}
// If the note is not the first or last note, narrow the results.
if(noteID > 0 && noteID < NoteIDMaxValue)
{
// Get the frequency of the previous note.
double previousFrequncy = NoteToFrequency(noteID - 1);
// Get the frequency of the next note.
double nextFrequency = NoteToFrequency(noteID + 1);
// If the next note is closer in frequency than the previous note.
if(nextFrequency - frequency < frequency - previousFrequncy)
{
// Move to the next note.
noteID++;
}
}
return noteID;
}
}
}