music.js

music-notes.html

<script>
   var convert = function () {
   	document.getElementById("result").innerHTML = 
   		"<font face=\"Geneva, Arial, Helvetica, sans-serif\">" +
   		frequencyToNote() + "</font>";
   }
   
   var frequencyToNote = function () {
   	var input = Number(document.getElementById("frequency").value);
   	if(isNaN(input) || (input == 0))
   		return "<font color=\"red\">Enter a numerical value for frequency</font>";
   	if((input < 27.5) || (input > 14080))
   		return "<font color=\"red\">Enter a frequency in the range 27.5Hz (A0) and 14080Hz (A9)</font>";
   	
   	var A4 = 440.0;
   	var A4_INDEX = 57;
   
   	var notes = [
   		"C0","C#0","D0","D#0","E0","F0","F#0","G0","G#0","A0","A#0","B0",
   		"C1","C#1","D1","D#1","E1","F1","F#1","G1","G#1","A1","A#1","B1",
   		"C2","C#2","D2","D#2","E2","F2","F#2","G2","G#2","A2","A#2","B2",
   		"C3","C#3","D3","D#3","E3","F3","F#3","G3","G#3","A3","A#3","B3",
   		"C4","C#4","D4","D#4","E4","F4","F#4","G4","G#4","A4","A#4","B4",
   		"C5","C#5","D5","D#5","E5","F5","F#5","G5","G#5","A5","A#5","B5",
   		"C6","C#6","D6","D#6","E6","F6","F#6","G6","G#6","A6","A#6","B6",
   		"C7","C#7","D7","D#7","E7","F7","F#7","G7","G#7","A7","A#7","B7",
   		"C8","C#8","D8","D#8","E8","F8","F#8","G8","G#8","A8","A#8","B8",
   		"C9","C#9","D9","D#9","E9","F9","F#9","G9","G#9","A9","A#9","B9" ];
   
   	var MINUS = 0;
   	var PLUS = 1;
   	
   	var frequency;
   	var r = Math.pow(2.0, 1.0/12.0);
   	var cent = Math.pow(2.0, 1.0/1200.0);
   	var r_index = 0;
   	var cent_index = 0;
   	var side;  
   
   	frequency = A4;
   
   	if(input >= frequency) {
   		while(input >= r*frequency) {
   			frequency = r*frequency;
   			r_index++;
   		}
   		while(input > cent*frequency) {
   			frequency = cent*frequency;
   			cent_index++;
   		}
   		if((cent*frequency - input) < (input - frequency))
   			cent_index++;
   		if(cent_index > 50) {
   			r_index++;
   			cent_index = 100 - cent_index;
   			if(cent_index != 0)
   				side = MINUS;
   			else
   				side = PLUS;
   		}
   		else
   			side = PLUS;
   	}
   
   	else {
   		while(input <= frequency/r) {
   			frequency = frequency/r;
   			r_index--;
   		}
   		while(input < frequency/cent) {
   			frequency = frequency/cent;
   			cent_index++;
   		}
   		if((input - frequency/cent) < (frequency - input))
   			cent_index++;
   		if(cent_index >= 50) {
   			r_index--;
   			cent_index = 100 - cent_index;
   			side = PLUS;
   		}
   		else {
   			if(cent_index != 0)
   				side = MINUS;
   			else
   				side = PLUS;
   		}  
   	}
   
   	var result = notes[A4_INDEX + r_index];
   	if(side == PLUS)
   		result = result + " plus ";
   	else
   		result = result + " minus ";
   	result = result + cent_index + " cents";
   	return result;
   }
</script>