# MIDI note/frequency conversion¶

notes
```I get often asked about simple things like MIDI note/frequency conversion, so I thought I
The following is Pascal/Delphi syntax, but it shouldn't be a problem to convert it to
almost any language in no time.

Uses for this code are mainly for initializing oscillators to the right frequency based
upon a given MIDI note, but you might also check what MIDI note is closest to a given
frequency for pitch detection etc.
In realtime applications it might be a good idea to get rid of the power and log2
calculations and generate a lookup table on initialization.

A full Pascal/Delphi unit with these functions (including lookup table generation) and a
http://tobybear.phreque.com/dsp_conv.zip

```
code
 ``` 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53``` ```// MIDI NOTE/FREQUENCY CONVERSIONS const notes:array[0..11] of string= ('C ','C#','D ','D#','E ','F ','F#','G ','G#','A ','A#','B '); const base_a4=440; // set A4=440Hz // converts from MIDI note number to frequency // example: NoteToFrequency(12)=32.703 function NoteToFrequency(n:integer):double; begin if (n>=0)and(n<=119) then result:=base_a4*power(2,(n-57)/12) else result:=-1; end; // converts from MIDI note number to string // example: NoteToName(12)='C 1' function NoteToName(n:integer):string; begin if (n>=0)and(n<=119) then result:=notes[n mod 12]+inttostr(n div 12) else result:='---'; end; // converts from frequency to closest MIDI note // example: FrequencyToNote(443)=57 (A 4) function FrequencyToNote(f:double):integer; begin result:=round(12*log2(f/base_a4))+57; end; // converts from string to MIDI note // example: NameToNote('A4')=57 function NameToNote(s:string):integer; var c,i:integer; begin if length(s)=2 then s:=s+' '+s; if length(s)<>3 then begin result:=-1;exit end; s:=uppercase(s); c:=-1; for i:=0 to 11 do if notes[i]=copy(s,1,2) then begin c:=i; break end; try i:=strtoint(s); result:=i*12+c; except result:=-1; end; if c<0 then result:=-1; end; ```

```For the sake of completeness, here is octave fraction notation and pitch class notation:

// converts from MIDI note to octave fraction notation
// the integer part of the result is the octave number, where
// 8 is the octave starting with middle C. The fractional part
// is the note within the octave, where 1/12 represents a semitone.
// example: NoteToOct(57)=7.75
function NoteToOct(i:integer):double;
begin
result:=3+(i div 12)+(i mod 12)/12;
end;

// converts from MIDI note to pitch class notation
// the integer part of the number is the octave number, where
// 8 is the octave starting with middle C. The
fractional part
// is the note within the octave, where a 0.01 increment is a
// semitone.
// example: NoteToPch(57)=7.09
function NoteToPch(i:integer):double;
begin
result:=3+(i div 12)+(i mod 12)*0.01;
end;
```
```I thought most sources gave A-440Hz = MIDI note 69. MIDI 60 = middle C = ~262Hz, A-440 = "A above middle C". Not so?
```
• Date: 2003-05-14 03:24:58
• By: DFL
```Kaleja is correct. Here is some C code:

double MIDItoFreq( char keynum ) {
return 440.0 * pow( 2.0, ((double)keynum - 69.0) / 12.0 );
}

you can double-check the table here:
http://tomscarff.tripod.com/midi_analyser/midi_note_frequency.htm
```