Converting Notes to Frequencies

Submitted on: 1/6/2015 3:18:00 PM
By: Lawilog (from psc cd)  
Level: Beginner
User Rating: By 9 Users
Compatibility: C, C++ (general), Microsoft Visual C++, Borland C++, UNIX C++
Views: 5661
     here i describe how can convert notes used in music (like c, d, e, f, g, a, b, c sharp, g flat,...) into frequencies you can use e.g. for the pc-speeker or whatever you like. if you think it's usefull, please vote!


Converting Notes to Frequencies

OK. To calculate any frequency, you need to know three things:

  • First: The fact, that a tone (note ?, i'm from germany...), that sounds one octave higher has a dobbeld frequency.
    So, if e.g. C has a frequency of 264 Hz, C one octave higher has 264 Hz * 2 = 528 Hz...still one octave higher it is 528 Hz * 2 = 1056 Hz - and so on.
  • Second, you need a start frequency of one special tone to create a function that calculates all the others.
    e.g. ("concert pitch") A = 440 Hz
  • And last but not least: in music it is said, that one octave has 12 halftones. (7 white and 5 black keys ;-)... )

Now, it is up to you, which halftone you suppose your concert pitch to be. On an normal (non-professional) piano keyboard concert pitch A would be the 58th one. which means, that there are still 4 lower octaves. (A is the 10th out of the 12, and 10 + 4*12 = 58)

...all these mathamitical and musical theorie, sorry...
Growing exponentially, the function has the following form: f(n) = k * a^n.
You know, the 58th halftone has a freq of 440. One octave higher, the 70th halftone (58+12=70) has a dobbeled freq of 880.
good. that means:
440 = k * a^58 and
880 = k * a^70
Now you transform both equqtions to "k = ...", set them equal, and calculate a with 2^(1/12). Now you use the caclulated a in one equation to get k with 440 * 2^(-58/12).
Now, you have your equation f = 440 * 2^(-58/12) * (2^(1/12))^n which is equal to:

f = 440 * 2^((n - 58)/12)

And that's it !

I will give you some examples:

note / tone n frequency in Hz
B (one octace below)48246.9
C sharp (D flat)50277.2
D sharp (E flat)52311.1
F sharp (G flat)55370.0
G sharp (A flat)57415.3
A sharp (B flat)59466.2
C (next octave)61523.3

So far, so good.
Now, it is up to you, to create a code, that can play meldoies. Maybe you would like to have a function first, that converts the note-string ("c", "g", "d flat", "g sharp",...) to a frequency. Than you may need a good way of storing the melodie-data (with note length and so on); a playing engine; even a midi-driver is possible... :D
But this is not what I am going to do for you. :D

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