Octave and Semitones

Octave is the fundamental distance between the tones. The tones that are distant from one another for one octave are actually frequency doubles. Their waves are contained one within the other, or, we can say that they are two notes sound similar. In other words, if one tone has frequency x, the first upper octave tone will have frequency 2x and the first lower octave tone will have frequency x/2.

Semitones

Semitones are the steps within an octave. The Western tonal music system uses 12 semitones: A, A#, B, C, C#, D, D#, E, F, F#, G, G#. A semitone, also called a half step or a half tone, is the smallest musical interval used in the Western system. Each step is the same distance apart. The distance is measured as a ratio of frequencies, the next semitone has a frequency 2^(1/12) = 1.059 times the previous one.


Frequencies of the notes:

A = 440 Hz
A# = 466 Hz
B = 494 Hz
C = 523 Hz
C# = 554 Hz
D = 587 Hz
D# = 622 Hz
E = 659 Hz
F = 698 Hz
F# = 740 Hz
G = 784 Hz
G# = 831 Hz
A2 = 880 Hz