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A jump from the lowest semitone to the highest semitone in one octave doubles the frequency (for example, the fifth A is 440 Hz and the sixth A is 880 Hz). The frequency of a pitch is derived by multiplying (ascending) or dividing (descending) the frequency of the previous pitch by the twelfth root of two (approximately 1.059463).
Because of that, all notes with these kinds of relations can be grouped under the same pitch class and are often given the same name. The top note of a musical scale is the bottom note's second harmonic and has double the bottom note's frequency. Because both notes belong to the same pitch class, they are often called by the same name.
Chromatic scale drawn as a circle The diatonic scale notes (above) and the non-scale chromatic notes (below) [2] The twelve notes of the octave—all the black and white keys in one octave on the piano—form the chromatic scale. The tones of the chromatic scale (unlike those of the major or minor scale) are all the same distance apart, one ...
The size of an interval between two notes may be measured by the ratio of their frequencies.When a musical instrument is tuned using a just intonation tuning system, the size of the main intervals can be expressed by small-integer ratios, such as 1:1 (), 2:1 (), 5:3 (major sixth), 3:2 (perfect fifth), 4:3 (perfect fourth), 5:4 (major third), 6:5 (minor third).
If one starts on any equal-tempered pitch and repeatedly ascends by the musical interval of a semitone, one will eventually land on a pitch with the same pitch class as the initial one, having passed through all the other equal-tempered chromatic pitch classes in between. Since the space is circular, it is also possible to descend by semitone.
For standard A440 pitch equal temperament, the system begins at a frequency of 16.35160 Hz, which is assigned the value C 0. The octave 0 of the scientific pitch notation is traditionally called the sub-contra octave, and the tone marked C 0 in SPN is written as ,,C or C,, or CCC in traditional systems, such as Helmholtz notation.
A pitch class is defined as the set of all pitches that share the same chroma. For example, using the scientific pitch notation, the pitch class corresponding to the chroma C is the set {..., C −2, C −1, C 0, C 1, C 2, C 3...} consisting of all pitches separated by an integer number of octaves.
Do Pitch class mapping with respect to the estimated reference frequency. This is a procedure for determining the pitch class value from frequency values. A weighting scheme with cosine function is used. It considers the presence of harmonic frequencies (harmonic summation procedure), taking account a total of 8 harmonics for each frequency.