C major scale
Played on the piano.
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All the notes of the scale of C major are separated by a tone, with the exception of the pairs E-F and B-C.
Tones and semitones are easily visualizable on keyboard instruments. A tone is the interval between two white keys separated by a black key. A semitone corresponds to the interval between two white keys without being separated by a black key.
There are two types of semitones: the diatonic semitone and the chromatic semitone. It takes a diatonic semitone and a chromatic semitone to form a tone.
The diatonic semitone is the smallest interval separating two conjunct notes. It measures only 4 commas. The diatonic semitone always involves two notes with different and contiguous names (hence its qualification of dia-tonic, "of separate tones")
A tone is formed of a chromatic semitone and a diatonic semitone. It therefore has a total of 9 commas.
The octave is the smallest interval that separates two notes with the same name. For example, between two Cs, there is an octave.
An octave is thus formed by 5 tones and 2 diatonic semitones (see Figure 1 at the beginning of the course). Since a tone itself consists of a chromatic semitone and a diatonic semitone, the octave is thus formed of 12 semitones, of which 5 chromatic semitones and 7 diatonic semitones.
Since the XVIIth century, Western music has adopted the system of equal temperament. The octave is divided into twelve equal semitones. These semitones, whether diatonic or chromatic have the same pitch difference in the ear. A tone is no longer divided into 4 + 5 commas but 4.5 + 4.5 commas. This technique allows, with a small concession to accuracy, to greatly simplify the tuning of keyboard instruments, which previously were tuned according to the key signature of the work that was to be interpreted. Since the appearance of the equal temperament, it is possible to play in any key on a keyboard instrument.
However, some contexts (eg for string instruments) need to take into account the difference between chromatic and diatonic semitones. Moreover, at the theoretical level, their differentiation is essential because it allows to understand many concepts such as the construction of scales or the qualification of the intervals, which is why, whatever the temperament used, it is important to be familiar with the concepts mentioned in this chapter.
Last update on 2018/12/03
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