Tetrachord

A tetrachord ( ancient Greek for " Four Note ") is a Viertonfolge with the frame interval of a perfect fourth. The term is taken from the music theory in ancient Greece and is occasionally used to this day to explain the construction of scales. Of the various customary in ancient Greece forms only the so-called diatonic tetrachord has been found in Western music theory entrance. This tetrachord consists of two whole tones and a semitone together, with the following variants are possible: whole tone whole tone - semitone, whole tone whole tone - semitone - whole tone - whole tone and semitone.

The classic diatonic scales ( major, minor, church modes ) can be composed with the addition of another whole tone from two identically structured tetrachords, provided one applies the same conditions that were the ancient Greek scales based. Two cases must be distinguished:

• In the C major scale ( CDEFGABC ), the two unconnected tetrachords have the interval structure: whole tone - whole tone - semitone. Between the first tetrachord ( cdef ) and the second ( gahc ) is the whole step fg.
• When a natural minor scale ( ahcdefga ) the two tetrachords have the structure: whole tone whole tone - semitone. The first tetrachord ( ahcd ) d is connected with the second ( defg ) by the common tone and above, an additional whole step ga is added.

In looking to lay or student textbooks of facts is sometimes represented differently. A general music theory, for example, describes the minor scale as consisting of two unconnected tetrachords composed: " In contrast to the major scale, therefore, the two tetrachords of the minor scale are built differently from one another. "

History

Ancient Greece

Main contribution → The sound system of ancient Greece.

In the music of ancient Greece were also the chromatic and enharmonic as the Tongeschlechter next to the diatonic scale. However, these are not the same as our current terms of diatonic, chromatic and enharmonic one.

The tetrachord played an important role in the music theory of ancient Greece. In the diatonic tetrachord was the initial sound of a whole step, another whole step, and finally a half step down. The semitone was always at the bottom of Tetrachordes. On the white keys of the modern piano, there are two such ancient Greek tetrachords: EDCH and AgFe. Put together, these two tetrachords a descending diatonic ladder. The joining of tetrachords was a fundamental idea in the music theory of ancient Greece. In addition to the diatonic tetrachord, there was also a chromatic tetrachord with the step sequence minor third, semitone, semitone and an enharmonic tetrachord with the step sequence major third, quarter tone, quarter-tone. Some of the earliest sources on the tetrachords go back to Greek philosopher and mathematician. More information can be found in the descriptions of the Greek philosopher and mathematician. Philolaos - Section music theory, Archytas - Music section, Aristoxenus - section harmonies, Euclid - Section music theory.

Middle Ages

Music theorists of the Middle Ages, especially the influential Hucbald of Saint- Amand, resorted to the ancient Greek tetrachord concept, but in a different form. Now the Viertonfolgen you turned not before descending, but ascending, limited to diatonic ratios, placing the semitone not only down, but optionally at the bottom, in the middle or top. The tetrachords obtained were extended to Hexachorden or, as in Ancient Greece, combined to modal fibers, the so-called church scales. So was the church mode Doric of two tetrachords with the step sequence whole tone, semitone, whole tone ( on the white keys of the piano: defg and ahcd ).

20th century

In the 20th century ethnomusicologist took over the term. They called excerpts from pentatonic ladders with the frame interval of a fourth " tetrachords ", although these excerpts were not four but only three tones. Two three-note " tetrachords " formed a pentatonic scale ( the black keys of the piano, for example, cis -dis - fis and gis ais -cis). In this meaning, the Tetrachordbegriff was especially used to explain Japanese sound systems, such as by Fumio Koizumi.

References and Notes

• Musical theory