Information AboutTetrachord |
| CATEGORIES ABOUT TETRACHORD | |
| music theory | |
| simultaneities | |
| chords | |
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; Diatonic :A diatonic tetrachord has a characteristic interval that is equal to, or less than half the total interval of the tetrachord (or 249 Cent s). This characteristic interval is usually slightly smaller (approximating to 200 cents), becoming a Whole Tone , Classically, the diatonic tetrachord consists of two intervals of a tone and one Semitone . ; Chromatic :A chromatic tetrachord has a characteristic interval that is greater than half the total interval of the tetrachord, yet not as great as four-fifths of the interval (between 249 and 398 cents). Classically, the characteristic interval is a Minor Third (approximately 300 cents), and the two smaller intervals are equal semitones. ; Enharmonic :An enharmonic tetrachord has a characteristic interval that is greater than four-fifths the total tetrachord interval (greater than 398 cents). Classically, the characteristic interval is a Major Third (otherwise known as a ditone), and the two smaller intervals are Quartertone s. As the three genera simply represent ranges of possible intervals within the tetrachord, various ''shades'' ( Chroai ) of tetrachord with specific tunings were specified. Once the genus and shade of tetrachord are specified the three internal intervals could be arranged in six possible permutations. Modern music theory makes use of the . Ancient Greek music always seems to have used two identical tetrachords to build the octave. The single tone could be placed between the two tetrachords (between Perfect Fourth and Perfect Fifth ) (termed ''disjunctive''), or it could be placed at either end of the scale (termed ''conjunctive''). Scales built on chromatic and enharmonic tetrachords continued to be used in the classical music of the Middle East and India , but in Europe they were maintained only in certain types of Folk Music . The diatonic tetrachord, however, and particularly the shade built around two tones and a semitone, became the dominant tuning in European music. The three permutations of this shade of diatonic tetrachord are: ; Lydian Mode :A rising scale of two whole tones followed by a semitone, or C D E F. ; Phrygian Mode :A rising scale of tone, semitone and tone, C D E♭ F, or D E F G. ; Dorian Mode :A rising scale of a semitone followed by two tones, C D♭ E♭ F, or E F G A. Medieval music scholars misinterpreted Greek texts, and, therefore, mediaeval and some modern music theory uses these names for different modes than those for which they were originally intended. Arab and Indian music divide the tetrachord differently than the Greek. For example, Al-Farabi presented ten possible intervals used to divide the tetrachord (Touma 1996, p.19): Since there are two tetrachords and a Major Tone in an octave, this creates a 25 tone scale as used in the Arab Tone System before the Quarter Tone Scale . In Musical Set Theory , a tetrachord is a Collection of four Pitch Class es, often one of the three ordered tetrachords in a tone row or set form. Tetrachords may be used to create Derived Row s and Invariance . SEE ALSO SOURCE
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