| 21. | In practice, a jins ( pl . ajnas ) is either a trichord, a tetrachord, or a pentachord.
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| 22. | The exact proportions which divided a tetrachord, had never been a subject of Greek medieval treatises concerned about Byzantine chant.
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| 23. | This tetrachord, treated as a very short ground bass, is repeated again and again over the length of the composition.
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| 24. | The tonal structure of some of these songs revolves around a minor third, while others are built on a major tetrachord.
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| 25. | In the late 9th-century, Hucbald included it as the lowest note of the first tetrachord of his scale system.
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| 26. | A row created in this manner, through variants of a trichord or tetrachord called the generator, is called a derived row.
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| 27. | In these measures, the right hand features D, E, and G, the tetrachord without the 3rd ( F ).
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| 28. | These are the proportions, presented as a division of a tetrachord using the proportions of 22 : 21 and 7 : 6:
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| 29. | These various sizes of incomposite interval depend on the genus of the tetrachord, as explained by Nicomachus in the first century AD:
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| 30. | Modern music theory makes use of the octave as the basic unit for determining tuning : ancient Greeks used the tetrachord for this purpose.
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