The intervals of the diatonic, enharmonic, and hard chromatic modal genres in Byzantine music theory approximate more or less to the corresponding intervals on an equal-tempered keyboard. The same, however, cannot be said for the intervals of the soft chromatic genre, which is used for the second mode and for some heirmologic settings in the fourth and second plagal modes.

In order to clarify interval differentiation with respect to the soft chromatic "scale," [*] reference here will be made to the modern system of "cents," which divides the octave into 1200 elements; each semitone, or half step, consisting of 100 cents.

In the following chart, the intervals of a scale with equal temperament (the standard for most contemporary Western music) appear, measured in cents, on the upper row. Below are the intervals of the soft chromatic scale, using the note C as a theoretical "Νη" ("Do").


Click here to listen to a soft chromatic chant
that begins with the notes: G-A-B-C-B-A-G (165 KB)

A comparison of the two sets of measurements makes evident the discrepancies between the 2nd and 3rd, 3rd and 4th, 5th and 6th, 6th and 7th, and 7th and 8th degrees. Most of these intervallic disparities are insignificant, as with D-E, E-F, A-B and B-C (each has a differentiation of 33 cents). The principal difficulty, however, lies with the soft chromatic "A." If equated with either A-natural or A-flat of the equal-tempered scale, either the interval G-A or A-B will diverge from its proper value by 67 cents. It is recommended, therefore, that, in general, the soft chromatic A be preserved as natural except when the melody oscillates between G and A (without ascending to B), in which case it should be flattened.  Adherence to this rule (admittedly arbitrary) will go a long way in conserving the ethos of the soft chromatic modal genre.

When a melody modulates to the soft chromatic in this book, the accidentals are introduced, as indicated, in order to approximate the intervals of that genre. But for those who desire and are able to sing the exact intervals of the soft chromatic modal genre, the Byzantine musical symbol  is attached to Δι (Sol) (which is not always G) in order to identify where the alter­ation begins. Note that this symbol is not used for hymns that begin in the second mode, since for them G always corresponds to Δι of the soft chromatic scale. When the melody reverts from the soft chromatic modal genre to a mode that can acceptably be accommodated by regular accidentals, the appropriate Byzantine music symbol is used.

[*]Strictly speaking, it is incorrect to refer to the eight divisions of the Byzantine oktoechos as "scales." While some of their musical gestures are reminiscent of those in modern Western scales, the Eastern melodies, like their counterparts in the old Latin musical repertories, behave in ways entirely alien to contemporary scale-based tunes.  In order to differentiate between the two, chants are said to belong to one of the eight "modes." (vid. Harvard Dictionary of Music, Revised Edition, Cambridge, Massachusetts, 1970, pp. 753-4.)
For a simplified explanation of the Byzantine musical system, see:

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