music, the octave includes 12 tempered 1/2 tones. The Arabic scales—Maqamat—commonly have diminished octaves which contain only 22 unequally tempered 1/4 tones.
Heterophony: Subjective variations in the details of a single melody when it is performed simultaneously by more than one instrument or voice in unison or coupled octaves.
Subdominant: The fourth degree (IV) from the tonic (I) in a diatonic scale. This tone exists below the dominant (V). In Arabic music, the most important degree is the (IV) not the (V) like in western classical music. This degree is considered a vital tone to construct a melody. Also in the cadence, the melodic line reaches the tonic through the subdominant. (Baroque music might be influenced by this cadence, as in the plagal cadence in Bach’s fugues ).
Neapolitan: A major chord built on the lowered second “supertonic” of the scale in the first inversion (flat II6) or (N6). This chord will called a Neapolitan sixth chord. The traditional Neapolitan chord dates back to the 18th century composers of Italian opera. However, the original Neapolitan chord dates back to both the Maqam Higaz and Kord (similar Phrygian), which was distinguished by the lower second degree.
]]>
Reference:
Lectures of Prof.Dr. Andrew Shenton in jazz course, BU College of Fine Arts, (May-June 2007).