Arabic modes

I've recently been lurking on the USENET newsgroup rec.music.arabic
hoping somebody would say something interesting about scales and
tuning instead of mostly inquiring about CD's of popular performers, etc.
Anyway, the FAQ was distributed this AM and I extracted the following
information on scales:


Mode: Tone spacing
----- ------------
rast: 1 3/4 3/4 1 1 3/4 3/4
sikah: 3/4 1 1 3/4 3/4 1 3/4
@ajam (Major): 1 1 1/2 1 1 1 1/2
@ajam (Minor): 1 1/2 1 1 1/2 1 1
alkird: 1/2 1 1 1 1/2 1 1
alhijaz: 1/2 1 1/2 1/2 1 1/2 1 1
bayati: 3/4 3/4 1 1 1/2 1 1
Saba: 3/4 3/4 1/2 1 1/2 1/2 1 1

One can see how tetrachordal these modal scales are. Rast is clearly
two tetrachords of the form 200 + 150 +150 cents and would appear to
be related to Ptolemy's Equal Diatonic. One could also analyse this
scale as a mode of a scale composed of two 150 + 150 + 200 cent
tetrachords, but I think the first form is more likely true as it
preserves the neutral third. Sikah is a mode of this scale. The next
two, @ajam, are the major and minor modes of the diatonic while Alkird
is the Dorian. Alhijaz is a mixture of Neochromatic and Diatonic
tetrachords, Bayati of Equal Diatonic and Diatonic, while Saba is
a mixture of Equal Diatonic and Neochromatic.
The quantization to 24-tet obscures the exact tuning somewhat,
but it probably captures the general impression actual performed versions
make.

--John


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