A term from Mehdi Barkeshli to designate the interval measurement unit used by al-Farabi.
A farab is ~8.3333 cents, or exactly 8 1/3 cents.
A farab is calculated as the 144th root of 2 -- 144√2 or 2(1/144) -- with a ratio of approximately 1:1.004825126, which is an irrational number. This interval therefore divides the octave, which is assumed to have the ratio 2:1, into 144 equal parts. Thus a farab represents one degree in 144-edo tuning.
The familiar 12-edo semitone is equal to exactly 12 farabs, since 144 divides evenly by 12 exactly 12 times.
The formula for calculating the farab-value of any ratio is: farabs = log10(r) * [144 / log10(2)] or farabs = log2(r) * 144, where r is the ratio.
Barkeshli, Mehdi. [date]