# Alpharabian comma

The **Alpharabian comma** (about 9.18177¢), is the interval **131769/131072** or [-17 2 0 0 4⟩ in monzo notation. It is the amount by which a stack of two 128/121 diatonic semitones falls short of a 9/8 whole tone. The term "Alpharabian" comes from Alpharabius- another name for Al-Farabi- and was chosen due to the fact that 33/32, also known as the the Al-Farabi Quartertone, is the primary limma of the 11-limit, a fact which lends itself to the idea of just 11-limit tuning being called "Alpharabian tuning" in the same way that just 3-limit tuning is called "Pythagorean tuning". Given that the Alpharabian comma and the Pythagorean comma are similar in that both commas represent the difference between two of their respective p-limit's primary diatonic semitones and a 9/8 whole tone, it follows that tempering out the Alpharabian comma results in a member of the **Alpharabian family**.