(Greek: "condensation", plurals: pykna, pyknomata, pyknoma)
Intervallically dense region of non-diatonic, i.e., chromatic or enharmonic, genera.
The width of the pyknon is less than or equal to 1/2 of the Fourth.
That is, the widest possible pyknon has the irrational interval-size of 4/3(1/2) [or sqrt(4/3)] = ~1.154700538 ratio = ~249.0224996 cents.
The _pyknon_ indicates 'compression', and refers to the grouping together of small intervals at the bottom of the tetrachord.
Ancient Greek theorists held that each tetrachord in a tuning system was bounded by two fixed notes ('ηστοτησ = hestotes) a perfect-4th apart, and the other two notes inside that 4th were moveable (κινουμενου = kinoumenoi). The pyknon is the group of small intervals found between lichanos and hypate in the chromatic and enharmonic genera:
DIATONIC CHROMATIC ENHARMONIC
A mese ---- A mese ---- A mese ----
G lichanos ----
Gb lichanos ---- \
|
F parhypate ---- F parhypate ---- |pyknon Gbb lichanos ---- \
| Fv parhypate ---- | pyknon
E hypate ---- E hypate ---- / E hypate ---- /
According to Aristoxenos, the higher of these two notes (either paranete or lichanos) could move within the locus of a tone -- i.e., from G down to Gbb in the diagram above, and the lower of them (either trite or parhypate) could move within the locus of a diesis -- i.e., from F down to Fv.
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