next stage of development: apophony (ablaut)

I'm going to incorpoarte apophony/ablaut into Tech, based on existing
systems found in Afro-Asiatic and Indo-European. So I'm looking for
information on that -- and a comparison and a contrast of both language
families in that area.

(Proto-Noachian, the parent language of Tech, had six short vowels, which
were reduced to two /@~a/ in Tech with residual palatization and
labialization where /i~e/ and /u~o/ existed, but the same six-vowel system
re-emerged due to grammatical apophony. There are also numerous "complex
vowels" resulting from mergers of vowels with certain following consonants,
producing long vowels, "umlauted" long vowels, nasal vowels etc.)