ablaut

In an alphabetic system where vocals are not explicitly written, vocalic and other modifications of stems can be realized by determinants

Usually in Sumerian verbs and nouns are inflected via e/i⇨a/o change:
gebe=>Gabe
lege=>Lage
sing=>Song
…
gir⇨gar 𓂻 (pro)gress, walk
sir⇨sar 𓇶 shine
sir⇨sar 🎶 sing/song (germanic r⇨n change)
sim⇨sam 🎶