Scheme of phonetics modification

In high notes, the sound of I and U is open.

A – going from low to high notes, the sound changes.
from A to U

O – in low notes, the sound is open but pronounced in the mask.
from O to U

E – in low notes, the sound is open but pronounced in the mask.
from E to I

To channel the sound as explained above means “sharpen the sound”, imagine hundred people that have to pass through a narrow door: this is the phonetics modification.