Altissimo sax notes require a tuned vocal tract resonance just above the pitch.

Evidence

In the high (altissimo) range, professional saxophonists systematically tuned a strong tract resonance slightly above the desired note. Without this trick, amateurs were unable to play notes in that range. — Eric J. Heller, Why You Hear What You Hear- An…, 1620

Categorization

• XREF: Connects to voice/vocal tract material in the next chapter and to the earlier chapter on how the ear/mouthwork as shaped resonators.