Fixed vocal tract whistles hold pitch while cavity-free jets rise in pitch with airflow

Evidence

If the mouth, tongue, and vocal tract are kept absolutely rigid, the pitch of the whistle changes very little as less or more air is forced through. although it may jump to a new mode of the vocal tract at higher velocity. This is not true of cavity-free jet vortex formation, such as happens when a window is cracked open in a breeze; this increases in pitch as the air is forced more rapidly. — Eric J. Heller, Why You Hear What You Hear- An…, 1333

Categorization

• CANDY: Counterintuitive and easy to demonstrate: a rigid-mouth whistle barely changes pitch with breath force, but a cracked window ‘whistles’ higher as wind rises.
• corroborated: 2 independent passages support this claim — Eric J. Heller, Why You Hear What You Hear- An…, 1333
• XREF: connects to: Resonator pitch scales with gas speed, volume, neck geometry; Whistle pitch derives from vocal tract resonances, not the oral cavity’s Helmholtz resonance — Eric J. Heller, Why You Hear What You Hear- An…, 1324; Helium and sulfur hexafluoride change voice timbre, not pitch