Brass playing drives the lips above their natural vibration frequency.

Evidence

We have concluded that blown closed reeds need to be played below their natural oscillation frequency, and blown open reeds need to be played above their natural oscillation frequency. In the trumpet, trombone, and so on, the reed (the lips) needs to vibrate naturally at a lower frequency than the air column, so that the reed is being driven well above its resonance frequency. Then, the reed is open at high pressure, the resonance is self-sustaining, and the air column is active. Case solved. — Eric J. Heller, Why You Hear What You Hear- An…, 1617

Categorization

• XREF: connects to: Brass instruments operate acoustically as stopped-end tubes driven by lip reeds — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 1234