[RichD]

What is the physics/acoustics of a wind instrument?

It's easy to see how a percussive surface vibrates, and
induces acoustic waves at the same frequency.
Ditto a string.

But pushing air through a trumpet (sax, etc.), then out
the bell - how does that create sound? And in particular,
how does the valve action produce controllable wave
sequences (a/k/a music)? It's just air on air, I'm at a
loss to explain it.

--
Rich