Re: Brass instruments

[John Denker <jsd@MONMOUTH.COM>]

At 06:14 AM 7/8/99 -0400, John Cooper wrote:
>   The vibration of the lip that brass players use to initiate the sound
> sounds not unlike the 'breaking of wind', absent a mouthpiece, horn and
> accoutrements.  The lip can be tightened muscularly or loosened to shift
> the maximum in the vibrational spectrum of the input to the mouthpiece but
> it is definitely a broad spectrum emission.  The 'tone' of a beginner
> sounds funky compared to that of an experienced player because the latter
> is more skilled at approximating the input spectrum's maximum to the
> desired output, but even a Maynard Ferguson's input was a spectrum broad
> enough to make its 'pitch' indeterminant.

Hmmm.  If I'm interpreting this correctly, you are suggesting modelling the
horn as a broadband excitation (the lips) followed by a filter (the horn
and accoutrements).

I suspect that's not the whole story.

As I understand the physics, there is a standing wave in the horn.  At
cycle N, the standing wave contains energy it received from earlier "pops"
of the lips.  The trick is that there's a feedback effect:  the standing
wave itself makes a contribution to determining when the Nth "pop" occurs.

This contribution is not 100% determining, but it's pretty big.  Otherwise
it would not be humanly possible to play in tune.

The opposite extreme (broadband excitation plus filter) can be observed in
other situations.  For instance, you can make a bronx cheer in the shower.
If the excitation (or a harmonic thereof) is close enough to resonance of
the enclosure, you will get a big response, but since the shower has a bad
impedance mismatch to the lips, there will be no feedback effect, and the
more typical result is an out-of-tune, low-amplitude response.

Right?

Cheers --- jsd