RE: Orchestral-Instrument Aperiodicity

>4. Since the entire wave does not move up and down with this curve, this
>can't
>be due to a subharmonic. (Also, it was run through a subsonic filter before
>being drawn here, and this particular pitch is in the lowest register of
>the bass clarinet, so it subharmonics are inherently unlikely.)

It looks an awful lot like the true fundamental is an octave below the
period you have identified. Read Benade or Backus, one of whom discusses
how the true fundamental can indeed be a subharmonic of a resonant
frequency, a phenomenon found not only in wind and brass instruments but
also the human voice (e.g., Tuvan throat singing, Janis Joplin). Your
subsonic may have lessened that true fundamental, but it is still there.

>11. The troughs circled in green MAY reflect the peaks and troughs of a high
>harmonic walking through that particular slightly-lower-harmonic-dictated
>trough. I'm not sure of that by any means though.

We both forgot to mention noise. All wind instrument timbres contain
significant amounts of noise, coming from the breath of the performer
while the reed is open. This noise will of course spoil any exact
periodicity that might otherwise be there. By the way, the instrument
will tend to amplify this noise at its resonant frequencies. Try playing
a wind instrument without the reed and you will still get a rough idea
of the pitches you're fingering from the way your breath-noise is
amplified.