|Acoustics of the clarinet|
Notes are the written pitch.
This curve is more regular than that for G3 or A3 because the 'cross fingering' is less severe: only one downstream hole closed, and it is further away.
For general comments about the chalumeau register, see E3.
Sound spectrum of a Bb clarinet played using fingering for G#3.
For more explanation, see Introduction to clarinet acoustics
You can hear G#3 played.