|Acoustics of the saxophone
Bb tenor saxophone
Notes are the written pitch.
This is the fourth note in the altissimo or very high range. It is not a member of a simple register: it plays at the third 'large-ish' peak, or the sixth peak, but we should rather say that it is just a cross fingered note whose operating peak falls above the cut-off frequency and so cannot readily be described in terms of an effective length.
The weakness of this peak (due to the relatively large cone angle of the saxophone) explains why notes in this range are hard to play and require the player to assist the weak impedance peak of the bore with a strong impedance peak of the vocal tract. See this page for an explanation and some interesting results.
This sound spectrum includes some transient excitation, and so has traces of a subharmonic being excited, seen in the range above about 2 kHz.
Sound spectrum of a Bb tenor saxophone played using fingering for A#6.
For more explanation, see Introduction to saxophone acoustics.
You can hear A#6 played.