The Upper Register of the Oboe
One of the ways of achieving the upper register of the oboe is opening a hole in the side of the air column close to the mouthpiece. Opening a hole releases excess air pressure and destroys the fundamental vibrational mode. If properly positioned, the hole favors the second harmonic mode which has a pressure node (displacement antinode) in the region near the mouthpiece.
One of the mechanisms for register change is a key with a hole in it which is kept covered with a finger of the left hand when playing notes in the lower register. The upper register can be achieved by lifting the finger from this hole as demonstrated above.
Thanks to Liz McKeown for helping to demonstrate the instrument and to Tim Merritt of GSU's Instructional Resource Center for assistance with the video.