Shape consists of several different factors:

1. Tongue position – the tongue arches as you ascend. Here I am afraid of giving bad advice, but it feels like the middle rises and slightly. I think the arch goes somewhat toward the teeth in the extreme high register. Our jaws are tied to our tongues and as my tongue goes down my jaws pull it down because I slightly drop my jaw. The jaw slightly closes with higher pitches as my tongue arches up.

2. Aperture corners – This is a slight tension at corners of the aperture. Which is different than clamping the middle. An aperture is formed by doing the AAH – OOH and you see this large opening, a great size for playing low notes. As you ascend the aperture gets smaller by the lips slightly tightening from the sides and not in the middle. For me, this is so tied with the tongue arch. My lips seem to respond to the tongue arch. I like the way John describes it as tightening toward the air column.

These factors work together. Changing the aperture size and changing the oral cavity’s shape will change pitch. The back of your throat needs to stay relaxed and opened.