that gliss coming down from D can be done by pressing all six fingers down one at a time, but evenly.
you can start the exercise by not even blowing into your horn, just get the steady mechanics of each finger pressing down it’s note, this is all fingers except pinkies. Next try blowing while doing it. If it sounds too much like a weird scale it means your fingers aren’t moving fast enough as it is a pretty quick action where the entire gliss shouldn’t last more than a beat.
The other element to a good gliss is the air… you should almost try and fade out as the gliss gets to the end so the notes aren’t too obvious.
Hope that explanation makes sense!
