Hamid, you’re right, I think I do that scream a lot. I really love doing it. It’s easy to do but hard to explain…
You would need to have good control of the altissimo register because most of the sound is from up there.
To get started try hitting the highest note you can, then let it fall down and slide back up…repeat this until you are getting the effect you hear me doing.
There is no particular fingering position just move your fingers up and down very fast while at the same time with your embouchure trying to play as high as you can, after hitting the high note let it slide back down using your fingers to control that slide as best you can.
It’s never a sure thing and can sound different each time. anyway, that’s the best way I can explain it without showing you in person.
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