How does he do his high screams, for example at the beginning of BYOB.

http://youtube.com/watch?v=B3Az7JPZ6ZA

About 25 seconds in that video.


How does he do his low screams, for example near the middle of ATWA.

http://youtube.com/watch?v=xZdL1BupbhU

About 1 minute 40 seconds into that video