I've heard how sure some of these people are. (I think Boobie said he would swear on a stack of bibles that it was Trayvon.) But I haven't heard of a single one that claims he heard the subject scream like that before or who picked the screams out of a lineup. And we demand a Frye hearing for scientists but nothing for these kind of witnesses? The fact that West wrote a memo shows how much depends on calculations involving how dumb a jury they will get versus getting good evidence.
IIRC, Robert Zimmerman, Sr. said, under oath, that he'd heard his son George scream for help before.
"It was absolutely George's" voice screaming on the tape, his father testified, saying he had heard his son yell "many times" before.
Clashing views of Zimmerman arise in bail hearing - Miami Herald - 29 June 2012
The experts come to the case without any familiarity with the various speakers, beyond what they are given for evidence to work with. The Frye test just flat out doesn't apply to a fact witness, because the fact witness isn't depending on the application of science, technology, or specialized expertise. That doesn't mean a fact witness can't be challenged as having insufficient basis for the statement. Cutcher, for example, didn't see the altercation, and doesn't know the natural voices of either Martin or Zimmerman, but she claims Martin was the screamer because the screams sounded like a little boy, and she saw Zimmerman standing over Martin some half a minute or more after the shot was fired.
West's motion was well taken, because it aims to use the power of the court to prospectively force the state to disclose specific exculpatory evidence. It also informs the state that the defense is interested in the conclusions of at least one other fact witness who may be qualified by familiarity with Martin's voice - Witness 8.