The 911 call audio recorded during a fight between George Zimmerman and Trayvon Martin contains yells for help.  Determining if Zimmerman is the voice on the recording could affect the defense argument that Zimmerman was defending himself when he shot Martin.

There was a Frye hearing to decide whether audio experts on the side of the prosecution were using science and techniques that are proven for use in court.

Here is a link to the judges very thoughtful and interesting decision to prevent prosecution forensic audio experts from testifying that Zimmerman is definitely NOT heard yelling for help.

JUDGES FRYE HEARING DECISION TO EXCLUDE PROSECUTION AUDIO EXPERTS
http://media.miamiherald.com/smedia/2013/06/22/11/12/eppN3.So.56.pdf

Below are YouTube links from audio forensic expert witnesses testifying at the George Zimmerman Frye hearing regarding the admissibility of prosecution expert witnesses. Witnesses for the prosecution were planning to testify that Zimmerman is NOT the person heard yelling on the 911 calls, and the defense claimed that the science and technology they were using was unproven and confusing.

This is an amazing collection of expert witness testimony.
Thank you YouTube!

FOR PROSECUTION:
Dr. Alan Reich Part 1: http://www.youtube.com/watch?v=qlnkSNoXZUE

FOR DEFENSE:
Dr. Peter French & Part 1 of Dr. George Doddington: http://www.youtube.com/watch?v=UT871ae_M2Q
Part 2 of Dr. George Doddington: http://www.youtube.com/watch?v=eVhhp-5h9Xg

Dr. James Wayman: http://www.youtube.com/watch?v=AuNfkt2YRag

Dr. Hirotaka Nakasone: http://www.youtube.com/watch?v=SNDHriX1AHU

REBUTTAL and CLOSING ARGUMENTS:
Tom Owen’s rebuttal testimony, plus both sides’ closing arguments on this Frye hearing (forward the player to 11 minutes, 40 seconds:
http://www.youtube.com/watch?v=zQMx3o8VnYE