(ABC News) -- A speech scientist today said it was "imaginary stuff" to assert that Trayvon Martin could be heard pleading for help on 911 tapes the night he was killed in a confrontation with George Zimmerman, who is accused of murder in Martin's death.
The testimony came in an unusual court hearing today, in which Zimmerman's defense team called two witnesses in an effort to rebut the testimony Friday of witnesses who said that Martin pleaded for help before he was shot and killed by the former neighborhood watch captain.
The defense questioned the methodology used to detect Martin's supposed howls and pleas on 911 calls made by frightened neighbors who witnessed the fatal altercation on Feb. 26, 2012.
Two forensic analysts said Friday that they detected, one by using a limited voice sample of the Florida teenager, Martin screaming for help on 911 audio moments before he was shot and killed by Zimmerman.
"That's imaginary stuff," speech scientist George Doddington said when asked by defense attorney Mark O'Mara about state witness Alan Reich's testimony that he picked up Martin screaming "I'm begging you" on 911 audio.
Doddington called the methodology used to detect the audio "absurd."
The expected final witness in the hearing to determine whether a jury will hear testimony that Martin screamed for help before he died got stuck on an airport tarmac.
The announcement by Judge Debra Nelson was followed by a court recess that will end with the first day of jury selection Monday as the second-degree murder trial of Zimmerman begins.
ABC News exclusively obtained a sample of Martin's voice and sent the very short sample taken from his cell phone in which he can be heard horsing around with friends to a forensic analyst.
Kent Gibson of Forensic Audio tells ABC News that a comparison of Martin's voice, Zimmerman's voice and the screams on the 911 tape, indicate the voice is more likely to be Zimmerman than Martin. But neither result reach the 60 percent threshold of certainty Gibson said he needed to be assured.
Gibson noted much of the howling and pleading overheard on that 911 tape is muffled or obscured, and that only two seconds of the tape are useable. He said there could not be definitive identification of "the screamer."
In the hearing today, Doddington testified that ultimately humans can tell the difference between voices better than any machine. The state's counter-argument was that the jury should be presented with all sides and make the decision for themselves.
After the the hearing today, the defense filed yet another motion asking that the start of the trial be delayed.
Unless the judge grants the request the Frye hearing will resume after a jury of six is selected. The process to find that group of men or women along with four alternates will begin Monday. There were 500 notices sent out in March across Seminole County, Fla.
The names of potential jurors in the trial will be kept confidential. In court they will be referred to only by jury number.
Nelson also ruled earlier that potential jurors will not be sequestered. It is estimated that the process of jury selection will take anywhere from one to three weeks. Of course, finding 10 people who have heard little about this controversial, highly publicized case won't be easy.
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