( CNN ) -- Two days before George Zimmerman goes on trial , voice recognition experts testified it is not possible to positively identify whose screams are heard in the background of the 911 calls made the night Trayvon Martin was shot . Florida Judge Debra Nelson will continue the hearing on the admissibility of the experts ' testimony at a later date . Jury selection begins Monday . A third audio expert was unable to testify Saturday because he was stuck on a plane . The defense argues the state 's audio experts are using unproven science to determine who is heard screaming and they should n't be allowed to testify . Nelson wanted to hear about the technology used for voice analysis . Trayvon Martin shooting Fast Facts . Forensic audio expert Dr. Peter French , who testified via teleconference from the United Kingdom , described research involving the recording of stressed cries versus normal voice samples . In the case of the 911 calls , French said that the poor quality of the recorded voices means that none of the processes available can provide any useful information about the identity of the screaming person . `` I 've never come across a case in the 30 years of my career where anybody has attempted to compare screaming with normal voices , '' French said . French also said in this case the recording `` is n't even remotely suitable for speaker comparison . '' George Doddington , an electrical engineer who works as an adviser with the National Security Agency , testified Saturday that his conclusion about the 911 call was similar to Dr. French 's : that due to the quality of the data , it is not going to provide any viable source for making an identity decision . Doddington said evaluating one second of speech to reach a conclusion is `` ridiculous . '' `` The less you have , the worse the performance , '' he said . Zimmerman , a neighborhood watch volunteer , is charged with second-degree murder in the death of Martin , 17 , on February 26 , 2012 , in Sanford , Florida . He says he shot the teenager in self-defense . The audio technology may be key to the prosecution 's case because its experts ' testimony may be able to shed light on what was said between Zimmerman and Martin moments before the teenager was shot . Alan Reich , a voice analysis expert who testified Friday , believes that the screams recorded were not Zimmerman , but more likely came from Martin . Ted Owens , a forensic audio engineer , testified Friday that his analysis of the 911 call indicated that the person screaming was not Zimmerman , and the person screaming is frantically asking for help in different ways before the gunshot is heard . If the prosecution experts ' analysis indicates Martin screamed for help , it could hurt the credibility of Zimmerman 's claim that he acted in self-defense . The law states that for technology to be admissible , it must be `` generally accepted '' in that particular field . Zimmerman 's attorneys are arguing the technology does not satisfy that threshold .
George Zimmerman trial starts Monday in Florida . Judge considering evidence from 911 calls . Audio experts testify about quality of recordings .