"SANFORD, Fla. (AP) -- For a second day in a row, a Florida judge is weighing whether to allow certain voice experts to testify at the trial of a neighborhood watch volunteer charged in the fatal shooting of an unarmed teen.

Circuit Judge Debra Nelson is listening Friday to testimony from voice experts about whether witnesses with expertise in speech identification should be allowed to testify when George Zimmerman's trial starts next week.

Zimmerman is charged with second-degree murder for killing 17-year-old Trayvon Martin during a struggle in a gated community. He is pleading not guilty, claiming self-defense.

Neighbors called 911 during the fight and cries for help can be heard on the recordings.

Martin's family claim the cries came from the teen while Zimmerman's father has testified they were those of his son.'