For one, the recording is poor, he said, a problem that Reich also acknowledged. Voices overlap, and there are multiple speakers and banging noises. The caller’s phone might have been unable to pick up all of the sounds outside. Also, the signal from the caller’s phone might have been degraded in quality and might have lost sounds as it was transmitted to the police department’s recording system.
Basic facts such as how far the caller’s phone was from the scene outside are also unclear, so it is difficult to know how distance or reverberations might have affected the recording.
Those problems are compounded when the science of acoustics is applied to degraded recordings typical of crime scenes.
The science is useful as an investigative tool, Ryan said, but limited in its usefuless in this type of audio recording. In this context, its reliability ranks below DNA and below fingerprints and has about the same technical challenges as trying to recognize a face on a degraded surveillance video, he said.
Tools such as spectrographs can bring some measure of clarity to fuzzy sound, and Ryan has used them. But they are vulnerable when it comes to deciphering actual words or phrases, he said.
“People look at those sometimes to determine if it was a ‘k’ or ‘p’ or ‘v’ depending on the restriction and the vocal path,” Ryan said. “But those waters are going to be so murky for this recording.”
“If someone wants to argue that’s the word ‘bun,’ ” he added, by example, “they could find someone to argue it’s the word ‘fun.’ ”
Ryan also questioned the basic idea that the age of the person or persons screaming during the 45 seconds — and thus whether it was 17-year-old Martin or 28-year-old Zimmerman or both — can be determined by measuring frequency, or pitch.
“To my knowledge, there are no scientific studies of pitch as an indicator or anything else in a scream that would give someone confidence to say how old somebody was,” Ryan said.
When it comes to emotionally charged situations, especially a life-or death situation, the range of the human voice is simply too wide and varied to correlate it accurately to age, Ryan said.
A 28-year-old might scream like a 17-year old. A 17-year old might yell like a 28-year-old.
“The science doesn’t help with a recording like this,” Ryan said. “There isn’t anything to hang your hat on.”
How a jury will hear it
After the gunshot, the recording continued as other neighbors began to call 911, look out windows or go outside into the dark to see what was happening. And the vagueness and discrepancies in the accounts they gave only underscored how important an objective recording could be.
At least five neighbors told 911 operators that they had heard “someone” or “a male” screaming.