Vicki self-identifies as a speech pathologist, and maintains that speech scientists have excluded Zimmerman as the screamer because of age. "Science can analyze fundamental frequency which can determine adult vs youth vocal folds."
For the uneducated like me, "vocal folds" are what we commonly call "vocal cords", the strands of tissue inside your larynx, or voicebox. Frequency is determined by mass, the thickness of the fold or cord. How we sing different notes depends on how we can change the shape (stretching or compressing) of the cord while vocalizing, but doing so does not change the actual mass or thickness of the cord/tissue. (Do I have that right, Vicki?)
How could analysis of frequency determine age? Older voices have different frequencies than younger ones. Vicki says that science doesn't lie; and sent me a link to a news article as proof.
Recording of 911 call in Fla. shooting debated (Copyright 2012 The Arizona Republic|azcentral.com. All rights reserved.)
. . . But what happens when a potentially crucial piece of evidence is a poor-quality recording of overlapping voices and unintelligible yells, essentially a wilderness of sound?
The answer may come down to which expert you ask.
One of those experts is Alan Reich.
In an effort to find out what might be discerned from the crucial 911 call, the Washington Post retained Reich, 67, a former University of Washington professor with a doctorate in speech science who has worked for prosecutors and defense attorneys in hundreds of criminal and civil cases over a period of more than 35 years.
Using Sony Sound Forge Pro and KayPentax Multi-Speech software, he identified certain sound segments he wanted to examine more closely, such as the yell in the first second of the recording.
The yell in the first second of the recording, Reich concluded, was actually a four-syllable phrase: "I'm begging you." The yell in the very last second before the gunshot was a word that the spectrograph indicated began with a "st" sound, followed by an "ah" sound: "stop."
Reich measured a particular frequency of the "ah" sound, which he said corresponds to certain anatomical factors in the speaker, such as the length and diameter of the vocal tract, as well as speaking style. This frequency, he said, was "highly appropriate for a 17-year-old male" who was still growing.
Throughout the 45 seconds the voice Reich believes to be Martin's was "extraordinarily stressed, frightened and desperate," he concluded.
Reich discerned a second voice in the background, one that was much more difficult to tease out. He amplified those segments, analyzed them and compared the patterns to Zimmerman's vocal patterns on his earlier call.
Reich concluded this voice was the older of the two speakers, Zimmerman.
Voila! @Vicki627's proof!
But then the article continues:
Another way to consider the 45-second recording is the way James Ryan considers it.So, Sorry @Vicki627. Not buying it. Two "experts". Two opinions.
Ryan is the retired head of the FBI forensic audio, video and image analysis unit. He said even the best audio forensic expert using the most sophisticated equipment available would have a difficult time determining much at all from a recording of such degraded quality.
Ryan, who has testified against other audio-recording experts in trials, was asked to point out what he considers to be the vulnerabilities in any expert analysis of the 45-second recording.
Listening to the 45 seconds, what Ryan hears is problems.
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.
The science is useful as an investigative tool, Ryan said, but limited in its usefuless in this type of audio recording.
Ryan also questioned the idea that the age of the person or persons screaming during the 45 seconds can be determined by measuring frequency, or pitch.
"The science doesn't help with a recording like this," Ryan said. "There isn't anything to hang your hat on."
Reich compared the 911 call to Zimmerman's earlier call. Zimmerman's voice in the earlier call was pretty calm and level. When a person is screaming while "extraordinarily stressed, frightened and desperate," the qualities of the voice change. It's pretty much comparing apples to oranges. The FBI concurs:
Trayvon evidence fails to answer who screamed for help (Reuters)
An FBI expert found crucial evidence in the Trayvon Martin case was inconclusive, saying it was impossible to tell if the voice screaming for help belonged to the black Florida teenager or his shooter George Zimmerman just before the neighborhood watch captain pulled the trigger.
Nonetheless, @Vicki627's opinion is that the voice screaming has been established to be a younger voice, because of scientific application of fundamental frequency differences caused by age. Frequency depends on the mass of the vocal fold. The folds thicken with age.
The way I understand it, thicker, shorter vocal folds create deeper sound, a lower frequency. Thinner, longer vocal folds create higher tones/frequency.
Are there differences in the vocal folds between races? And if so, how would that affect the outcome of an analysis looking only for typical differences of age?
I don't have a scientific paper to link to, but just by googling for it, there are several articles discussing how the Negro race has thicker, shorter vocal cords than Caucasian, and that Orientals have even longer and thinner than the other two. Mostly, these articles are about music, singing, and vocal coaches. Perhaps @Vicki627 can find a properly credentialed paper.
We could get into a huge conversation about physical differences and characteristics of different races of people, but Vicki informs me that we are all the same, and there are no anatomical differences between any race.
My theory is that Trayvon's thicker, shorter vocal folds are going to emit a frequency that compares to an older person; and that George's thinner, longer vocal folds are going to emit a frequency that compares to a younger person. And that if Mr. Reich did not take racial differences into account when making his study, that his science is suspect.
But, what do I know? @Vicki627 says I don't know science.