In the last 24 hours I have received several calls asking my opinion about the voice screaming for help in the background of a 911 call by a woman who heard gunshots outside her home. I was emailed a link to Mother Jones (http://motherjones.com/politics/2012/03/what-happened-trayvon-martin-explained#transcript) and listened to the recordings which I have posted below from AudioBoo.com (http://audioboo.fm/boos/717346-911-call-screaming-and-gunshots-audible)
911 call with male screaming in the background asking for help. Who is the male?
George Zimmerman calling authorities
The male voice in the background can be identified. If I were to conduct a formal voice identification test, here are the steps I would take:
1. Remove the samples of the screaming from the 911 call and isolate them in a digital audio file. Remove background noise and raise the volume of the male screams.
2. Remove portions of George Zimmerman’s voice from the 911 call to serve as an exemplar.
3. Edit both speech samples back to back and compare
4. Ask for a speech exemplar from George Zimmerman screaming for help
5. Conduct a voice identification test.
Do you believe the voice screaming is George Zimmerman, Trayvon Martin or another male?
After a year it’s pretty apparent there were two people present during the Trayvon Martin shooting, Trayvon Martin and George Zimmerman. The question still remains; who screamed for help the night of February 26, 2012, and why is this important?
If it’s Zimmerman who is screaming, it exemplifies that he was the one under attack by Trayvon. If the screaming is Trayvon Martin, then this would add to previously revealed adverse behavior by Zimmerman acting aggressively toward Trayvon. Remember, Zimmerman ignored the police when they told him not to follow Trayvon.
As the State of Florida v. Zimmerman begins to heat up, forensic experts for the prosecution and defense are ready to begin the voice identification testing process to determine who cried for help the night of February 26, 2012.
The human voice is unique to each person and can be examined through the process of voice identification to discover identity. Voice identification testing has become more acceptable in the courts and will be a valuable part of this trial. Scientific processes for voice identification testing include critical listening and spectrographic analysis. Both visual and aural inspection and interpretation of the evidence and exemplar (speech sample of the suspect’s voice) are examined. The problem with this case is the lack of significant speech from the unknown person who cried for help. Voice identification typically requires a minimum of 20 words spoken for comparison purposes. In this case, we are testing screams which is much more difficult.
Yesterday, April 30, 2012, the court has asked experts for the prosecution and defense to produce any enhanced recordings they have of the call to police by Zimmerman. I believe the court is attempting to understand and identify all audio evidence that is available to aid forensic investigators.
So far we have been told that there are no audio or video recordings of Trayvon Martin. Therefore audio forensic experts can only use voice samples, previous recordings, and exemplars that are available to conduct a voice identification investigation and eliminate or identify George Zimmerman as the source of the cries for help based on a degree or percentage of professional certainty.
The first step in any voice identification test is to aurally listen to the evidence and exemplar recordings edited back to back using critical listening skills developed over the course of the expert’s forensic career. In the video below I have edited back to back audio samples taken from the police call by Zimmerman the night of February 26, 2012, when Trayvon was killed and an exemplar or reenactment recording of George Zimmerman created by the authorities.
In a perfect world, audio forensic experts listen for isolated speech sounds like vowels and consonants for their uniqueness, similarities, and differences as well as phrases and sentences. Pronunciation of words are noted, the way words flow together and speech characteristics like accent and dialect, age and gender or nationality are noted.
In this case, the audio forensic expert only has screaming to compare and identify. Yes, this is possible and very important to this case. Based on my experience, the voice identification test results will include a percentage of certainty because of the lack of audio recording and speech available for voice identification testing.