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Archive for February, 2012
Since I began my career as an audio forensic expert 28 years ago, I have been retained on two drug trafficking cases where the US prosecutors office was trying to convict based on five words spoken during a confidential informant recording.
I have been on both sides of the fence working for the state as well as for the defense. The scientific community, specifically the American Board of Recorded Evidence, explicitly states that in order for an audio forensic expert to deliver a positive identification, “At least 90% of all comparable words must be very similar aurally and spectrally, producing not less than twenty (20) matching words. The voice samples must not be more than six (6) years apart.”
Voice identification is both an art and a science. It is an art in that the forensic examiner has to conform best practices to each specific, unique case. Not all voice identification cases are the same. In fact, I have had related situations but every case has still been unique.
I have identified singers, good guys and bad guys. I have testified in cases where my testimony was crucial in the outcome of the case. One thing remains certain: a government body cannot convict because they believe a specific person said the phrase that their case is built around.
For example, imagine I am with three other friends and after a confidential informant approaches me inquiring about a crime we are plotting, one of us in the group says the “phrase that pays” in order for the CI to complete the sting. Unless that CI’s recording has a 20 or more word “phrase that pays” it’s technically their word against the defendants about who said the convicting phrase.
In other words, the difference between first degree murder and the death penalty vs. a lesser judgment could be that phrase spoken during the recording and the person who spoke that phrase on the CI recording.
An audio forensic expert has the ability to identify that voice by creating an exemplar and comparing at least 20 words, no fewer, spoken by the accused. I recently had a case where the state was going for a more severe conviction based on five words spoken during a CI recording. However, it is not possible to deliver a positive identification based on so few words.
Today, more than any other time in the history of the United States and the world, we find our court systems full of digital audio files in the form of evidence. As an audio forensic expert, I have testified in many cases in the United States and worked on cases in India, Turkey and France. One thing I see time and time again, regardless of geography, is the misunderstanding of how voice identification can aid in litigation.
The American Board of Recorded Evidence here in the United States has established a probability factor with regard to voice identification. This board is a part of the American College of Forensic Examiners International.
When conducting a voice identification test, I look for spectrums that match the recording in question against the exemplar. An exemplar is a comparison recording that a forensic expert creates of the voice in question for comparison purposes. Does each recording include spectrums that are similar?
Even more important are the words themselves. The way the words are pronounced, the pacing of the words pronounced, the space between the words, the articulation of the words and the consistent delivery style are all considered.
No two human voices are the same just like no two fingerprints are the same. Despite attempted voice disguise cover up, a trained forensic expert can identify a voice and compare it to another voice to determine identification.
With experience, a trained audio forensic expert can use voice identification skills in a variety of ways and help uncover the truth behind audio recordings.
In recent months I have used traditional voice identification techniques to identify a new Elvis Presley song, singer in a motion picture soundtrack as well as confirm the difference between a father’s and son’s voice for a civil litigation.
Some would say this is not a proper way to conduct voice identification testing. However, in my humble opinion, with 28+ years of voice identification experience, I believe as long as the audio forensic examiner has experience, an exemplar that is as exact as possible and the necessary tools (hardware and software), nontraditional voice identification is possible.
Using the new Elvis Presley song discovery, turns out that I was right with my positive identification. Two Elvis Presley historians agree with me that this new song is indeed Elvis Presley. After I completed my voice identification testing his record company came forward and confirmed the session date and time the recording was made.
The bottom line is that going forward, voice identification will continue to be an important part of the litigation process when audio evidence is involved. The science is as exact as the expert is experienced. The more experienced the expert, the more solid the expert’s report.