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Archive for May, 2011
Recently I was asked to listen to 23 phone intercept recordings and determine if any of the voices in these conversations were repetitive. As an audio forensic expert, when I conduct a voice identification test, I have to have an exemplar or voice sample of the accused.
Back to back voice samples are the first step to a task like this. Each telephone conversation included two voices. The first thing I did was separate the voices and create two new audio project files. That way I can critically listen to all voices back to back in order to determine if any of the voices were identical or at least had similar characteristics.
These telephone recordings were created by federal law enforcement and were very clean. No noise reduction was necessary because the recordings were created back in the analogue days.
Once I completed this back to back assembly process, I had the recordings transcribed so I could choose phrases and sentences to use when creating the exemplar. An exemplar is a known sample of speech recorded as exact as possible to the original evidence. The exemplar is created under supervision so I know the identity of the person speaking (who is the accused).
When the exemplar recording is complete, those phrases that were recorded are now inserted into the original evidence recordings in the new audio project files for critical listening. In this particular case, I noticed that the exemplar did match some of the telephone conversation evidence that was recorded by the federal authorities.
The next step is to create work notes listing all the similarities as well as differences observed during the critical listening phase of the voice identification testing. These notes help me create my report when the voice identification testing is complete.
I also use spectrum analysis and sonograms to help with the identification process. I often print out the display of these two electronic measurement devices and include these print outs with my report.
One thing I have learned over the 25+ years as a forensic expert: keep it simple. Judges like a non complicated decision from a qualified forensic examiner. They become frustrated when they have to interpret new information they have never heard of or are not familiar with.
Voice identification is both an art and a science. As a voice identification expert, I use my talent skill and ability in every case I am assigned to. The science is acceptable in court and the art is the ability to adapt every case to scientific standards.
An audio exemplar is an audio recording that is created by the audio forensic expert and will be used as a comparison to the evidence for the purpose of identification. Unlike the original evidence, the exemplar is created in a controlled environment. If the original evidence is a telephone recording then the exemplar must be created on the phone as close to the original evidence as possible. If the phone that was assumed to be used to create the evidence is available, that phone should be used to create the exemplar. The goal is to reconstruct as much of the original recording characteristics as possible when recording the audio exemplar. A transcript of the evidence recording must be created to help guide the exemplar recording process. The forensic expert does not notify the accused (defendant) of the portions of the transcript that will be recorded until the scheduled recording time. The reason for this is to have the ability to be spontaneous and unrehearsed when creating the exemplar. The exemplar comparison call is scheduled between the lawyer, audio forensic expert and the defendant. If the defendant is incarcerated the prison is involved in the coordination so the call can be recorded from the prison. In this case, the identity of the person delivering the exemplar is known. If the defendant is not incarcerated, then a neutral party or witness must be present to swear to the identity of the person making the exemplar recording. A representative from the court of law or a law enforcement official would be a good witness. The call is recorded by the audio forensic expert using an electronic telephone interface device manufactured by Gentner. Other companies manufacture similar devices but we use the Gentner SPH 10 in our forensic lab. We also use Sony Soundforge software to record the exemplar and conduct the voice identification testing. The call begins with the forensic expert explaining to the defendant the voice tone necessary when delivering lines from the transcript for recording purposes and continues to guide the exemplar recording process. Its best to have the defendant read each sample three times giving the expert options when conducting the testing. Double check the recording quality by monitoring the telephone recording both during and after the exemplar creating process is complete especially if the defendant is incarcerated. Once a reliable exemplar has been created, the audio expert can begin the voice identification process. If multiple telephone conversations are submitted as evidence, an exemplar should be created of each conversation. Creating a high quality exemplar under supervision is probably the most important part of the voice identification process. If there are other recorded conversations that include the defendant’s voice but are not the exact words used in the evidence recording, they can be used as comparison. Be cautious in the voice identification testing as this is not as desirable of a testing as having an exact exemplar. In this case the voice identification expert must rely on their skills to substantiate the reasoning and their conclusion more so than when an exact exemplar has been created.
This distance learning program includes all the training you will need in order to become a professional voice identification examiner including 4 one-on-one training sessions and a distance learning kit (which include three exams and two actual voice identification cases you need to complete in order to earn the certification).
Program cost includes course study guide, workbook, 4 one-on-one training sessions with Ed, two actual voice identification cases, tests and certification. It’s about a 10 week program. Program includes voice ID training, certification and information on how to testify in court. At the end you will receive a certificate naming you as a Certified Voice Identification Examiner.