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Are audio forensic procedures reliable?

Wednesday, March 7th, 2012

courthouse - Are audio forensic procedures reliable?How reliable are audio forensic procedures in the legal system? A student recently asked me that and asked about some of the ins and outs of a career in audio forensics. The student’s specific questions are below and are followed by my answers.

1. How often is speech-based evidence used in court? It’s used very often. Voice identification evidence helps a court to identify people involved in a case and put the puzzle pieces of a case together. Furthermore, voice identification can also sometimes provide substantial enough evidence to cause people to be convicted or released.

Is it a common or rare occurrence? Our business has grown significantly, so I would say that audio forensic procedures in the legal system are common.

2. Is voice identification a lengthy process? It can take up to 4 hours for the average case. This includes 3 types of examination. Audio forensic experts visually examine the sound wave, comparing the evidence and an exemplar (a voice sample of the accused). Next, Audio forensic experts electronically measure the evidence, which is then compared to the exemplar. Finally, and most importantly, audio forensic experts critically listen to compare how the words are spoken and pronounced in the evidence and the exemplar.

3. Are there any factors which can create problems when dealing with a recording? Yes, difference in age between the recording in question and the creation of the exemplar creates problems. People’s voices change with the passing of time. One of the nationally accepted standards for comparing voices is that the voice samples must not be more than six (6) years apart.

4. Is voice identification considered to be reliable within the legal system? YES. However, it’s argued more in some states than others. The forensic expert must carefully examine all scientific evidence and follow procedures. Both law enforcement and defendants seek assistance from audio forensic experts.

For more on Voice Identification, check out Ed Primeau’s latest book, “That’s Not My Voice!” available on Amazon.

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Can’t Convict on Less Than 20 Words

Wednesday, February 22nd, 2012

990276 99980814 - Can’t Convict on Less Than 20 WordsSince 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.

For more on Voice Identification, check out Ed Primeau’s latest book, “That’s Not My Voice!” available on Amazon.

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Original Digital Media Evidence is Mandatory

Saturday, February 5th, 2011

845472 40459282 - Original Digital Media Evidence is MandatoryDigital audio is recorded and stored in electronic equipment. If the audio is needed in court, the original device that created the recording must be identified and kept in a chain of custody. The only exception is when both parties involved in the litigation agree that a copy is sufficient. If there is doubt in the authenticity, the audio expert must refer to the original to support the authentication of the audio evidence.

The reason is that the audio copy has been removed from its original environment and is vulnerable to alteration. In addition, if a computer created the original recording, additional information can be examined by the audio expert such as file creation, last accessed and other computer forensic information that can support the audio evidence authenticity.

If the original audio recording was created in a digital pocket recorder (which many law enforcement officials use) then that original pocket recorder must maintain a chain of custody and become the original evidence. Any external copy created by a number of methods and played outside of the digital pocket recorder is a copy. Unless an audio expert can authenticate the copy (which can be done once the original has been examined) it cannot be used in a court proceeding. If the audio copy has been authenticated by an expert, than it will be easier to play and amplify in the court for a judge and jury.

I have testified in criminal cases for the defense when the client swore under oath that the audio recording had been altered and did not represent the facts as they occurred. Now it’s their word against the other side and when the court has to decide, the prosecution most always, will prevail.

If you have had an experience with audio evidence and would like to share your story, please comment on this post and your story will be heard.

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The Value of an Expert Witness

Friday, October 8th, 2010

4223878274 4715f65f03 b - The Value of an Expert WitnessAn expert witness is a person who by virtue of education, training, skill, or experience, is believed to have expertise and specialized knowledge in a particular subject. His or her expertise is beyond that of the average person, sufficient that others may officially and legally rely upon the witness’s specialized (scientific, technical or other) opinion about their area of expertise. The expert witness will render an opinion (also known as the expert opinion) about the forensic evidence presented.

Expert witnesses help lawyers develop strategies on how the evidence in question should be argued or presented in court. Often time’s audio evidence may not be original or genuine and should be closely examined by the audio forensic expert to authenticate the evidence or strategize with the lawyer on how to write the motion to have the case dismissed or audio evidence removed from the case.

Expert witnesses have a complete understanding of legal proceedings and can be a huge aid to the plaintiff, defendant and courts when a piece of audio evidence is part of the legal case. Defendants who are facing serious charges especially need to seek the guidance and advice of an audio forensic expert. Plaintiffs who want to establish a solid case should seek the help of an audio forensic expert to authenticate their audio evidence prior to entering the court room. Expert witnesses are valuable resources to courts and other legal professionals.

photo credit: DSCN1178 via photopin (license)

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