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.
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.
Digital 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.
An 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.
