Voice Identification Line Up

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 as it was 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 is to keep it simple.  Judges like an uncomplicated 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.  

Clarification for Authentication of Audio Recordings

The following article was written to help the legal community better understand the audio clarification process. The descriptions it includes will also help a lay person better understand the value of audio clarification.

All digital and analogue recordings have a noise floor. The term “noise floor” originated when manufacturers of analogue audio recorders referred to the extraneous noise that their machines created in addition to the desired recorded audio signals.

Often, a background noise constitutes most of the audio recording and covers a portion of speech that needs to be audible in order to determine a series of events pertinent to the case. Noises like the humming of a fan, air conditioning, heating systems, wind, and other unwanted sounds contribute to the audio recording noise floor. These noises can often be removed by the audio forensic expert (who is also known as the examiner) to help determine facts about the series of recorded events.

The extraneous sounds of background noise and noise floor can consist of a heating or air conditioning fan running, refrigerator motor, window fan, clock, fluorescent lighting, wind, rain, the running engine of a car, and even radio or television. All these sounds contribute to the background noise and noise floor of a recording and aid the forensic examiner in authenticating a recording. However, although these sounds can authenticate the environment of an alleged crime, this background noise can interfere with the forensic examination. It is appropriate and part of the forensic examiners job to remove these background sounds in order to authenticate or clarify an exhibit of audio recorded evidence.

Some of the recordings experts are asked to authenticate are confession recordings created by law enforcement agencies. Defendants exclaim, “That is not what I said, they edited it” or “There is more I said that has been edited out of the recording”. Due process entitles both parties in litigation to examine any evidence presented in their case. However, original recordings are not always available for examination. How do you as a law enforcement official feel about the absence of original recordings?

I have worked on cases where missing “original evidence” was considered spoliation of evidence. Personally, I believe that the circumstances of each case should be considered by the forensic examiner before any decision has been made by either party.

If there are noticeable questionable characteristics that the forensic examiner observes regarding the audio evidence, then the expert must notify the officials in charge of the findings during the preliminary examination phase of the forensic investigation. Original recordings are required for litigation cases. If they are not produced, a motion to suppress the evidence should be filed.