Archive for the ‘Exemplar’ Category

Voice Identification: Characteristics of an Unknown Voice

Monday, January 12th, 2015

voice identificationOne of the most important elements of Voice Identification is the ability to recognize the characteristics of the human voice. There are many elements to distinguish these characteristics, some audial, some visual.

Think about when you have your back to a person who enters the room and says hello. If it is your child, spouse or co-worker, I bet you recognize them immediately because you are familiar with their voice. This is the starting point for voice identification; becoming familiar with the characteristics of the unknown voice.

I began editing spoken word on reel-to-reel tape with razor blades and splicing tape. I had to learn to visualize the words in my mind’s eye in order to cut the tape in the right place. Today, we have software programs that display the waveform and sound spectrum of the spoken words, which make the editing process more accommodating. The editor can see the
way the words look on the computer screen while deciding where to make the edit and connect the sentences, removing the stutters, coughs, gaps and mistakes.

During the editing process, you will learn to listen for voice characteristics almost subconsciously. These characteristics include the way the words are spoken, the word pronunciations, vowel and consonant pronunciations, the recording noise floor (unwanted background noise), the way the words flow together, and significant patterns of speech you may detect, like accent, dialect and impediments, nasal cavity resonance, voice tone and inflection and speech pacing.

Pay attention to both differences and similarities from recording to recording, and take notes on your observations building a speech database for when writing the report.

Exemplars are defined as expert supervised audio recordings of predetermined spoken word samples for the purpose of voice identification comparison. During the exemplar creation process it is important to coach the person (subject) speaking for the recording into the same level of energy as the evidence recording of the unknown voice. Listen to the energy and attitude of the voice you are examining (evidence or unknown recording). Do you hear a mood or psychological characteristic in the voice?

In some bomb threat recordings I have examined, the speakers have an angry, sad or depressed attitude in their voice while speaking the recorded words. It is important to note that at the time of creating an exemplar, the subject is often not in the same psychological state as the individual in the unknown recording. While making the exemplar, do your best to coach the person (suspect) to speak with the same energy as the voice on the evidence recording.

Your critical listening ear will help you complete this process to the best of your (and their) ability. You have to listen critically beyond the subject’s current mood, because it is often difficult to coach them into the mood of the person on the evidence recording. Listen for specific speech characteristics in the exemplar and evidence recordings. What do you notice about the unknown voice that is characteristic of the known voice?

To practice, spend some time listening to spoken word recordings. These can be in the form of talk radio, podcasts and audio books. Write down speaking characteristics of the voice recordings like this:

• English accent

• Southern accent

• Consistent sibilant “s”

• Consistent long “a”

• Medium pitch, low pitch, high pitch

• Emphasis on “al” as in “halp” instead of “help”

• Does the subject have a characteristic rhythm to his speech or a pattern of delivering words and pausing?

Listen to several spoken word recordings and make a list of speech characteristics. Take notes on your observations.

Only through practice and experience will you become familiar with voice identification. When creating a new audio comp or assembly file in Sony Sound Forge or Adobe Audition, you will be able to listen to the speech sections that you are comparing repeatedly and with easy access. Back-to-back critical listening is an extremely important tool for voice identification. It is the best way to develop your critical listening skills and begin to recognize the different speaking characteristics of each voice examined. The familiar and unfamiliar speaking samples can be identified and characteristics can be easily noted.

Learn more about Voice Identification and Critical Listening in Forensic Expert Ed Primeau’s new book, That’s Not My Voice! available now on Amazon.

Audio from Video Evidence Offers Additional Clues

Friday, September 14th, 2012

Aaudio from video editingudio and video forensics go hand in hand in a lot of today’s litigations. As an audio and video forensic expert, I work for both the prosecution as well as the defense. Lately I’ve been working more for the prosecution and I am seeing audio and video evidence being used more often to prosecute cases than ever before. Traditionally defendants would contact me because they believed the police had altered audio and video evidence that was being used in the prosecution’s case. As an expert of almost 29 years, I think about that when I’m contacted by these defendants and wonder why a police officer would risk his reputation, his retirement and his entire career by altering evidence in order to convict. But it’s still my job to authenticate and to investigate when I am asked.

Recently I worked on a case for a police department where there were questions about who said what on a dashcam video. This is where the audio and video forensics intersect in litigation. The dashcam was static and nothing could be seen regarding the series of events as they occurred. However, the microphone in the car and an officer’s microphone were on, allowing the video to record the audio of the situation. What was in question was who said what in the recording. I was able to get samples – or exemplars – of the voices of the people that were at the scene of the crime and compare them to the voices that were recorded on the dashcam video. I had my assistant create a transcription and we started with “voice one, voice two, voice three” because the voices were significantly different (which isn’t always the case). They were different enough that the listener could determine three separate distinct voices. These differences were also an advantage because the voices were all male, which sometimes makes it difficult to differentiate between the parties being recorded. By creating a transcript and determining through voice identification investigation, I was able to recreate what the camera did not see through an audio forensic process.

So when prosecuting a case, it’s important to consider both audio and video aspects of the investigation even if the video may seem hopeless. When you work with an audio and video expert, that expert can give you some advice and ideas of clues that could be picked up in the evidence to help your case. Even if the clues start out small, they may turn into evidence that can be used to help prosecute. The clues will at least bring some more truth into the courtroom, which is the job of the audio and video forensic expert.

photo credit: Clip Show via photopin (license)

The Voice Identification Lineup

Tuesday, May 31st, 2011

voice identificationRecently 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.

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


photo credit: office phone via photopin (license)

Creating an Audio Exemplar for Voice Identification

Tuesday, May 17th, 2011

Voice Identification 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.

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

photo credit: Stop via photopin (license)

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