Solving Cases with Voice Stress Analysis (VSA) Technology

From CSI to Lie to Me, people all around the world are becoming entranced with what goes on behind the scenes in computer forensics. Some of the technology that they have in these shows can seem far-fetched or unbelievable, but how far off is Hollywood from the reality of what the investigators can have at their disposal.  Voice Stress Analysis, more commonly known as VSA, is one of those unbelievable technologies that’s within your grasp.

The purpose of this article is to educate you about this forensic tool that can be used to determine whether someone is telling the truth or being deceptive. We live in a time where new technologies and new applications for old ones, are being developed at a faster and faster pace.  Society has always had the same basic needs but they are being met in ever evolving ways.  Just like law enforcement today, people from the earliest times have sought some foolproof method for detecting deception.

History tells of a subterfuge where a donkey was placed inside a dark tent.  The suspect was to enter the tent alone and pull the donkey’s tail. He was told that he would be found guilty if the donkey brayed.  The theory was that a guilty person would not pull the donkey’s tail as this would cause the animal to bray.  Unbeknownst to the suspect, coal soot had been applied to the donkey’s tail.  If the suspect emerged from the tent with clean hands, he was immediately pronounced guilty.

As man’s knowledge and wisdom advanced, more scientific methods were employed.  Astute observers noted that guilty persons, during interrogation, often used certain body language or exhibited signs that could be associated with guilt:   a darting eye, dry mouth, a hand over their mouth when answering, sweating, yawning, or uncontrolled body movements.  Over time, there came breakthroughs in the medical understanding of the observed behavior.

The sciences of psychology and physiology lead to the invention of equipment designed to measure changes caused by how the body reacts to stressful situations.

• In 1895 Cesare Lombroso invented a device called a plethysmograph which was used in lie detection.  It measured changes in blood pressure.
• In 1897 Harold Sticker suggested measuring galvanic skin response (changes in electrical conductivity of the skin, caused by sweating) as a method of detecting deception.
• Vittorio Benussi, in 1914, studied the breathing rates of individuals and how those rates differed depending on whether the person was lying or telling the truth.

As we now know, these psycho-physiological (mind and body) stress reactions can not only be measured, they can be recorded.  The polygraph, the first instrument designed to measure and record those reactions, was developed by John Larson in 1926 and improved by Leonardo Keeler soon after.  It is now a well-established investigative tool that has been the backbone of lie detection.

So, what’s next?

We have already found a way to use the physiological responses of blood pressure, breathing, and the skin to aid in lie detection.  So what came next in biometrics, and is increasingly being used, are the autonomic responses in the vocal chords, the human voice.  In the 1960’s voice stress analysis (VSA) began to be used experimentally by the military.  However, like many technologies, it didn’t start gaining ground until the computer boom in the1980’s, and received harsh bias scrutiny from the competition.

The VSA introduced in the sixty’s was an alternative to the polygraph, and completed in January 1971 by Messer’s Wilson Ford, Alan Bell, and Charles McQuiston (a polygraph examiner) as the first voice stress analyzer.  All were former Army officers.  Their device, called a Psychological Stress Evaluator (PSE), measured stress in the voice and was not a “lie detector” per se.  Unfortunately, the PSE was studied as a ‘lie detector’.  And, many sought still other applications that had nothing to do with its intended use. Therefore, many early studies were flawed in that they failed to evaluate the PSE itself which was created for the sole purpose of measuring stress as it was related to deception.

The Department of Defense Polygraph Institute (DODPI) is the agency charged with evaluating new technologies such as the PSE.  In 2003, the National Academy of Science, following an eighteen month study, exposed a serious lack of studies and credible data when voice stress and other alternatives to polygraph were submitted for review.  The Academy listed “bias, conflict of interest, and unscientific decision making” by DODPI.

The foundation of VSA technology is that a person’s voice emits detectable fluctuation in both AM (amplitude modulation) and FM (frequency modulation) frequencies called microtremors.  When you listen to a person speaking, you hear the AM which rides atop the FM, which is undetectable to the human ear.  Under the stress created from a deceptive response there is a reduction in the FM frequencies causing the microtremors to increase.  It is an involuntary autonomic response detectable with a microphone and a computer running the proper software.  The skilled examiner then analyzes the person’s voice patterns looking for these frequency discrepancies.

VSA works for any language whether the subject is face to face or on the phone.  Drugs, alcohol and medical conditions do not affect the tests.  Voice recordings that are years old can be used to solve cold cases.  And, there are no known countermeasures.  A person can not manipulate his voice frequencies the way he may be able to manipulate blood pressure, breathing, and skin response.  Subjects experience less stress caused by the interrogation as only simple yes and no questions are needed.  And, when face to face, the subject only has a microphone attached.  When compared with a polygraph, the VSA technology is easier to use, faster to administer, less stressful, cheaper., and 98% accurate.

Like the polygraph, VSA is a tool for getting at the truth.  Below is a comparison based on some of the factors Law Enforcement, Attorneys, or Private Investigators have to consider when selecting a method to get to the truth.

VSA technology is currently recognized in 43 states.  Government offices and insurance companies are also using VSA software.  Most people don’t realize that for years, insurance companies have recorded their customers’ conversations when they call to make claims.  Suspicious claims are evaluated utilizing VSA technology.  In a  Department of Defense survey of law enforcement agencies that used the software they found that approximately 85% of the respondents called the technology extremely accurate or very accurate.

Because the only hardware required is a microphone attached to a computer or digital recorder, it can be used in the field.  The U.S. Special Forces used VSA on the battlefield in Iraq and have gone house to house with it.  Unlike polygraph tests, voice stress analysis does not require a sterile environment. VSA examinations provide definitive results, there are no inconclusive results.  Either the subject was being deceptive or they were being truthful.  For this reason you will often read that VSA is a tool used for validating the truth more than for detecting lies.

In addition to its affordability and ease of use, perhaps one of the biggest advantages that VSA offers is that it can be done covertly.  A recording can be made and examined later.  This can be done over the phone or through a hidden microphone. Voice stress analysis has proven that it is the next step in truth verification technology.

For more information on voice stress analysis go to www.forensic-vsa.com or contact the owner of Forensic VSA, Brad Schlerf, an expert in Voice Stress Analysis interviewing.

Forensic-VSA.com has been serving the needs of businesses and law enforcement for over a decade. The owner, retired Police Detective Brad Schlerf, began building & repairing computer systems and developing intelligence gathering software in the 1980’s.  He has developed computer forensic examination protocols for police departments over the last 20 years and has used technologies such as Voice Stress Analysis, computerized facial sketching, audio/video enhancement, and computer and phone forensics.  He was recognized in the book Language of Evil by Robert Beattie because he used his training in body language to break the confession during interviews of Professor Thomas Murray.  He received Advanced Computer Forensic training as a gift from the Wichita BTK Killer investigative team because of his work in forensics.  Brad is recognized as one of the leading investigators utilizing technology, and voice stress analysis techniques in the pursuit for the truth.

Brad Schlerf
Owner, www.forensic-vsa.com
Retired, Hi-Tech Crime Detective
(281) 306-2103
Brad.Schlerf@forensic-vsa.com
Texas Investigator License A16231

Article end-notes:
(AFRL-R 00-102) In fall 2000, Air Force Research Laboratory in Rome, NY, funded by the National Institute of Justice, concluded a three year study of voice stress. Reporting that several features of voice stress are effective for detecting stress when a person is answering questions under stress.  Using audio cassettes of 45 cases AFRL report 100 percent accuracy with two different voice stress analyzers.

CESTARO, V. L. and DOLLINS, A. B. An analysis of voice responses for the detection of deception. June 1994, Report No. DoDPI94-R- 0001. Department of Defense Polygraph Institute, Ft. McClellan, AL 36205. While DoDPI studies failed to use a consequence of stress in their evaluation, Dr. Cestaro did report that the Voice Stress Analyzer does work according to the manufacturer’s theory of operation and more importantly, “these data indicate there may be a systematic and predictable relationship between voice patterns and stress related to deception”.

The 2000 Air Force Research Laboratory report combined with the 1995 DoDPI report, the Department of Defense Polygraph Institute and report No. DoDPI95-R-0002., serves as proof positive that voice stress analysis works.

US Dept. of Justice NCJ 196934 The theory behind the VSA is that it detects physiological micro tremor associated with muscles in the voice mechanism. The results of the laboratory test show that the VSA functioned electrically according to frequency modulation detection theory. The VSA instrument was shown to detect discrete changes in speech fundamental frequency using laboratory instruments to simulate voice micro tremor, confirming the underlying theory of operation.