voice-stress analyzer

Voice stress analysis

Voice Stress Analysis (VSA) is a lie detection technology- and uniquely deployed as such- which is newer than the polygraph, but still controversial.

VSA technology records psychophysiological stress responses that are present in human voice, when a person suffers psychological stress in response to a stimulus (question) and where the consequences of lying may be dire for the subject being 'tested'.

In the Detection Of Deception (DOD) scenario, the voice-stress produced in response to a Relevant Question ("did you do it?") is referred to as psychological stress or 'deceptive stress'. No DOD technology can detect a lies or truth unequivocally. It is the fear of being exposed as lying to the question being posed that produces the 'high stress' voice signature, aka voice graph or voice tracing.

The technique's accuracy remains debated by polygraph-industry initiated research. There are independent research studies that support the use of VSA as a reliable lie detection technology, whilst there are other studies that dispute its reliability.

For example, a 2005 study found the TrusterPro LVA system to be invalid for detection of guilty knowledge. Research commissioned by the Department of Justice and conducted by AFRL (Air Force Rome Labs), as well as several other researchers, also suggested less accuracy rates for the same system, marketed in the US under a different name ("Vericator").

The skill and experience of the VSA Examiner is of utmost importance.

LVA - Layered Voice Analysis technology- known as LVA or VRA - is finding use as a screening tool in the UK, in which recipients of jobless benefits are faced with the 'threat only' of a test, and would consequently face more scrutiny if they "failed".

The LVA test itself has accuracy levels less than chance (50%) but the mere threat is used in this instance.

LVA trials conducted by private Polygraph & VSA Instructor/Examiners in South Africa produced reliability levels of 20%. Consequently LVA is a non qualifying technology for membership to the Polygraph And Voice Stress Association of SA. (PAVSA).

VSA is distinctly different from Layered Voice Analysis (LVA). LVA is used to measure many different components of the voice, but is not reliable in the detection of 'deceptive stress'. LVA measures a wide range of emotions, including excitement, confusion, attention and more. LVA is available in many different forms of products, ranging from server based intelligence use systems, to hand-held devices and standard PC software. The Sense Technology , the consumer version of the LVA technology, is available in different products and produces non-useful readings such as 'love' and 'Embarrassment' (not relevant in DOD applications).

The main difference in the method of operation between LVA and VSA is based on the analyzed frequencies ranges: while VSA focuses on the 8-14 Hz range (which is picked up by specialised microphones), LVA uses a wider spectrum range to extract information that is amusing but not particularly relevant to DOD. .

Principle and origins

VSA is based on the subsonic components of human voice not audible to observers, now known as the Lippold Tremor. In 1957, Olaf Lippold discovered this physiological tremor in the human voice in the 8-12 Hz range. Lippold, Redfearn and Vuco began exploring the correlation between muscle activity and stress, and found that when the fight or flight response presents in a person, one of the psycho-physiological responses that manifest, is the involuntary tensing of the 'soft' striated muscles, particularly, the laryngeal muscles. Under normal circumstances, the laryngeal muscle is relaxed, producing recorded voice at approximately 12Hz. Under stress however, the tensed laryngeal muscle produces voice significantly lower in pitch.

The original VSA technology was devised by three former US Army personnel. The three, Bell, McQuiston & Ford, developed the PSE 1, an analogue machine. The three, under Dektor Counterintelligence and Security, Inc., manufactured the PSE 1000 and later the PSE 2000. The first supplier of VSA technology was Dektor Counterintelligence and Security Inc. Dektor manufactured the PSE 1000, an analogue machine, that was later replaced by the PSE 2000.

The National Institute Of Truth Verification (NITV, West Palm Beach) then produced and marketed a digital application based on the McQuiston-Ford algorithm in April, 1997.f> In the past 10 years VSA has been used primarily in digital applications: Digital Voice Stress Analysis (D-VSA). The primary suppliers are NITV-CVSA; Dektor-PSE5128, Diogenes-Lantern and Baker-FVSA.

The primary use of VSA is in the arena of 'Detection Of Deception'. As with the polygraph, VSA technology is inert. It has no artificial intelligence component. It can be said that both technologies are equally reliable in determining a person's truthfulness under similar circumstances. Both technologies record data that they were designed to do. It is the use of that data as a means for lie detection that remains controversial.


The purpose of a VSA examination is to determine the truthfulness of responses made by an examinee regarding the subject under investigation. Determinations are made by analyzing and scoring the voice-grams produced by the examinee. Traditional analysis of voice grams was achieved by allocating "percentages of stress" (% ) according to the patterns so produced.

High levels of (deceptive) stress indicate that the examinee is deceptive as is the case with polygraph. In respect of VSA, squared voice grams indicates higher stress, whilst 'wave form' or 'domed' signatures indicate less stress.

Questions may be posed to elicit simple "yes" or "no" answers, but can be posed to produce a narrative response. Questions are formulated for each individual being examined to compare situational stress signatures with Control Question and Relevant Question signatures, in order to identify (deceptive) 'stress signatures'.

VSA technology together with validated testing protocols, is designed to protect the innocent and avoid 'false positive' results. VSA is designed to assist any investigation by establishing the veracity of a subject's verbal responses.

Devices used to analyze voice stress are usually used in the presence of the individual under investigation; however, they can also be used without his or her knowledge. Since all that is needed is a voice, a wireless microphone or a tape recording can provide the necessary input signal.

Traditional VSA utilizes the McQuiston-Ford algorithm and this is the technology developed in the USA for the US Defence Agencies and is used by US Law Enforcement agencies.

There are no known physical countermeasures for VSA. Conversely, the simple use of a 'tack' placed under the tongue of the examinee, to be used as a countermeasure, can reduce the accuracy of polygraph results from 98% to 26%.

Use In law enforcement

A great deal of voice stress testing (VSA) has been conducted. In the United States, most states do not regulate the private use of these devices. However, the CIA and FBI both use VSA at times, in their own investigations. The technology is currently recognized in 43 states.

Many intelligence agencies as well as private forensic psychophysiologists worldwide utilise VSA in preference to polygraph technology.

Methodology and accuracy

The McQuiston-Ford algorithm used for Voice Stress Analysis is reliably accurate. The recorded "micro tremors" in a persons voice are converted via the algorithm into a scorable voice gram. The discrepancy in researched accuracy may result from incorrectly trained or non-trained persons utilizing the technology incorrectly. This is evident by some Polygraphists trying to "test" VSA technology without having received accredited training in the use thereof.

Polygraph-only associations have disputed the accuracy of VSA, although many accredited polygraphists have trained in the use of VSA and use VSA to good effect. The traditional analysis and scoring of voice-grams by means of assigning 'percentages' is time consuming.

In 2002, Clifton Coetzee (Polygraph & VSA Instructor) devised a scoring method for voice grams incorporating the 'UTAH 7 Point' scoring system, as used by modern day polygraphists. Reactive or Responsive patterns are assigned a weighting of +3 to -3.

The use of CQT testing protocols developed by John Reid and Cleve Backster are used for greater reliability of VSA results. It is important that VSA examiners be skilled in the use of enforced, timed pauses between stimulus (question) and response (answer). As in the polygraph situation, the fight or flight response has onset and conclusion delays, which must be considered by examiners to achieve reliable results.

The American Polygraph Association's website lists conclusions from multiple studies into the accuracy of voice stress analysis as a means of detecting the subject's truthfulness. All cast doubt on the validity of the results of such tests; many describe the results as no better than chance.


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