Voice Stress Analysis

Voice Stress Analysis (VSA) technology is said to record 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 may be dire for the subject being 'tested'.^[1]
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'. However, it is not possible to cleanly separate the excitation signal into components due to emotion and those due to deception. Thus no DOD technology can detect a lie or truth unequivocally, but only whether a speaker is experiencing stress. For example, a suspect under questioning would also display natural stress even if he were not guilty.
The technique's accuracy remains debated. There are no independent research studies that support the use of VSA as a reliable lie detection technology, whilst there are numerous studies that dispute its reliability.^[2][3]
In civil court testimony, the CVSA founder, Mr. Charles Humble, testified that "NITV acknowledges that the CVSA is not capable of lie detection and specifically cautions its users regarding proper use of the device."^{[citation needed]}
Air Force Research Laboratory (Haddad et al.) conducted validation studies into VSA and concluded that mainstream VSA (Diogenes and CVSA) as well as polygraph tests are useful in helping trained operators in obtaining confessions by convincing the subject that they cannot deceive the device. As such, it is considered a useful interrogation tool.<sup>[citation needed]

http://en.wikipedia.org/wiki/Voice_stress_analysis</sup>