Any analytical technique implemented to determine whether changes in the vocal signal are indicative of changing levels of stress. Most techniques assess the frequency or amplitude modulation of the vocal signal in one or more frequency bandwidths. Emphasis is often placed on modulation in the 8-10 Hz frequency bandwidth, otherwise known as microtremors. Numerous voice stress analysis devices have been introduced since the first was made available in 1971. All purport the ability to detect deception. Today, this genre of credibility assessment devices enjoys wide distribution, possibly due to their low cost and brief training requirements relative to the polygraph. However, no independent scientific assessment has validated the use of voice stress analysis for credibility assessment. Because of this, these devices are prohibited from being use by the US Department of Defense. Brand names include Computer Voice Stress Analyzer (CVSA), Lantern, Psychological Stress Evaluator (PSE), TiPi, VSA Mark, Victor, and Layered Voice Analysis (LVA).