The PSE, or Psychological Stress Evaluator, is a voice stress analyzer that was designed to be used in the same manner as a polygraph for one-on-one testing for the detection of deception. The PSE detects, measures and graphically displays certain stress-related components of the human voice.

Superimposed on the audible voice are inaudible frequency modulations. The FM quality of the voice is susceptible to the amount of stress that one may be under when speaking. To the human ear, a person may sound perfectly normal, free of tremors or "guilt-revealing" sound variations. The PSE senses the difference and records the change in the inaudible FM qualities of the voice on a chart. When the chart is interpreted by an experienced examiner, it reveals the key stress areas of the person being questioned.

When one speaks, the voice has two modulations; audible and inaudible. The audible portion is what we hear. The inaudible modulation comes from involuntary areas, those not totally controlled by the brain or thought processes. Internal stress is reflected in the inaudible variations of the voice. These differences cannot be heard, but they can be detected and recorded by the PSE.

The key to successful use of the PSE is in the preparation of selected questions keyed to the individual and structured to reveal normal or truthful answers and answers that are false. Once the personal pattern has been established, any evasive or false answers reveal stress. If a person is not telling the truth, analysis of their voice patterns will reveal it.

The PSE has great advantages over similar instrumentation in that it does not have to be used at the time of the interview or interrogation. A tape recorder is used to make a permanent record of the interview and this tape can later be fed into the PSE where the voice reactions are recorded on a chart.

Questions containing either yes or no answers, or entire conversations can be analyzed with the PSE. The PSE is an investigative tool that has proven itself time and again in the field of civil and criminal investigations.