Voice Stress Analysis

Jan 23, 2019


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What is Voice Stress Analysis?

It is a pseudo scientific technology used to measure deception from the voice of a person being tested. The person speaks and a microphone records their voice frequencies.

Benefits of the Voice Stress Analysis are:

  • That it is more hygienic (No Electrodes and or Sensors are attached to the subject being tested);
  • That it is more subject friendly; and
  • That it is less intimidating. (a more relaxed environment due to the subject speaking into a microphone which is a lot less daunting).


How does a Voice Stress Analysis work?

The objective of the Voice Stress Analysis similar to a Polygraph test; it is to assess whether the subject’s version of an event is a true reflection of the facts.

  1. The subject being tested is required to complete a consent form giving permission for the test and stipulates who may view the results.


  1. The Voice Stress Analyst must explain the reason for the test together with the process to be followed.


  1. It is imperative that the subject understands which questions will be asked and what the relation is to the incident.


  1. The subject is asked a range of questions that include control questions.


  1. The subject’s natural body behaviour is measured without any physical attachments unlike a polygraph test.


  1. Only a qualified analyst may conduct a Voice Stress Analysis.

The natural behaviour of a person, who is experiencing stress, is fight, flight or freeze.  This causes their throat muscles to tighten which has an effect on their vocal cords and is picked up in a person’s voice.

The result to each question asked by the examiner is available immediately.  This may lead the examiner to ask more direct question pertaining to a specific object, person and or situation.

The results from a Voice Stress Analysis in conjunction with the circumstantial evidence are used to identify the merits of an incident.


Why would you consider a Voice Stress Analysis to be conducted?

A Voice Stress Analysis Test without any reason or circumstance will be ineffective.

For example: The Director of Company XYZ thinks one or more of his employees are embezzling company funds. He wants to test all of his employees.

There must be a reason for the test.

For example: The Director of Company XYZ thinks one or more of his employees are embezzling company funds due to sales targets being reached but the Company financial statements does not reflect the profits..

Conducting a random Voice Stress Analysis Test will scare off loyal employees who are innocent.

Be sure to take the following circumstances into account:

  • Incorrect invoicing;
  • Incorrect or confusing product labels or codes;
  • Company expenses;
  • Access to accounts;
  • Authorisation of payments; and
  • Systems errors.


Formulating of Questions to be asked

The outcome of the voice Stress Analysis needs to be carefully considered prior conducting the test. Therefore as with a polygraph the, the questions have to be carefully formulated and have to be event, incident and or subject specific.

It is important to remember that the questions need to be Yes/No questions.

Control Questions will be asked as well as Questions relevant to the event, incident and or subject:

  • Have you ever sent an incorrect invoice to a customer;
  • Have you ever informed your superior of amended documentation;
  • Do you find the product labels or codes confusing;
  • Do you have access to the company accounting system;
  • Can you authorise payments and who else is authorised to release payments;
  • Have you ever falsified a signature or authorisation for a payment;
  • Do you always follow the procedures for authorisation of payments;
  • Do you think any of the procedures are badly written or implemented; and
  • Have you ever seen anyone falsifying authorisation for payments?


The Analysis

There are 4 phases of analysis:

1st Phase       – Calibration of stress levels during the subject’s statement and forming a stress “base line”. This indicates the subject’s natural level of stress before the monitoring of voice patterns;

2nd Phase      – Pre Examination of voice patterns;

3rd Phase       – Examination and analysis of statements and cross questioning; and

4th Phase       – Direct Questions with Yes and No answers.


Result Specifications

The results indicate which questions were asked, and if the answers provide isa true reflection of events based on the reaction of a subjects voice.

Reactions can be as follows:

  • Deception             – Subject is NOT telling the truth;
  • No deception             – Subject IS telling the truth;
  • Subject not sure -Subject is confused;
  • Extreme Stress             -Subjects reaction to direct questions indicate higher stress levels than the average levels monitored during the calibration phase. Normally this happens when the subject is anticipating the next question due to guilt or fear. This can also occur if a questions peaks the subjects stress levels higher than the subjects normal stress levels. Extreme Stress does not indicate deception, unless the word “deception” accompanies the words “Extreme Stress”.
  • Voice Manipulation – Subject is trying to sound convincing; and
  • Cognitive stress – Holding back information for the purpose of “covering up” for someone.


Is it possible to cheat?

No, as the test measured notes in your voice and no physical factors like heart rate or movement. It would be extremely difficult to try and control your voice while not sounding like you are trying to do just that.

Can the results be faulty?

Yes, it is possible as with the Polygraph tests. The formulation of questions may be incorrect and or the examiner can read the results incorrectly. (This is unlikely but human).

What can the Voice Stress Analysis be used for?

Similar to a Polygraph Test (refer to our previous post.) It can be used for a range of things including the following:

  • As part of a recruitment process for new applicants (It is recommended when the position is one that requires trust);
  • To check an employee’s version of an incident which caused harm to the organisation (Use caution as innocent employees may resign);
  • Drug and alcohol usage;
  • Theft;
  • Fraud; and
  • Domestic affairs.


Why do people lie and why do they fight, flight or freeze when caught? Read our next post to find out more.


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