The Raudive Scale was soon replaced by a classification system that was clearer and took into account filtering and amplification where needed. The first iteration of this system was first popularized in Sarah Estep's 1988 book, 'Voices of Eternity.' The scale became a global standard for EVP classification.


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The Estep System


Class A
Voices are loud and clear, they can be duplicated onto other tapes. Can be heard without headphones.


Class B
Voices aren't as loud and clear, and can often be heard without headphones.


Class C
Voices are faint or whispery. Headphones must be worn to hear them, and rarely can all the words...