As the EVP research movement grew, the American Association of Electronic Voice Phenomena, founded in 1972 by EVP researcher Sarah Estep. It later became known as the Association Transcommunication (ATransC) and survives to this day.

This was followed by research associations forming all around the world, starting with des Vereins für Transkommunikations-Forschung (German Association for Transcommunication Research), which was founded in Germany in 1975.

Estep began her research into EVP using a reel-to-reel tape recorder in 1976 after reading about the work of Friedrich Jürgenson and Konstantin Raudive. She went on to become a leading researcher in her field, making hundreds, if not thousands, of recordings of voice messages, some of which she identified as deceased friends and relatives and even intelligences of extraterrestrial origin.

Perhaps Estep's best-known legacy is her popularization of the EVP classification system. It was similar to a previous system of classification proposed by Raudive. Estep's system used the...