Sara Wilson Estep began experimenting with EVP (Electronic Voice Phenomena) in 1976 after reading The Handbook of Psi Discoveries by Sheila Ostrander and Lynn Shroeder. She is known as one of the world's leading experts in the field.
Sara's experiments with EVP began on her husband's old reel to reel tape recorder. Over the course of her career she collected thousands of recordings and eventually popularized the classification system originated by Konstantin Raudive. This system is still in use today, as a tool for amateur and professional EVP investigators to specify the quality of their recordings.
Sara went on to found the American Association of Electronic Voice Phenomena in 1982. Until 2000, when she retired, Sara published newsletters, wrote two books, and helped thousands of researchers learn more about EVP and best practices for recording and analyzing their findings.
The AA-EVP is still active today as the Association Trans Communication. You can find their website here. The site is a treasure trove of information. You can listen to recordings Sara and many others have made there. I listened to quite a few of the recordings while researching this post and, I'm amazed at the audio quality of many of them. Given that Sara never used electronic equipment, but tape only recorders in her research, the quality and clarity of many of the samples rivals or surpasses much of what you'll hear today, recorded on electronic equipment.
One of my favorite pages on the site, and the one I personally consider most informative, is titled EVP Online Listening Trials. It contains theoretical explanations of how spirits are able to create EVP and even talks about Agnosia, which is the loss of ability to interpret sensory stimuli, and pareidolia, which I covered briefly in a previous post entitled Am I really seeing that?
Anyone interested in EVP phenomena would do well to include the site, and the work of Sara Estep in their research.