Many academics get extremely caught up in their work and Dr Konstantīns Raudive was no exception.
Holed up in a university laboratory, he was feverishly moving a reel-to-reel tape back and forth on their loops. He would experiment with the insertion of various radio frequencies. Then he would listen to the white noise. All of this over and over again for six years.
It was 1965 and Raudive had had to flee from his native Latvia. His country had been invaded by the Soviet Union and, as a practicing Catholic, he didn't fancy his chances there much.
An intelligent man, and a qualified psychologist, Raudive soon found work in Sweden. The University of Uppsala appears to have been very indulgent in allowing him lab time to pursue his interest in parapsychology.
At first, it was merely an interest. He had read a book by Friedrich Jürgenson entitled Rosterna fran Rymden ('Voices from Space'), which had fascinated him.
Amongst his many other jobs and hobbies, Jürgenson was a recording artist and a documentary film-maker. As part of a project, he had set up a tape recorder to capture the sound of bird song. It was a peaceful location, just himself and the avian chorus all about him.
So it came as a bit of a surprise when he played the tape back and heard human voices on it.
By attempting to recreate the same conditions in various locations, Jürgenson was able to capture many more voices just like them. However, he didn't assign a paranormal explanation to the phenomenon until he recorded one in the house in which he grew up.
It was his mother's voice and she had been dead for years.
What Raudive did, after meeting with Jürgenson, was to try and repeat this phenomenon under test conditions in a laboratory. He too was reluctant to attribute it to ghosts, until he also heard a voice that he recognized.
Six years later, Raudive had over 100,000 snippets of what later would be called EVP recordings. They had been heard simultaneously by various people in the group (there were eventually over 400 people working on the project).
By documenting the frequencies in such a way, the academic world, then the popular press, were alerted to the field.
Using Raudive's methodology, Professor Imants Barušs, at King's College University of Ontario, was able to reproduce these voices in 1997. His experiments were described in the October 2001 edition of the Journal of Scientific Exploration, where they were open to peer review.
Barušs established that, while he could replicate what Raudive had done and heard, he found nothing that could be 'attributable to discarnate beings'.