Electric Voice Phenomena
Electronic Voice Phenomena is the interpretation of sounds on electronic recordings as spirit voices. Scientists consider EVP a form of auditory pareidolia, the brain finding patterns where none exist. Nevertheless they are a major part of paranormal culture, with many claimed examples and explanations for their appearance. An early proponent of the idea that spirits could be recorded by sensitive equipment was - perhaps surprisingly - Thomas Edison. He considered this process much more likely to result in effective communication with the spirit world than devices such as ouija boards. There’s no evidence that he ever tried to build or use such a device for this purpose. After this mediums began to consider the use of the technology to communicate with the dead. As the 20th Century progressed spiritualism declined, but people continued to use modern digital technology to communicate with spirits.
Scientific explanations for the supposed spirit voices can include interference caused by many external factors, faulty grounding or other equipment issues, or cross-modulation - when two or more frequencies interact with each other and cause changes to the waveforms, sometimes adding spurious signals at other frequencies. Some researchers, such as ex-EdSkeptics speaker Chris French, have suggested that the raising of the noise floor that is typically carried out when making these recordings could lead to speech-like sounds when the resulting white noise is filtered. The signals generated by falling meteors have also been mooted as a possible solution.
There are many other possible explanations on top of pareidolia for the appearance of EVP in recordings. Many scientists have commented on the possibility of RF interference cropping up, leading to noises that could be interpreted in certain ways. To their credit many paranormal researchers have conducted research in RF-screened environments and using equipment screened against RF-leakage. Despite this most scientists would point to other natural and technical explanations before concluding that the appearance of voices was due to any kind of paranormal phenomena. Picture credit: Omegatron