"The term Instrumental Trans-Communication (ITC) was coined by Ernst Senkowski in the 1970s to refer more generally to communication through any sort of electronic device such as tape recorders, fax machines, television sets or computers between spirits or other discarnate entities and the living. One particularly famous claimed incidence of ITC occurred when the image of EVP enthusiast Friedrich Jürgenson (whose funeral was held that day) was said to have appeared on a television in the home of a colleague, which had been purposefully tuned to a vacant channel. ITC enthusiasts also look at TV and video camera feedback loop of the Droste effect.
In 1979, parapsychologist D. Scott Rogo described an alleged paranormal phenomenon in which people report that they receive simple, brief, and usually single-occurrence telephone calls from spirits of deceased relatives, friends, or strangers. 
In 1997, Imants Barušs, of the Department of Psychology at the University of Western Ontario, conducted a series of experiments using the methods of EVP investigator Konstantin Raudive, and the work of "instrumental transcommunication researcher" Mark Macy, as a guide. A radio was tuned to an empty frequency, and over 81 sessions a total of 60 hours and 11 minutes of recordings were collected. During recordings, a person either sat in silence or attempted to make verbal contact with potential sources of EVP. Barušs stated that he did record several events that sounded like voices, but they were too few and too random to represent viable data and too open to interpretation to be described definitively as EVP. He concluded: "While we did replicate EVP in the weak sense of finding voices on audio tapes, none of the phenomena found in our study was clearly anomalous, let alone attributable to discarnate beings. Hence we have failed to replicate EVP in the strong sense." The findings were published in the Journal of Scientific Exploration in 2001, and include a literature review.
In 2005, the Journal of the Society for Psychical Research published a report by paranormal investigator Alexander MacRae. MacRae conducted recording sessions using a device of his own design that generated EVP. In an attempt to demonstrate that different individuals would interpret EVP in the recordings the same way, MacRae asked seven people to compare some selections to a list of five phrases he provided, and to choose the best match. MacRae said the results of the listening panels indicated that the selections were of paranormal origin.
Portable digital voice recorders are currently the technology of choice for EVP investigators. Since these devices are very susceptible to Radio Frequency (RF) contamination, EVP enthusiasts sometimes try to record EVP in RF- and sound-screened rooms. Nevertheless, in order to record EVP there has to be noise in the audio circuits of the device used to produce the EVP. For this reason, those who attempt to record EVP often use two recorders that have differing quality audio circuitry and rely on noise heard from the poorer quality instrument to generate EVP.
Some EVP enthusiasts describe hearing the words in EVP as an ability, much like learning a new language. Skeptics say that the claimed instances are all either hoaxes or misinterpretations of natural phenomena. EVP and ITC are seldom researched within the scientific community and, as ideas, are generally derided by scientists when asked.
Explanations and origins
Most explanations of EVP can be categorised as either paranormal, explaining the source of the voice, or non-paranormal. Explanations of the latter kind usually posit (except in the case of hoaxes) that there is actually no 'voice' at all, merely the illusion of a voice due to various effects.
A number of paranormal explanations have been suggested for the origin of EVP. Explanations include living humans imprinting thoughts directly on an electronic medium through psychokinesis and communication by discarnate entities such as spirits, nature energies, beings from other dimensions, or extraterrestrials.
There are a number of simple scientific explanations that can account for why some listeners to the static on audio devices may believe they hear voices, including radio interference and the tendency of the human brain to recognize patterns in random stimuli. Some recordings may be hoaxes created by frauds or pranksters.
Psychology and Perception
Auditory pareidolia is a situation created when the brain incorrectly interprets random patterns as being familiar patterns. In the case of EVP it could result in an observer interpreting random noise on an audio recording as being the familiar sound of a human voice. The propensity for an apparent voice heard in white noise recordings to be in a language understood well by those researching it, rather than in an unfamiliar language, has been cited as evidence of this, and a broad class of phenomena referred to by author Joe Banks as Rorschach Audio has been described as a global explanation for all manifestations of EVP.
Skeptics such as David Federlein, Chris French, Terrence Hines and Michael Shermer say that EVP are usually recorded by raising the "noise floor" - the electrical noise created by all electrical devices - in order to create white noise. When this noise is filtered, it can be made to produce noises which sound like speech. Federlein says that this is no different from using a wah pedal on a guitar, which is a focused sweep filter which moves around the spectrum and creates open vowel sounds. This, according to Federlein, sounds exactly like some EVP. This, in combination with such things as cross modulation of radio stations or faulty ground loops can cause the impression of paranormal voices. The human brain evolved to recognize patterns, and if a person listens to enough noise the brain will detect words, even when there is no intelligent source for them. Expectation also plays an important part in making people believe they are hearing voices in random noise.
Apophenia is related to, but distinct from pareidolia. Apophenia is defined as "the spontaneous finding of connections or meaning in things which are random, unconnected or meaningless", and has been put forward as a possible explanation.
Interference, for example, is seen in certain EVP recordings, especially those recorded on devices which contain RLC circuitry. These cases represent radio signals of voices or other sounds from broadcast sources. Interference from CB Radio transmissions and wireless baby monitors, or anomalies generated though cross modulation from other electronic devices, are all documented phenomena. It is even possible for circuits to resonate without any internal power source by means of radio reception.
Capture errors are anomalies created by the method used to capture audio signals, such as noise generated through the over-amplification of a signal at the point of recording.
Artifacts created during attempts to boost the clarity of an existing recording might explain some EVP. Methods include re-sampling, frequency isolation, and noise reduction or enhancement, which can cause recordings to take on qualities significantly different from those that were present in the original recording.
The very first EVP recordings may have originated from the use of tape recording equipment with poorly aligned erasure and recording heads, resulting in the incomplete erasure of previous audio recordings on the tape. This could allow a small percentage of previous content to be superimposed or mixed into a new 'silent' recording.
Sporadic meteors and meteor showers
For all radio transmissions above 30MHz (which are not reflected by the ionosphere) there is a possibility of meteor reflection of the radio signal. Meteors leave a trail of ionised particles and electrons as they pass through the upper atmosphere (a process called ablation) which reflect transmission radio waves which would usually flow into space. These reflected waves are from transmitters which are below the horizon of the received meteor reflection. In Europe this means the brief scattered wave may carry a foreign voice which can interfere with radio receivers. Meteor reflected radio waves last between 0.05 seconds and 1 second, depending on the size of the meteor.
The Association TransCommunication (ATransC), formerly the American Association of Electronic Voice Phenomena (AA-EVP), averages around 500 members in 47 USA states and 22 countries including the USA (current: 2007)." and the International Ghost Hunters Society conduct ongoing investigations of EVP and ITC including collecting examples of purported EVP available over the internet.. The Rorschach Audio Project, initiated by sound artist Joe Banks,  which presents EVP as a product of radio interference combined with auditory pareidolia and the Interdisciplinary Laboratory for Biopsychocybernetics Research, a non-profit organization dedicated studying anomalous psi phenomena related to neurophysiological conditions. According to the AA-EVP, it is "the only organized group of researchers we know of specializing in the study of ITC.".
Spiritualists, as well as others who believe in Survivalism, have an ongoing interest in EVP. Many Spiritualists believe that communication with the dead is a scientifically proven fact, and experiment with a variety of techniques for spirit communication which they believe provide evidence of the continuation of life. According to the National Spiritualist Association of Churches, "An important modern day development in mediumship is spirit communications via an electronic device. This is most commonly known as Electronic Voice Phenomena (EVP)". An informal survey by the organization's Department Of Phenomenal Evidence cites that 1/3 of churches conduct sessions in which participants seek to communicate with spirit entities using EVP.
The James Randi Educational Foundation offers a million dollars for proof that any phenomena, including EVP, are caused paranormally. The prize remains uncollected."