Defining 'White Noise'
The term 'white noise' actually has different meanings dependent upon the context in which it is used. In the context of this article we are referring to audio signals that produce white noise. Primarily radio signals / frequencies that emit that hallmark static hisses, crackles and pops that we normally associate with 'dead-air' and static.
White noise is a collage of all sound frequencies that the human ear and brain is able to hear and perceive.
White Noise also includes sub-audible sounds and vibrations, those outside our range of hearing - like a dog whistle.
Sound is measured in 'hertz' and 'mega-hertz' - the average Human range is20 to 20,000 Hz, although some rare individuals are able to perceive slightly above that range. White noise generally goes beyond the 20,000 Hz range and every degree within that range represents a different tone.
The sound of a waterfall is the sum noise of Billions of droplets of water splashing together continuously and simultaneously - it's a type of white noise. Take 20,000 fans packed into a stadium all shouting and jabbering something different simultaneously and all you get is a discombobulated cacophonous raspy rumble. Take 20,000 wave or radio signals and all you get is white noise - which is a cacophonous raspy rumble - audible static.
If you were to isolate one of those noises from the stadium, you might get the sound of a candy wrapper being opened, someone coughing or sneezing, or even possibly a discernible conversation. If you were able to isolate one of the waves or noises from white noise ... Lord knows what you'd get.
What many "Ghost Hunters" and other paranormal researchers hope to capture while analyzing white noise is what is known as an EVP or "Electronic Voice Phenomena". An EVP is touted as a spirit communication from a departed person, a demon or angelic entity.
Thomas Edison was believed to be experimenting with EVP in the form of a 'Ghost-Box', which he never fully developed before his death. See - Edison's Ghost Box
Case of Attila von Szalay
Self styled Psychic Attila von Szalay along with Psychologist Raymond Bayless attempted to record spirit voices beginning in 1941. They at first used a 78 rpm record but were unsuccessful.
In 1956, they switched to a reel-to-reel tape recorder, and they claim they were somewhat successful.[Raymond Bayless - Journal of the American Society for Physical Research. 53; 35-39 1959].
Szalay and Baylees conducted a number of recording sessions with an apparatus they devised. They claimed to have found numerous sounds on the tape that were not heard while recording. They claimed these sounds were spirit voices of . Among the recordings were messages as "This is G!", "Hot dog, Art!", and "Merry Christmas and Happy New Year to you all".
When Edison joined the legions of the dead, he left behind no schematic for his envisioned ghost box, the telephone to the dead. There are however some who claim to have been in contact with Thomas Edison via the very same technology he never actually completed.
Their work is available in Phone Calls from the Dead
Case of Fredrich Juergenson
Fredrich Juergenson, a Swedish artist and performer was recording sounds of nature, birds. When he played back the recordings he heard his mothers voice saying 'Friedel, my little Friedel, can you hear me?' and 'Friedrich, you are being watched' . As per Juergenson when he realized what he had recorded he attempted to re-contact his Mother and other deceased family members
Juergenson joined his Mother on the "other Side' in 1964 but left behind many tapes in which a multitude of voices can be heard. Radio and Audio experts, were unable to pin point a reasonable scientific explanation for the Juergenson phenomena.
Latvian psychologist, Dr. Konstantin Raudive, read of the Juergenson Phenomena and tested Juergenson's techniques. The end result was many voices, including that of what he believed was his deceased mother. Raudive chronicled his work in Breakthrough: An Amazing Experiment in Electronic Communication with the Dead.
In addition to the recordings Juergenson left behind two books on the subject "Voices From the Universe" and "Radio Contact with the Dead." English Translations unavailable.
Starting in the 1960s paranormal investigator Marcello Bacci claimed to be 'dialing in' the voices of the dead using a modified radio.
In 2002 Italian Physicist Prof. Salvatore Mario Festa, attempted to expose Bacci as a fraud, but was unable to. Festa came out a believer as he witnessed the phenomena and was unable to uncover any 'hanky-panky'. He did however write in his report ... "One thing is certain: the voices phenomenon happens only in the presence of Bacci. Then what is the role of the Medium? ..." 
In 2004 Festa attended another session along with a group of seasoned investigators from Italy, Portugal and the UK. They investigators included scientists from various relevant disciplines. They too believe that they eliminated the possibility of fraud. 
William O'Neil and George Meek
In 1979 the duo constructed what they called the Spiricom, a version of a Ghost Box". O'Neil claimed to have received his instructions from a scientist who had died a few years earlier. In 1982, O'Neil stated that he was able to conduct conversations with spirits through his device. Oneil's specs were provided for free to any who wanted them, but failed to meet the requirements of scientific validity. The results he claimed to have achieved could not be duplicated by all who tried.
George Meek, O'Neil's partner, attributed the inability of others to replicate it to O'Neil's mediumistic abilities forming part of the loop that made the system work. This claim would tie in with the investigators of Marcello Bacci who stated "One thing is certain: the voices phenomenon happens only in the presence of Bacci. Then what is the role of the Medium? ..."
In 2002 Frank Sumption introduced his version of the Ghost Box - commonly known as the Frank Box. It is basically a white noise generator and AM radio receiver modified to sweep back and forth through the AM band to select split-second snippets of sound. Skeptics claim the Frank Box relies on coincidental noises and pareidolia. Pareidolia is a psychological effect in which a misconception is derived from an obscure stimulus and interpreted by the Brain as something meaningful, clear and distinct.
In 1901 Anthropologist Waldemar Bogoras used a phonograph to record the chanting and language of Siberian tribes and unexpectedly recorded something quite bizarre. While recording a shamans ritual he also recorded voices taht were not present when he had made the recording, or at least they were not perceived by him.
The recordings are currently the property of NY Museum of Natural History and only the high priesthood of the Scientific realm are permitted access.
Minnesota State University Researchers have been unable to explain them, and it remains a credible piece of evidence in support of Electronic Voice Phenomena.
In the first session an Americanized English speaking voice is heard - mimicking the shaman - the voice seems annoyed, as if it resents being drawn into the shamanic ritual - but culminates with the English speaking voice laughing.
Another session records a wolf clearly howling as the shaman beat his drum and chanted.
The Bogoras incident would also tie in with the hypothesis of a 'medium' personality being present - the shaman being the medium.
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Footnotes and References
1. A PARTICULAR EXPERIMENT AT THE PSYCHOPHONIC CENTRE IN GROSSETO, DIRECTED BY MARCELLO BACCI
2.REALITY OF INSTRUMENTAL TRANSCOMMUNICATION VOICES SCIENTIFICALLY DEMONSTRATED