Electronic Voice Phenomena or EVP is a voice of Spirit captured on an electronic recording device such as a dictaphone. Of course this is debatable and the sceptics will insist that it is the frequencies of other electro magnetic equipment interfering with the recording equipment. Although this may be the case at least in some circumstances I am of the belief that EVP is a genuine phenomena and although I have heard many dubious, almost deperate, recordings EVP remains to be one of my most convincing methods of proving the afterlife.
The question asked most often is why can we only hear the voice via the recorder? Well I'm no expert but I would summise that the EVP is on a different frequency to what we can hear much like the sounds that some animals emit such as a bat which is also inaudible to the human ear without special recording equipment. So with that in mind it has got to make you wonder that if there are things we cannot hear without using technology are there also things that we cannot see...."just because you can't see it doesn't mean its not there"
Roses theory on EVP recordings is that only grounded/ Earth Bound Spirit may communicate via this method. Her reasoning for this is that if any Spirit may use EVP to communicate then loved ones would be captured as they would be the ones keen to contact you, however this is rarely, if ever the case. It seems a logical theory.
A detailed explanation of EVP can be found at
Wikipedia - EVP which makes for a very interesting and informative read.