EVP or electronic voice phenomena are the recordings of voices of spirits of the dead.
A tape or electronic recorder is now an important piece of equipment for ghost hunters. Returning to a sound board and using expensive precision equipment, all background hissing noises can be analyzed for endless hours to detect voices hidden within. Voices might be sped up or slowed down tremendously so all recording speeds are tried. Then when an indistinct rumble is heard, skilled investigators with a lifetime of skipping English classes and listening to loud music are called in to interpret the sound. Spirit voices are always found saying interesting words or phrases, like "cheese" or "nurglemumph".
Another type of recorder scans radio stations or a stored group of words to help spirits choose and form words and phrases. As in real life, these expensive devices reveal that the spirits are always talking about laxatives or murder as they did in real life. And it also seems that in the case of stored dictionaries, investigators have discovered that ghosts have picked up Chinese words and Chinese-accented English despite being from any other country.
Critics ask why investigators never hear, sneezing, belching or farts in EVPs, but ghost hunters note that the technology hasn't reached that level yet.