Every paranormal show worth its snuff eventually whips out the EVP sessions. What is EVP? Is EVP a real thing? Well… it depends!
The term stands for "Electronic Voice Phenomena," and describes sounds - usually voices - which can be heard on electronic recording media, but which were not heard at the time.
The term covers any kind of electronic recording device, from a video camera to an MP3 recorder and everything in between. Back in the day, EVP used to be recorded on 4-track tapes or on mini cassette recorders. These days, most EVP are recorded on digital recorders like mini-DV or hand-held MP3 recorders.
Let's say you're in a haunted location, and you have an MP3 recorder sitting on the table beside you. At the time, you don't hear anything unusual. But later when you listen to the recording, you hear a voice. That's an EVP. (If you had heard it at the time, it would just be "a voice.")
The theory among believers is that spirits can somehow interact with recording devices more easily than they can interact with us out loud. Many people believe that spirits are electrical in nature, that they are able to manipulate electrical fields easily. This is what explains cold spots - the spirits are drawing energy from the air in order to manifest, which makes the air cold.
If you have an easier time manipulating electrical fields than you do resonating the air to make a noise, then you will find it much easier to "talk" at an electronic recorder. Physical recording devices like cassette tapes record using magnetic media, which are easily manipulated with electricity. Digital recording devices rely on electrons, which are probably even easier to manipulate in that sense.
The problem with EVP recordings is that they are often so vague and open to interpretation. If your dead uncle Phil wanted to say hello, don't you think he would say "Hello"? Instead of "mumble mumble hiss"?
Although it is theoretically easy for spiritual energy beings to affect an electronic recording device, it's also easy for other electrical interference to do so. Even in the absence of ghosts, a recording device can pick up snatches of radio waves, television broadcasts, HAM radio chatter, CB radios - you get the picture. We are awash in unseen electrical interference, any of which could easily lay down a brief recording on a handheld MP3 player.
One thing you will notice is that an EVP session's playback often has the volume greatly boosted. I guess you have to crank up the volume in order to hear those whispers! This only adds to the likelihood that the EVP is simply an electrical artifact.
If you listen hard enough, with the volume loud enough, you can hear all kinds of things on an otherwise-empty recording. This is particularly true of physical media like cassettes, if the cassette is being re-used. It is also true of digital recorders, because the previous recording isn't always fully erased.
Creative Commons-licensed image courtesy of Flickr user John-Morgan