Electronic Voice Phenomena are known as
Raudive Voices - Intelligible voices recorded on magnetic tape under
conditions of silence or white noise that are heard only when the tape
is played. A phenomenon discovered by Konstantin Raudive.
Some refer to these voices as the voices of the dead. Where these voices come from or what they may be are only theorized in many forms but still yet to be defined.
There are two methods to use when attempting to record EVP's. You can use any recording device but prepare to get the quality expected of the instrument you use. Many investigators choose to use Digital Voice Recorders because you get a clear, crisp recording while not having to deal with using a new analog tape with each recording. It is also more efficient when needing to target a specific frame in your audio. Analog recorders are still used in the field by many, as well, and we usually have better luck capturing EVPs with this type of recorder. An external microphone is recommended so you do not record the inner sounds of the devices mechanic process.
The first method is to start your recorder. Announce the case, time and other notations so you can easily define from which investigation the audio is from. Then you can do what is often called, an EVP sweep, where you carry your recorder along the premises inquiring from any entities in the area, a defined answer.
When asking your questions, allow 15-30 seconds between each, allowing enough time for an entity to reply to you.
The second method is to leave the recorder in a locality and return later to see if you've captured any EVP's.