From Wikipedia, The Free Encyclopedia.
Electronic voice phenomena (EVP) are anomalous voice or voice-like sounds captured on a variety of recorded media. Typically they are brief, the length of a word or short phrase, though longer examples are not unknown. As with other paranormal phenomena, EVP and the principles behind it are disputed and attempts to replicate it under laboratory conditions have so far been unsuccessful. Results of various EVP experiments have been published, but no literature supporting the phenomena has appeared in mainstream peer review scientific journals.
The history of EVP research is a subject on it's own, so I will cover it elsewhere!
Basic equipment needed:
It is best to use an external microphone with a tape recorder, as the internal microphone tends to pick up on the noise from the internal mechanism, making it even harder to try and hear anything recorded on the tape! It is also best to use a cassette tape deck with mechanical controls that allow easy, repeated review of the noises, it is also helpful to have a counter so you can take note of where on the tape the noise is (making it easier to find and share with other people).
Digital Voice Recorders are a popular choice, but they are best used with a computer to analyse and store the recordings, requiring additional software.
Microphone—An external microphone is a good investment, so spending on a good quality one is worth it. There are many different types I personally use a boundary microphone with picks up sound from 360°, although I also have standard uni-directional one for interviewing.