The History ...
Voices from beyond can easily be recorded using a regular cassette tape recorder with an external microphone or a digital voice recorder. The discovery was made in 1959 by Friederich Jurgenson, a Sweedish researcher, and it started a wave if interest in this field. Jurgenson was using a common tape recorder to record bird songs when he discovered mysterious voices in the recordings. Mixed with the backgorund sound, the wind shaking the leaves in the trees, it was possible to hear the conversations of people who were not visible in the place where the recordings were made. After Jurgenson's discovery, many other researchers began to experiment, trying to pick up voices from beyond. The most important of these researchers was Dr. Konstantine Raudive. He died in 1974 but left a number of works aimed at convincing humans that contact between the dead and the living is possible. Dr. Raudive applied the principal of stochastic resonance to his research. The basic idea is that background noise acts as a carrier and can be modulated by any other signals present in free space. Without background noise, these signals, (voices of the dead), are too weak to be detectable, but in the presence of a noise (white noise) their levels increase beyond the threashold of detection and become clear...sometimes even loud. White noise can also be describes as a signal with no definite frequency. 

The digital voice recorder allows one to record during investigations, play back later during analysis, and inport directly to a computer for further enhancement. 

This recorder is small and easy to carry.  You can also use the voice activation feature so there is less audio to review.    I use this for my notes as well.  Most units record the time of the recording as well which is very useful.  When using audio recorders be sure to state the location, time of investigation, and investigators names.  When recording investigators names it would be wise to have each individual present state their own names, which will make it easier for distinction amongst voices heard on the tape during review.  Voice activation mode should be deactivated on tape recorders during use when electronic voice phenomena is trying to be achieved due to the fact that it usually cuts off beginnings of words, sentences, and phrases.   This is not necessary with digital recorders and they actually seem to work better in voice activation mode. (Troy Taylor)