Electronic Voice Phenomenon

I have used recorders from Olympus before professionally, they typically do a good job.  What is important is the frequency response, digitizing frequency (sampling rate), and ability to download to a PC.  Lesser models do not have those three characteristics combined.  Frequency response should be as close to 20-20,000Hz as possible.  Sampling Rate should be a minimum of 44,000 to meet Nyquist criteria.  In the process of digitizing an analog signal such as sound from a microphone, the minimum samples needed is twice the highest frequency.  So if your highest frequency is 20,000 Hz then your sampling rate or digitizing rate should be 40,000 Hz.  These recorders are small, reliable, and easy to use though their frequency range is limited to 200-13,000.  They use two AAA size batteries. The Olympus WS-400S offers better frequency response, 50-19,000 and takes one AAA size battery, has stereo microphones but is slightly more expensive.

Digital Voice Recorders

Olympus VN-6200PC

The theory behind disembodied voices is that spirits can manifest sound energy or electromagnetic energy for voices.  Sound energy is a pressure wave, a result of mechanical energy not electromagnetic.  Like a drumstick hitting a drum.  The drum reverberates sending out undulating waves of pressure through the air.  Interestingly enough, the speed of sound (as with EM) differs depending on what medium the pressure waves are travelling through.  For sound, mechanical energy, the denser the medium, the faster the sound travels.  Electronic recorders have the ability to pick up both mechanical and electromagnetic energy in the vocal range (20Hz to 20,000Hz).