Posted 17 May 2005 - 09:01 PM
The reason that "white noise" is preferred in EVP recordings is due to a phenomenon caled "stochastic resonance"
Now, white noise is "random" noise. This is important, because stochastic resonance(SR) can only occur with random noise.
Sources of random noise include running water from a faucet or waterfall, static audio from an off-channel radio or tv station, etc...
Interestingly enough, white noise is also automatically created within the electronic recording circuitry of inexpensive digital recorders, making them somewhat ideal as an EVP recording device. The more expensive digital recorders tend to filter out the internally generated white noise, so avoid using expensive digital recorders for EVP use.
OK, so what is stochastic resonance, and what does it have to do with white noise and EVP? Well, first of all, stochastic resonance(SR) is a phenomenon that was discovered completely apart from EVP, and is used in advanced signal analysis. So even if one does not believe in EVP, they can believe in SR, because it is a scientific fact.
Anyway, what SR does is this: If a signal is so weak that it can not be detected by a device, it was discovered that introducing white noise along with the weak signal created a dramatic effect... it creates a "resonance" and thus amplifies the weak signal so that it can now be detected(or recorded)
If you do a GOOGLE search on stochastic resonance you can fing some interesting reading on this effect.
Anyway, it is thought that the use of white noise while recording potential EVP voices amplifies the voice on the recording(which is why you do not hear the voice until playback) The use of audio-editing software can further enhance a suspected voice.