Headphone Phase Reverser |
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COMMENT??? Got A Question??? A Click on the Wizard opens Technical questions or just want make |
A common problem with EVP occurs when you return from the field and spend hours trying to decipher what the voice you hear in the background actually says, if anything at all. You listen repeatedly and still you are not quite sure. If only there was a way to clarify it a bit more. Well there may be. But first, a little about listening in general.
Experience has shown that you should listen for only a few minutes at a time. Otherwise the sound becomes imprinted and you may not hear it as it actually is, rather what you perceive it to be. The constant background noise on the tape as well as its repetitive nature can tend to blur your ability to hear certain characteristics of the sound. This will impair your ability to properly determine the EVP. To minimize this you should keep your sessions to less than 15 minutes at a time. Take a 15 minute (or more) break between each session.
Secondly, you should use headphones, not loudspeakers, to reproduce the audio. Speakers tend to fill a room with sound. This can create echoes from walls and other items in the room. The general acoustics of the room also becomes a factor. This is undesirable because in most cases you are not in the same room in which you captured the EVP. The tape containing the EVP has also captured the acoustics of the room in which it was made. Combining the two creates a false environment and can lead to problems. While it may be alright to play an EVP over speakers for multiple listeners to hear, it is not advisable when you are actually working to decipher it for your research. Use headphones for this.
The type of headphone is also important. You should avoid the cheap kinds that do not cover the ears. These allow outside noise to intrude on your EVP and create problems getting the true sound reproduced for you to hear. They also do not transfer all frequencies linearly, lacking especially in the low end. Larger headphones that completely cover the ears do not exhibit these undesirable characteristics. The improved sound transfer makes EVP much easier to hear and understand. This is the primary reason many researchers use "noise canceling" headphones. These are much more effective at blocking ambient noise than regular headphones.
So now that you are using good quality headphones and doing so in short sessions, is there anything else that might help? Actually there is, that is the purpose of this report. When sound arrives at your ears, it is generally in phase. It strikes both ears at about the same time. The sound pressure will act on both eardrums simultaneously, pushing them in and out together. This is how we normally hear sound. In the case of an EVP recording they work together. The EVP and any background noise cause the eardrums to respond in phase with each other. But there may be an advantage to shifting the phase of one ear.
Much noise is random in nature. The brain is conditioned to accept sound in phase. So if one ear is placed out of phase with the other the brain will not respond as well to those signals which have been shifted. This is the concept behind the phase shifting adapter for your headphones. It will cause the sound to one ear to be shifted out of phase with the other ear. In so doing, certain sounds will be attenuated by the best processing device available, your brain.
Another benefit of using a phase shift is being able to change between modes easily. This minimizes the hypnotic effect of the background noise since switching between modes breaks up the monotonous sound. It will allow you to remain more alert as you go through your tapes. You will be able to better utilize your sessions since you will be more attentive.
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This is a schematic of the headphone adapter. It provides a switch to change easily from normal to phase shifted modes. An additional switch allows a stereo signal to be combined into a monaural one so both channels may be shifted together. |
Construction is straight forward. Simply mount the switches and jack in a box to protect the components. Wire the switches and jack according to the schematic above. The unit should be placed in a shielded enclosure to insure against outside interference if it will be used in an area subject to strong electromagnetic fields. Otherwise any plastic or metal enclosure will suffice.
The Monaural Switch allows two channels to be combined if the unit is used in a stereo system. It will also provide a signal to both ears on those players which do not have provisions for a dual earpiece headphone. It may be used in conjunction with the Phase Shift switch to try to bring out EVP if difficulty is encountered.
In short, this unit may help you hear your EVP more clearly. There are not any set guidelines as to when to use what function. EVP is an unknown in itself; What works on one may not work on another. It will do what it is intended, that is create the phase shift between your ears on a set of headphones. Beyond that, no promises are made.
Happy hunting, and many good EVPs!
If you would rather purchase a Headphone Phase Shifter instead of building it
yourself, a fully assembled and tested unit is available. The price (U.S.)
is $19.95 plus actual shipping costs. E-Mail me for more information
(NOTE: Since choice of headphones is user's preference, they are not included )