The issue with a EVP recording is that you do not know where the sound is being projected from.
Multiple microphone placement can help to define an approx location if the sound/voice is a single source and from a defined area. The Roland R26 recorder that I use has four microphones, two forward facing directional microphones and two multi direction microphones, so with this recorder if the sound/voice is being emitted from behind and left of the recorder then I can within a scope of 90 degrees suggest approx the direction the sound/voice came from by analysing the volumes of each recorded track.
If you can see a person speaking ten feet away then it's not difficult to record that voice, it's also a single sound source. It is not improbable that EVP is from multiple unseen sources and that brings with it a whole load of problems to the point it can become guess work where the best place is to record EVP and maybe even the use of multiple microphones is a consideration you need to make as well as placing recording equipment at multiple locations. The different microphones available will make a difference and there are multiple types of microphones and each one performing differently. We will be looking at microphone types later on in this web site. For the moment let us look at an example of recording events of which will be useful to you for when you attempt to record EVP.
I would like you to look at the above picture of three rooms in a Hotel. Each room has a recorder fitted and will record 30 minutes of time. Get a note pad and write down what your own findings are.
Let us imagine you are staying in this Hotel and your in Room 3 which is next to the road. Your trying to sleep but in Room 2 there are two guests arguing. You then turn up your radio to listen to some rock music but at a volume that drowns out the commotion next door.
The guest in Room 1 is having a relaxing meal with his wife and also hears the commotion from Room 2 and turns on the TV to a volume that also drowns out the noise from Room 2.
Here is an interesting question for you to consider, If you listened to each recording what would you expect to hear? And what are you hearing?.
The correct answer to this question is you simply don't know, you do not have enough information. If some one gave you three recordings and a simple map of the rooms it would be impossible for you to analyse it accurately, you need much more data/information. This forms an important area which any researcher of EVP would need to consider as critically important.
The human brain is extremely clever but it does have it's limitations. Here is an example; Your sat at home with your partner who is watching their favorite football team in an important cup match. You hate football and completely board - I am sure you have been there!. You ask your partner how the game is going - you get no answer. The reason for you being ignored is your partner is using so much brain capacity that it has little left for other things even though the task the brain is working on is simply watching TV.
You on the other hand are multi tasking, your half heatedly watching the football, looking through the window at the car that is pulling up, your thinking about what to do, should you read? listen to music? go on the internet?. You will also find that the time goes very slowly yet your partner will often say 'half time already!'. We have already touched on how the brain uses hearing depending on the circumstances, remember the Brides Fathers speech recording example? The recording was nothing like what was heard when the recording was being taken.
Looking again at the above example. If I was to say the walls between each room are of simple plaster board except the right wall of Room 3, which is of solid brick. The recording microphones were placed in the left corner of each room and on stands 2 feet above the floor. All the floors were carpeted. I draw on each room a diagram of the position of the bed and furniture, electric wall sockets, windows, room size - height, width length. People present and where they were located. The temperature of the room. The date and importantly the time of the recordings. Area of hotel, close to main roads such as motorway, airport, train stations. Weather, raining? dry? thunder? Lighting?. The microphone used was omni-directional.
I am sure you now realise the importance of data. Let us break this down into single points and the significance of each piece of information.
SIZE AND SHAPE OF ROOM.
All rooms have differing acoustic properties. A recording in a small apartment full of furniture will sound different to a recording in an empty Church. The larger the room the more reverb you will hear as well as echo (sound being projected backwards). Square rooms again perform more acoustics tricks than a circular or oblong shaped room. Working with bands, solo artists as well as my own live performances takes me into a large and varied number of venue locations, each venue differs greatly so sound checks become your first task and get the best sound possible and more often than not it is a compromise.
Brick, stone and plaster all react differently to sound. A plaster board wall will absorb sound and pass it through to the next room, where a brick or stone wall may (depending on thickness) deflect, absorb and pass through far less sound. A good example is you clear your living room of all furniture and strip off the wall paper to bare plaster. You will notice that when you speak the sound becomes hollow sounding - reverb. You hang new wall paper and the room suddenly becomes less hollow sounding. Certain frequencies react differently to solid objects and one of the first frequencies to loose is bass and a sound becomes thin sounding. This is one of the reasons when you go to watch a band their speakers are stacked high so sound projects over the heads of the audience. You will also notice the bottom speakers are much larger in size, these are bass speakers and are larger to compensate for 'bass frequency loss' as the sound passes through and absorbed by peoples bodies. Different frequencies need different power outputs to project a sound the same difference.
When assessing a room note where the room windows are and if they are open or closed. What are the windows made of? Single wooden types or double glazed? Wall vents and part opened windows will cause drafts and account for cold spots as well as sound sources if air is blowing an object about.
ROOM FURNITURE MATERIALS.
Furniture, for example sofa material, affects sound. Leather will bounce sound back where a softer foam material will absorb sound. A empty wooden book case will affect sound differently to one full of books which would absorb sound. A great example of recording a voice is to look at a singer recording in a studio.