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Analysis of EVP

Article: PRAB-CI-968
Article by: Ian Murphy, Paranormal Research Association of Boston

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This article deals with the considerations in the collection of and analysis of EVP’s (Electronic Voice Phenomena), also known as disembodied voices, ghost voices, or my personal name for them “Audio anomalies that bear the characteristics or likeness of voices of persons not physically present at the time” (AAtBtCoLoVoPnPPatT). However, for the purpose of this article, I will refer to them in their most well known acronym, EVP.

Section 1: Collection of your raw data.
There are many different methods of collecting the raw data, or audio, for your EVPS. The best advice I have is to try all the methods available, and attempt to vary the ways you use them or create your own. As for the equipment, you can either opt to use magnetic tape cassette or digital audio recorders. I personally prefer the digital audio recorders as they do not have moving parts (so do no pick that up in the recording) and they are easy to send to the computer for analysis.

1.0 General Best Practice
When you are recording audio in the attempt to gather EVP raw data, the following rules should be applied to greater help you in analysing your data.

1.0.1: Record onto the start of your session the time/date, case file reference, the person making the recording, the location( room and site), weather conditions, internal temperature and any EMF findings.
1.0.2: If using a locked off recorder, make sure to announce yourself to the recorder. This cuts down on false positives.
1.0.3: Gather a sample of the people present to compare to later.


1.1: The Static / Lock Off Method

                In this method, the recorder is placed in a locked off room. The recorder is simply set to record and left to run. In an attempt to lessen the amount of data to analyse, some people and groups will engage the recorders “Activate on Sound” function.  I personally don’t agree with the method, as the sound thresholds can be too high to trigger the recording, meaning they miss the sound, and they (if the sound was loud enough to trigger at all), especially on tape recorders, can take a second to kick in, meaning you may miss the sound event itself.
                This method can also be used when just holding the recorder.

1.2 The Challenge / Response Method
                In this method, the investigator asks questions and hopes for a response. It is best practice to leave about 10 seconds between questions to allow a response. It is best to avoid questions requiring only a yes or no answer. This is because these are short words and simple background static could be mistakenly identified as a response.  This is the most often used method.

1.3 The Antagonistic Method
                This method, favoured in Europe, is a method where the investigator uses antagonizing phrases to trigger a response. This method can be more effectively used if you research the history of the location. For example in a jail (prison) if you use terms that would aggravate the guards it is more specific to that group.

Section 2: Data Transfer

This is possibly the simplest part of the process. It is moving the data from the recorder to the computer. Using a digital recorder, simply follow the method described for your device. In an analogue recorder, attaching to the line in and recording it to the computer is the preferred method.


Section 3: Analysis
Whenever you are analysing an EVP, remember to take into account:
The Location: Was it indoors or outdoors.
In an outdoor location wind can cause a sound to travel.  You may be hearing voices from a town over a mile away. You will also pick up animals native to the location. A fox can sound like a horrific scream
In an indoor location, look at the building itself. Is it well insulated or gaps in the walls or windows. How long are the corridors? Long corridors can create infrasound.

Who was present? Do any of the EVPs match a sample of people that were present in the location?

Is it a voice: Are you sure?

Frequency of the anomaly:  Does it match anything present? Such as a printer, an insect repellent?

How loud was it? Determine the distance based on how loud the sound was.

3.1 What am I looking at?
You may have seen these around. But what are they. Basically, they are graphical representations of the sound you are listening to. There are many programs out there that can be used for this, they range from free and shareware to the more expensive programs like Adobe Audition 3.







Figure 3.1: Spectral Display








Figure 3.2: Waveform Display
3.2 Characteristics of a sound wave
A sound wave has three important characteristics, which are

Frequency: The  number of waves created or received in a given length of time. Frequency is measured in Hertz (Hz) or Kilohertz (kHz). The frequency range of normal human hearing extends from around 20 Hz up to about 20 kHz.

Amplitude:  The result of the waveforms that are created when we talk, loudly or softly.
Amplitude of the waveforms is measured in Decibels (dB).  The greater the amplitude, the louder the sound.

Phase:  The time interval between two similar events. A waveform travels 360 degrees to complete one cycle. When two waveforms cross the reference line at the same time, and in the same direction, they are said to be in phase. When two waveforms cross the reference line at different times, or are travelling in different directions, they are said to be out of phase.

3.3 What to look for in a waveform
When you are analysing the waveform, pay special attention to the amplitude and frequency of the file you are looking at. If there is a raise in the amplitude above the baseline, there is a sound there. It is then up to you to listen to carefully to the sound. Then check the frequency of that raise. Is there any repetition in these frequencies? If there is this could indicate a voice, or an animal call. But it could as easily be a manmade function such as a refrigerator cycling.


Section 4: Manipulating the wave
When you are manipulating a wave form you have to be very careful. Firstly, you need to make a copy of your original file. Never, ever, work direct on your master file. If your computer loses power or crashes, you may have ruined the integrity of your file as the program may have auto saved direct to the file.

When you are listening to your data, play the file through fully at least 2 times. While you are doing this, log down any anomalies that you hear on your log sheet. This will help you to keep objective during the file and allow you to look over, in depth, the file again.

4.1 After the isolation
After you have isolated a part of the file you want to listen to closely, you may now:

4.1.1: Removing Background noise. As you will have a lot of data where there was no sound, you can use this to isolate the frequencies of a background noise to remove. This is mainly helpful if using analogue recorders, as it can remove the sound of the working parts.

4.1.2: Amplifying the source. Using a gain tool, you are able to effectively make the sound louder, while holding on to the integrity of the original sound.

4.1.3: Remember to document the changes made. This will help you and others looking at the file.

After this, you may be tempted to apply more filters to “clean up” your file. I would advise against it as over filtering can make a barking dog in the distance sound like an evil voice telling you to “get out”.

4.2 Sharing your data
If you want to share your data with another individual, team or community program, it is best practice to send the unaltered file, the unaltered isolation and a log of any changes you made to any isolated clips.

It is best not to tell people what you think you hear, as this will lead them to subconsciously listen out for this. It is better to get back their opinions and see if they correlate with yours.

Section 5: Conclusion
Firstly thank you for reading this document. It was a pleasure to write and to attempt to give something back to the community that has been so good to me.  I hope the methods and explanations above help you in your future endeavors. If you have any questions, feel free to e-mail me.

Section 5.1: Contact Details
Author: Ian Murphy, Paranormal Research Association of Boston
E-Mail: This e-mail address is being protected from spambots. You need JavaScript enabled to view it
Website: Paranormal Research Association of Boston


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