There is a wide range of programs and price ranges concerning the ability to analyze audio files and detect EVP. Some people prefer high end over low end software, but many of these programs have many more bells and whistles than are needed.
Although one might be inclined to filter and manipulate an audio file until they get a clearer EVP, what many fail to realize is that the more you filter an audio file the more you take away the aspects that make up the audio you are listening for.
A filter used to heavily may actually take out an integral part of the audio and make it sound much differently than it would if left complete (it might be a high note, an inflection or slight rise in tone that is actually chopped out of the file). Think of it like cropping a photo. How much do you crop before you lose the integrity of the subject matter that was captured in the original?
Although using filters may help you personally make sense of an audio file, that manipulated file should NEVER be used or submitted to others to validate communication. Generally speaking you should always keep your original file intact and available if you foresee the need to have someone else validate your analysis. Additionally, there are two important things to keep in mind.
- Although amplifying may often be needed, filter your evidence as little as possible. This included noise reduction, stretching, varying the pitch or tone etc…
- When clipping and audio file for evidence, you should try to have an investigators voice in the clip for comparison to the claimed EVP portion of the clip. Significant differences will be very noticeable.