Isolating Electronic Voice Phenomena
A Step By Step Guide to Noise Reduction

There are many free audio editor apps available. Most of them have the features you would need:
Reverse, Noise Reduction, Pitch Control, Speed Control, and Scrubbing.

1. OPEN YOUR AUDIO FILE...

IN THE AUDIO EDITOR OF YOUR CHOICE
And make a copy! Better yet, find the section containing the EVP, highlight it, copy and paste it into a new file.

2. NORMALIZE YOUR NEW FILE

NORMALIZATION IS A PROCESS THAT BRINGS THE AUDIO LEVELS UP TO DIGITAL ZERO (maybe a few dB less)
Typically in the EDIT menu. When normalizing, be sure that either ALL or NONE of the file is selected, otherwise only the selection will be normalized.

ORGINAL CLIP

NORMALIZED CLIP

3. SAMPLE THE NOISE FLOOR

CHOOSE A SECTION OF NOTHING BUT THE BACKGROUND NOISE AND HIGHLIGHT IT
Usually called Noise Reduction (maybe Hiss Reduction), this process will store the mp3e information for reference.

SELECT ALL or DESELECT ALL. AND THEN...

4. APPLY NOISE REDUCTION

REMOVE/REDUCE THE NOISE FLOOR
All files are different and may require some manipulation for best results. You should have the option to preview the noise-reduced file before you okay it (if not, find a new audio editor). Over reduction will result in digital distortion (high-pitched bell sound) that could make the EVP less decipherable than no action at all.

NOISE REDUCED FILE

BEFORE Noise Reduction

AFTER Noise Reduction