I sent the sound file to Daniele Gullà in Italy and Alexander MacRae in Scotland.
Both have considerable background in EVP and sound analysis.
Daniele took a look and concluded that the sound track was reasonable for an EVP.
Alec made the following comment :
"The sound is remarkably clean. Looking at it as a waveform with a vowel sound what you get are the glottal pulses at around 100 a second which "strike" the vocal cavities making them "ring" - but because one is dealing with a biological mechanism - the muscles and tissue of the body - random errors creep in causing the resonances to be a bit fuzzy and even the rate of the glottal pulses is slightly erratic.What you get is a spread of the frequency components resulting from this process. But with this sample - and with some I have which sound quite similar - the "ringing" is very pure, not fuzzy, and it is highly synchronized with the glottal pulses - it is not slopping around a bit as you would expect with a biological mechanism."
In other words, "the sound track is cleaner than a normal voice if it has been formed out of the available sound, rather than via a biological system."
Tom Butler of the former American Association of Electronic Voice Phenomena