Pixel42
Schrödinger's cat
If you had headphones on then how do you know whether or not the room was completely silent whilst you made your recording?There isn't a budgie present, its probably/possibly/likely noise from the spirit world, or not. The sentence I hear, I have never said before in my entire life. If you listen @ 0.5 seconds, there is a more quiet high-pitch voice saying "She wasn't speaking"
I asked jsfisher to block the image off the recording. I'm in a quiet room, I have head phones on, and my lips are closed at all times.
My best guess for this particular recording is that a couple (the woman of whom had a voice similar to yours) loitered outside the window of your library having a quiet conversation whilst you were making it, and you only noticed them when you played the recording back some time later. A car radio playing outside the window is another possibility.
The bottom line is that there are perfectly adequate non-supernatural explanations for everything you've so far presented here, whether it's pareidolia, interference or living people's voices recorded inadvertently. Unless you can produce evidence for which the supernatural is the only possible explanation (like a checksum for a file on someone else's computer changing spontaneously), we must by default assume a non-supernatural one. Do you understand why?