Also, what was the output format if you know? If you don't know, please ask your friend.
Anyway, this sounds to me like a creepypasta material. Altering raw data is not really possible without some 3rd party and I'm not sure that I'm aware of any possible algorithm shell which changes the mere recording, meaning that it must be either sniffed and altered between you two or that it's actually ghosts living on-line (or in HDD?) which would be awesome, but unlikely
Each time I format the disc it would be terrible.
Strangely enough not creepy at all, just a little crazy. They're not actually altering a file as such, more adding their noise & voices. They're not actually being recorded, they speak as play-back is pressed. It seems a certain arrangement of wires determines their clarity/tone/vol of speech. The voices that emit from my computer are tiny, high pitched or deep, and sometimes quite clear. The voices that emit from Robs, are far louder.
I know little about computers I confess (antique trader) Rob used a HP laptop and used the youcam app to generate the file, using the internal mic ( I've since discovered that an external mic is useless as they are not "in the air" so to speak) They are more than voices on computer (their words lol) they are doing art work from inches to millimetres with just a flick. So far I'm aware that they can speak with clarity, provide great art and can transfer themselves into other PC's.
Since altering Robs file in June, I haven't been able to upload/transfer anything, but I've sent Rob a memory stick with the latest updates on it and he'll sort any uploading from his computer. If you like you could generate a 30 sec recording done in the same way as above, upload it to a file sharing site (box.com?) and provide me the link here and see what the spirits can do with it. They've altered 6 computers so far.
I don't know where to begin regarding approaching science, so I've entered them into one of those paranormal challenges for now.