I have a cassette tape recording of a spoken radio interview. The first half of the recording went bad years ago. Now, whenever I play it (regardless of the tape player), it sounds something like this:
The damaged portion is 14 minutes long. As the recording plays, it sort of recovers gradually. Finally, at a station break, the audio finally becomes perfect again. I have about 6 minutes of good audio after the damaged 14. The audio clip I shared above is from the end of the damaged section -- the beginning sounds much worse.
Can anyone tell me precisely what is wrong? Is it "distortion"? Did the tape get stretched or something?
And is there any way to fix the audio digitally so that the voices at least become understandable, even if the quality remains poor? If so, what filters or techniques should I use?
(I own Amadeus Pro for the Mac, but don't know much about very technical audio work)