When I was a boy, I discovered a magnetic reel-to-reel audio tape recorder that my father had used to create "audio letters" to my mother while he was serving in the Vietnam War. To my delight (and his horror), I could listen to many of the old tapes he had made a decade before. Even better, I could make recordings myself and listen to them. However, all of my father's tapes were decaying to some degree-flaking, stretching and breaking when played. It was clear that these tapes would not last forever, so I copied a few of them to new cassette tapes. While playing back the cassettes, I noticed that some of the sound quality was lost in the copying process. I wondered how many times I could make a copy before there was nothing left but a murky hiss.
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