Digital information is lossless. You can copy a file from hard disk to floppy to CD to flash stick to … and it will still be the same file. But if you use analog media, such as good old tape, you can rely on the opposite: The data you read from the medium will definitely be different from what you wrote onto it. Anyway, there are many ways to hide secret information in the sound on an audio tape. This article shows you one way of doing this… Link.