Ken Caillat Seeks Input for Book

[bucklind17]

I remember reading/hearing that at some point in the recording process, the master tapes began to lose the high end. I'm not very knowledgeable about what exactly would cause something like this to happen outside of overuse but was curious what kind of process goes into restoring that. Did the tracks have to be entirely re-recorded or just the affected aspects? What songs, if not all, were affected by this and did any changes to the final tracks occur because the originals weren't usable?

Sorry if this is a boring question or something that's more well known to most than it is to me. I'm oddly curious about it!