system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5 - how is music “remastered”

How can an audio engineer take a thirty-forty year old song that was recorded on analog tape?  How is the data extracted and processed?
gpt
"Mastering" is the process of taking a mixed song and preparing it for radio play/album printing. For a remaster, they will typically get ahold of the original mixed tapes and do the mastering process over again. A lot of old music was recorded analog with great equipment, so the stems (individual pieces of the finished whole, think single tracks) are usually in pretty good shape fidelity wise. Digital mastering technology and mastering techniques have come a very long way, so what you *typically* end up with is a much higher fidelity (and usually louder, but that's a whole separate story) new master. Ultimately though, the quality of the remaster depends entirely on the ears and equipment of the person doing it.