system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How are songs remastered?

It seems that on Spotify all the Beatles songs are remastered. What exactly is a remastered song, is it not just re-recording a song?
gpt
Remastering basically has two components: reworking the mix and "restoring" the audio.   


Studio gear, even back in the day, typically records each instrument and vocals onto separate tracks.  That's re-balanced, along with often having some equalization applied, to provide a "polished" final sound for various audiences.  FM isn't very good at transmitting the highest and lowest audible frequencies, and back then a lot of audio gear wasn't good at reproducing the highest frequencies either. So an old FM mix tends to have boosted bass around 80hz and treble somewhere in the 7k-10k range to give the impression of a "full sound" where a vinyl production wouldn't have those boosts.  Things like that.  So in a remaster they re-work the balance between those different studio tracks (where it's still available) and tweak the equalization to match modern tastes.   


For "Restoring" the audio, there may be loss from the recording material, the microphones themselves weren't great at recording the highest end and some things like that.  We have algorithms now that are intended to bring out or clean up missing or distorted sounds from technological differences, degraded recording media and so on.   It may be cleaning up static or trying to restore the very upper end "sparkle" to things like cymbals or sibilance to the "s" sound in vocals.   Bringing out that kind of thing is more art than science and is a lot about taste.   


So...that's what a remaster is for, adjusting the mix to modern tastes and playing around with some equalization/digitization magic to try and make it sound like a brand new recording on the best gear.