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Comment by baddox | Hacker News Reader

It's not irrelevant. If the exact same recording of a song appears on two albums, an ideal categorization system would allow it to appear as such without storing multiple (redundant) copies of the song. An easy way to think of it is a normalized relational database. If the song has an id of 5 and is on two albums with id 2 and 3, then there would be an AlbumSong join table with schema (album_id, song_id) and two rows: (2, 5) and (3, 5). It should be irrelevant which album you ripped or downloaded first.

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    >  If the exact same recording of a song appears on two 
    >  albums, an ideal categorization system would allow it to 
    >  appear as such without storing multiple (redundant) copies 
    >  of the song.

I don't agree. The song was released twice; if you have both albums, you ought to have two copies of it.

Yeah, it's not going to be a big storage hit in reality (and even if it were, you could just rely on file system level compression/deduplication). I, like the author, just enjoy musing about the "perfect" way to organize a music library.

Some artists re-record or alter their song on secondary release. Or if it is live performance.

Deduplication should be done by algorithm that detects that it is same binary copy -- not through tags.

Blue Oyster Cult are one of my favorite bands. I have many of their "greatest hits" albums because they release one every few years, and frequently there will be a few previously unreleased tracks that are worth having.

This means that in my iTunes library I currently have seven copies of Don't Fear the Reaper. Three of these are copies of the studio version. Incidentally, I hate this song, and though I think you're right and I should have two copies of the song, I can't help but react with mild revulsion whenever I realize I'm going to be hosting yet another copy of it.

Again, I think you're right, and it's not particularly meaningful to worry about the extra ~100 MB of space they're taking up (ALAC format), but it's an annoyance.

I wonder how often a bit exact copy of one song appears... Sure the songs might have the same title and duration, but some very trivial edits might be done. You need to be extra careful when identifying these songs as identical if you don't want to lose any information.

Of course, from a listener point of view it might not mean much, but how would you decide at which level of non-similarity a track is the same as another one?

It's a bit like choosing a lossy codec quality, it's very subjective, and for indexation this might not be the best way.

You bring up an interesting point: the identity function for a song is not self-evident. Even if two versions of a song are from the exact same recording and mastering, one could have a bit of extra silence at the end, or if they're lossy encodings, different encoders or bitrates would yield different files. What I said would only work with songs that are declared to be identical, however you choose to do that.

Each album is going to be mastered separately, and thus include slightly different tweaks (to volume, compression, whatever). You'll almost never see the exact same audio file stored twice.

It's fairly common in genre compilations and "best of" albums.

Those songs are identical in every pragmatically meaningful way, but they still won't be bitwise identical.

You'd have to do aural spectrum comparisons, with appropriate tolerances.

Which is why no one bothers.

Why do you care about this? When you listen to the album, you obviously want to hear every song on the album, and hard drives now are so big (and this occurence rare enough) that the extra space can hardly matter. So why do you care?

Obviously, it's not a huge problem. Like the author of this article, I am just annoyed at how difficult it is to conceive of and maintain a perfectly organized music collection. As for your specific question, however, it would be trivial to query your collection like SELECT * FROM songs WHERE song.album_id = 2, which would get all the songs on that album even if one of those songs is also part of album 3.

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