The official specification says:
The 'Lead artist(s)/Lead performer(s)/Soloist(s)/Performing group' is
used for the main artist(s). They are seperated with the "/"
character.
Or you can press ALT + T on your selected songs and add as many ARTIST entries as you need.
Mp3tag show them as \\Artist1\\Artist2\\Artist3\\Artist4 in the Tag Panel, but they are all saved in their own tags, all with the same ARTIST tag name.
Thanks, I guess this is correct then?
YOu may encounter different approaches to how players interpret fields with several pieces of data in them. Which means that there is no best practice.
On the other hand: try to find out for which purpose you need that separation most. If you do not really need separate fields but you can tolerate all pieces of data in 1 string, then go for the semicolon-space option. This shows you all the (e.g.) artists in 1 field and you don't have to fuss around with merging the fields if you want to write a new filename. Also, by avoiding any kind of slash (forward, backward, single, double) you do not run into trouble in respect to file system conventions and special characters.
And should it happen that you need a special separator, you can use MP3tag's functions to replace semicolon-space with that what you need.
See also here:
As @ohrenkino explains:
There is no "correct" or "best" way. There is only a "ideal way for you and your devices".
You will shoot yourself in the foot if you ignore your players or your different file systems. 
Hi,
Last weekend, I asked in this forum a couple of questions regarding multiple artists. I know that dealing with multiple artists is tricky, as you never know whether it's going to work in a particular music player. Unfortunately, I'm facing problems to create music libraries.
So far, I just add different ARTIST tags, one by one, and then, when I go back to the main screen, this is what I see:
Artist1\Artist2
Apparently, some music players don't support the double backlash as a separator, and only the semicolon works.
So, my question is whether the double blacklash is actually added at some point to store the information or whether it's just a way to indicate the user that there are two or more ARTIST tags and, deep down, there isn't really a double backlash.
If the double backlash is actually there, would it be possible to replace it with a semicolon without having to create an action? I like the approach of having a separate tag for each artist: it makes sense to me and it's tidy. I'm just worried that not all music players handle tags the same way. It could be an option under Settings: "Separator for multiple artists".
I could just stick to Musicbee, which is the only music player that has worked for me so far when dealing with multiple artists, but I wanted to make sure that I understand the problem and I wanted to try to find the best possible solution.
I hope it was OK for me to reopen an old thread.
I've just found this. I quote:
About the standards:
ID3v2 uses the "/" as separator between values
ID3v2.4 uses the null-characters as separator between values
Vorbis Comments (+ APE, +WMA, + MP4) has no separators and stores each value in separate file tag entry
Wherever you found that ...
Did you also have a look at th discussion in this thread?
And the best standard is worthless if the player of your choice does not support it.
You can always check in the extended tags dialogue whether you have real multi-value fields or a single field with separating characters in it.
I did read this thread, but at some point, with all the information I get from this and other sources, I don't know how to proceed further.
I would check: what does your favourite player show if you have real multi-value fields?
Do you see all the data or only the data from the first field?
If you see the all the data but the separator is a different one from the one in MP3tag, then you have to simply accept that and obey to the rules of the respective program. MP3tag shows the data with \\, other programs may show it with commas or semicolons or / or whatever.
The important thing is: do not enter data for multi-value fields in MP3tag in the way that the player displays it but always in the way that MP3tag needs it. The player will show it correctly.
If, on the other hand, the player only shows the data from the first field, then you have to join the multi-value fields to a single one and use the player's separator.
The linked thread features a list of how different players behave and which separator to use.
It really does depend on where you plan to use your music the most.
From my experience, using MusicBee on my PC and GoneMAD and Poweramp players on Android, I have to leave any files with multiple Artists with the semi-colon as the separator. This allows all three of these programs to show the different Artists as expected. Note that I have to maintain all edits from within mp3tag only. If any changes are made from within MusicBee, it automatically separates the tracks internally and this no longer works on other applications. I don't "reverse-sync" anything from my phone, so it wouldn't matter in those cases, but I avoid making updates on my devices out of habit.
To make things more interesting, I also use iTunes (for Windows) and have a few iPhone and AppleTV devices at home for the rest of the family that have no interest in Android (Boo!). In all cases here, the single Artist field remains to show with the semi-colon, as Apple has yet to support multiple tags. But at least a search for any Artist still shows a result this way.
As already confirmed, the double backslash \\ indicator in mp3tag is just that, a placeholder to show that multiple tags exist. This is not the same as using the semi-colon, or any other separator character(s), that may not actually cause the Artist fields to separate into multiple lines.
Thank you, @ohrenkino and @MotleyG, for your comments, and sorry for not replying earlier.
I needed time to process all the information and decide what to do next. In the meantime, AIMP now supports multiple artists the way they are implemented in mp3tag, and as I already checked that Musicbee works with multiple artists flawlessly, I think I'll just catalog my albums with multiple artists following mp3tag guidelines.
Hopefully, more and more software will support this feature over the time.
