The one thing that I really miss both in iTunes and in the DJ applications that I’ve looked at so far is something that lets me easily organize and retrieve my music along a set of criteria, like e.g. energy level (low/medium/high), rhythm consistency, rhythm type, singers (male/female/both/none), genres (I know that there is a genre text box and has always been, but music genres are way more complex than that), etc.
Many software applications (e.g. blog engines, photo management apps, Finder, and also the Get Satisfaction platform that we’re using right here) have some kind of versatile tagging mechanism built-in. Not as in ID3 tags, but the kind of tags that you can attach e.g. to blog posts. I think that these tags could be very useful for music. For example, Uptown Funk might receive tags like energy:high, rhythm:straight, singer:male, genre:pop, genre:funk, popularity:top10. If I filtered my library using energy:high and popularity:top10, I would only see popular high-energy tracks.
I know that it is possible to simulate something like that using e.g. the Grouping field in iTunes, but tagging songs that way is really a pain in the ass. I also know that it is (very easily) possible to create this kind of structure using playlist folders (e.g. an “Energy” folder with three playlists in it), but if I want to find tracks that belong to two or more folders at the same time, I would have to go to iTunes, create a smart playlists for my current search, switch back to djay, and reload my iTunes library—that’s not something I want to do each time I’m looking for a song without knowing exactly which one I’m looking for.
So here’s my idea: What if you just added some Boolean logic to the track lists in djay so that we can select two or more playlists (e.g. using cmd+click) at the same time and then see exactly the tracks that belong to each of the selected playlists? This should be easy to use and easy to implement, without confusing anyone who doesn’t want to use that feature (because they simply don’t cmd-click their playlists).