In this era, and from this distance, it’s become hard to tell if certain artists live in their computers or in impossibly strange cities. That confusion works to good effect here.

Two Bay Area bus line-themed mixtapes later (19 and 63), and I’m still working through the original. With 22 tracks, all loose, none irrelevant, 51 is ostensibly overstuffed but doesn’t play that way, eliminating any concern that Kool A.D. is overdoing it.

Dual is the mind that, when listening to the completed tracks of Duality’s first half, yearns to hear the dense productions without the dominating vocals, and then, when listening to the instrumental tracks of Duality’s second half, yearns for the vocals to return and smooth over all that dissonance.

The conversation begins, and continues, online:

GS: Have finally downloaded Rich Forever a year late, evisceration of my poor mind imminent?

[pause]

AM: Thoughts on the pulverizing immensity of Rich Forever? I remember listening to some luxury rap with you when I was in ABQ.

GS: It’s the finest music on the planet. Luxury rap sounds great in this land of no luxury.

[exit AM]

GS [to self]: “Keys to the Crib” whoa. Glad I waited a year and first heard it as ABQ offered another chance to walk under falling snow. GREAT walk to work.

Do I actually want to listen to music made by a 16-year old? Probably not, but that Chief Keef has the audacity/cause to name a mixtape Back from the Dead (and then follow it with an official debut called Finally Rich) proves he’s already lived pretty long. This is the weariest youth music ever, less than typically enlivened by the opportunities of music.

The most chaotic collection on this list, but also the most complete, in the way that a committed performer has to attend to all kinds of different things before taking the stage. So, we get Blanco’s first freestyle, plus a section of isolated vocal from Katy Perry’s “Teenage Dream”: Blanco creates Blanco, and considers the effect of pop music, not necessarily in that order.

Dark York was a bleary trawl inside someone else’s senses, and by that definition could’ve gone on as long as those senses continued to function (it nearly did). On Fly Zone, Le1f raps slightly above, rather than through, his environment, making this a more recognizable kind of music and a good excuse for less prolonged exposure.

Weirdly, perhaps unnecessarily, diverse for such a short release. Just as it seems Antwon will spend the whole album rapping over artfully decayed pop matter, the production switches gears, and the Notorious BIG comparisons he’s garnered start to make sense. He starts talking about back in the days as the album enters into a nostalgic, generous mode. But how generous? “It’ll All Make Sense” is barely a sketch, favoring transient mood over extended detail, so it’s hard to tell if its days refer to anything but some musical phantom of ’93. (And Biggie was not nostalgic for his own times, but for the real old days when lives were still whole; these culture loops start to get confusing.) So there are some problems here, but there’s also a thorough pleasure in the sounds. “3rd World Grrl” (odd appropriation of an old stylization of “girl”; also, the sexiest song on an album overrun with sex) should be all over the radio.

Electronic Dream was pure romance. This new very long set has time for more of that, and time to pollute it with an encroaching boring hedonism (upcoming Skrillex collaboration no anomaly). “This is for the ones who care,” some voice declares. That was always true, but you know the DJ’s pitching the latter if he feels the need to say that kind of thing.

Archie Moore (Black Tambourine, Velocity Girl, etc.) brainstorms unused Stereolab song titles (“Spectral Repair Kit,” “Mod Anagrams,” “Stylophony,” etc.) sets evocative music to them, adds unused Olivia Tremor Control artwork, and puts it online for free. But this is no idle work of an afternoon, but a survey of years, and yet with a consistent method: Not since the early days of The Magnetic Fields has a voice been so buried under such an overwhelming sensory world. What makes it a great mixtape is how all its weird symphonic digressions add up to a single idea of the universe of sound.