Demi Lovato, Nick Jonas headline Allstate Tuesday

Demi Lovato began her training in the dark arts of children's entertainment at a tender age - first as a disciple of the dinosaur, and later the mouse. At 7, she was singing on "Barney & Friends." At 15, she was starring in the Disney Channel musical "Camp Rock." Now, at 23, Lovato is a grown-up pop assassin whose stardom isn't quite super. Instead, she's a mysterious new master of the middle.

Lovato and Nick Jonas share a concert bill with special guest Mike Posner at 7 p.m. Tuesday, Aug. 2, at the Allstate Arena, 6920 N. Mannheim Road, Rosemont.

Unlike Disney graduates of yore (Justin Timberlake, Britney Spears, Christina Aguilera), Lovato and her ilk appear to be building their empires at a slightly different stratum of fame. You can hear Lovato all over the radio right now, along with her "Camp Rock" co-stars, Joe and Nick Jonas, and fellow former Barney-friend Selena Gomez. All four are true middle-masters of pop music - and while they don't always crack the top 10, it's not because their songs aren't good enough. It's because they're a very precise kind of good enough.

Middle-mastery is difficult to sniff out in a hit single. It smells like mediocrity, but it isn't. The music of a middle-master glows with personality, but not enough to make it seem exceptional. It can be risky, but never dangerous. Its pleasures feel big, but never totally euphoric, and its emotions feel genuine, but never completely cathartic. How does a pop song nestle itself into this perfect little no-place? That's a riddle only true middle-masters can answer.

It apparently comes more naturally to singers who began actively preparing for fame upon gaining sentience. These former kid stars don't always get to rise to the very top of the pops, but that means they'll never have to fall from the summit, either. Instead of burning superstar-bright, their careers might burn longer. And for showbiz kids who have been trained to nourish themselves with the roar of the crowd (and who are frequently dropped on their faces in the process), cultivating one's stardom in this aesthetic DMZ promises a sort of longevity.

Of all the middle-masters conquering our summer airwaves, Joe Jonas' new group, DNCE, currently ranks highest on the charts with "Cake by the Ocean," a disco-flavored hit whose nonsense lyrics include light splashes of profanity. (A middle-master knows how to deliver an F-bomb with the impact of a water balloon.) Little brother Nick is just two spots behind on the Hot 100 with his steamier ballad, "Close," while Gomez's "Kill Em With Kindness" works as a default motto for middle-mastery itself. (It's also more characteristic of the mode than her previous single, "Hands to Myself," a breathy tune with a surplus of charisma.)

Each of these pop stars, now in their mid-20s, are obviously much different from when we first encountered them in child-form, but it's strange how none of these songs feel like reinventions. That's because middle-masters don't re-create themselves. Their celebrity is a skillfully blended continuity - even in the case of frère Joe. With DNCE, he's playing down the family brand, but the music itself is still aimed directly at the kind of listener who grew up with the Jonas Brothers, then grew out of the Jonas Brothers - just like he did.

Nick was working on a similar balancing act last week in Washington during a concert with Lovato, where he delivered his very best songs with a countervailing shoddiness that veered on poetic; his falsetto went flat while singing, "I know we can get higher," and his diction went sloshy while crooning, "We've got champagne problems." The neutralizing energies felt abundant and mysterious. The guy seemed wholly determined to neither disappoint nor impress.

As for Lovato, her middle-mastery was very much a physical thing - she spent the entire night sleepwalking the stage while absolutely singing her face off. Her voice was at its most commanding throughout "Cool for the Summer," a year-old ode to same-sex kissing, and during the climax of "Without a Fight," a surprise duet with country star Brad Paisley. For a few minutes, Lovato had transformed the pop concert into a country concert without anyone really noticing. Maybe the middle is more flexible than it seems.

Also onstage that night, an even bigger surprise guest: Joe Jonas, who materialized for a "Camp Rock" reunion singalong of "This Is Me," a Demi-Joe duet about using your kid dreams to forge your adult identity. This was an undeniably sweet moment, but the instant it was over, Joe made the kind of pivot that doesn't actually exist in his career arc: "Now that we did all that sentimental bulls---, let's have some fun!"

On cue, the backing band strutted into "Cake by the Ocean," and the middle-masters smiled. They had just exploited their audience's childhood nostalgia, and now they were inviting them to dance away whatever shame may have surfaced in the process. Neat trick.

Of course, "Cake by the Ocean" will surely sound like sentimental manure someday - and the middle-masters will still walk among us without getting it on their shoes.