Music-comedy as we know it is a sham. Not that it’s less valid than other comedy — it’s just not music. Spinal Tap is funnier offstage than on, Weird Al only has one original tune and Adam Sandler’s fumbled guitar chords add little to his act.

They’re brilliant comedians and nothing more.

But fear not children, there is hope for the integrity of music-comedy in the hefty guitar-slinging duo known as Tenacious D. Jack Black and Kyle Gass could succeed in the distinct pursuits of laughter or harmony, but instead fuse the two in a bizarre celebration of the music industry, pot, German food, sodomy and, most importantly, rock and roll.

“The D,” as they revere themselves in their constant name-check shout-outs, was pigeonholed as a made-for-TV act following their short-lived HBO series. But the self-proclaimed “greatest band on earth” polished their odd routine at sold-out clubs across the country before the checks were cut for their appearances in “The Cable Guy,” “Bio-Dome” and “Mr. Show,” another HBO series.

This self-titled debut album succeeds in its lost genre because the songs stand up on their own. Their painfully funny power ballads could realistically be hits if fronted with the flaccid vocal stylings of Rob Thomas or Darius Rucker, your choice.

But let us not insult the D — it’s musically far superior to Hootie or Matchbox 20. The album serves up a coherent smorgasbord of Zeppelin’s bone-crunching hard-rock, Stevie Nicks’ mysticism, Skynrd’s power blues and the Tesla’s slow, feel-good metal.

Aside from the disheartening weirdness of everything that Black and Gass belt out in their full, Meatloaf-esque voices, the real humor of the D lies in their subtle joshing of musicians. They nail the sound of a band or era without stealing a riff. They sing about the absurdities of the style, but not in an outwardly funny way. In “Dio,” a tribute to spiritual cheese-rocker Ronnie James Dio, Black and Glass harmonize in an uber-serious monster ballad tone, “Your sauce will mix with ours, we’ll make a good goulash, baby!”

With a diverse supporting cast of Foo Fighter guitarist Dave Grohl, Phish keyboardist Page McConnel and producers the Dust Brothers, it’s easy for the D to jump into and poke around the soul of a genre. The guests fill out the duo’s “Devil Went Down to Georgia”-style epics, punctuating the knee-slapping storytelling breaks with spooky drones, polishing the transitions with smooth guitar licks and cool organ shrills. The disk reanimates all the D’s established favorites like “Kielbasa” (a funky ode to sausage and butt cheeks), “F— Her Gently” (a rare glimpse of the D’s soft side) and “Tribute” (a eulogy for “the greatest song in the world”).

In many ways, the Tenacious D album is groundbreaking. Beyond the obvious — the imaginative treatment of “motherf—er” and the first-ever comic usage of “buttress” — this album does more than just make you chuckle. Their potty mouths may mask their talent, but Black and Gass treat the album, first and foremost, as a musical creation. They constantly remind us that their goal is to rock out, which they do. The D has birthed the first true music-comedy album.