He was emo before emo was cool. He was grunge, avant la lettre. J. Mascis and his band Dinosaur Jr. began thumping in 1983, which makes them contemporaries of R.E.M., U2, and Sonic Youth, even though most fans probably did not latch onto the records until the 1990s had kicked in — and the original trio had splintered, leaving Mr. Mascis, guitar visionary, to his own devices.

But the band pretty much forecasted everything that would rock in its underappreciated wake. Mr. Mascis, bassist Lou Barlow, and drummer Murph emerged from the sleepy scene around Amherst, Mass., to generate a cloudy mass of lo-fi turbulence, their anthems of slacker melancholy shot through with groggy confessions of inadequacy and white-hot guitar solos that crackled like lightning on a rainy afternoon.

Mr. Mascis’s emotional weather reports were always offered up in his trademark oxymoron of a voice, which was full of a passionate resignation. Especially on the band’s first three albums — “Dinosaur” (1985), the epic “You’re Living All Over Me” (1987), and “Bug” (1988) — the songs locked into a powerful formula that reveled in extreme contrast. Weary, sometimes mumbly vocals that expressed stoner angst over folksy strumming would alternate with explosive solos that evoked the sadness but also the restive urgency of Neil Young, circa “Cortez the Killer” — but punkier and noisier, which explained why the band was accepted in the American hardcore movement and became the template for Nirvana’s soft/loud/soft/louder dynamic.

Time and age have done little to temper Mr. Mascis’s vigor. Maybe the only thing more surprising than the 2005 reunion of the original Dinosaur Jr. lineup is how good its new comeback album sounds. “Beyond” (Fat Possum) is brawnier and more studiously produced than the band’s 1980s classics, and arrives as part of a logical sequence of events. Back in 2005, Merge Records reissued the early Dinosaur Jr. output in a newly remastered and extended editions.

Then the band did some touring, the deep and bitter rift between the notoriously aloof Mr. Mascis and the notoriously sensitive Mr. Barlow apparently healed, or healed enough for both to partake in the commercial benefits of a reconciliation. Ironically, perhaps, it was Mr. Barlow who enjoyed a momentary brush with mainstream success when the Folk Implosion, a side project to his post-Dino group Sebadoh, scored a Top 30 hit in 1995 with the song “Natural One,” written for the soundtrack to Larry Clark’s controversial film “Kids.” While both men enjoyed enough indie cachet on their own, the idea of a longerterm reunion obviously holds more allure than it used to.

In a weird way, guys like Mr. Mascis, who play from this particular songbook, represent to graying Generation X’ers what Frank Sinatra or Tony Bennett did to their parents and grandparents.

In which case, Mr. Mascis isn’t straying far from his archetypal course. He’s still doing it his way, even if his lyrics usually question what that way actually is. The first track off “Beyond” is nearly too obvious in picking up the ambivalent thread. It’s called “Almost Ready,” and in its fuzzy blur of stacked guitar lines you can take a stab at picking out the phrases Mr. Mascis sings in achy, but now somehow more cushiony voice: “Wondering if you missed me since / Wondering if I made a dent / Wondering what it is you meant …”

He could be talking to his fans, seeking some affirmation, or to Mr. Barlow, who once penned a tune called “The Freed Pig” after his acrimonious departure from the band. What’s more certain is the confident wallop of the rhythm section and the tidal surge of those guitars, over which Mr. Mascis solos as if hanging 10 on the wave’s crest.

There’s more variety to the album than this, although it’s easy to imagine how much fun such songs will generate on the summer festival circuit — and the challenge faced by 40-something fans trying to keep it real in the mosh pit without returning to the office with noticeable welts and bruises. The group has reimagined its sound in some surprising ways. Tracks such as “Pick Me Up” and “This Is All I Came To Do” compress the often shambling structure of two decades into shiny, riff-tastic tunes that play like classic — ahem, dinosaur — rock, with 1970s pop hooks and the multiple melodic and rhythmic shifts that marked FM radio fare in the days before XM and Sirius.

Along such lines, Mr. Mascis uncorks a meditative, quasi-acoustic ballad (see vintage Led Zeppelin), led by a gently strummed guitar figure, with Murph playing a stately parade rhythm in advance of a cello and the guitarist’s calm, nasal falsetto. “Can we be the same again?” he asks, perhaps begging the listener to read between the lines, then snapping the lull as a staccato blast of distortion introduces the next piece.

The answer, most certainly, is yes. Maybe even better.

Dinosaur Jr. will perform at Irving Plaza on June 6 & 7.