For Mike Mangini, joining Dream Theater is clearly a dream come true. The 48-year-old virtuoso drummer can’t contain his enthusiasm when describing the reception he earned in Rome at his first live show with the standard-bearers for American progressive metal back in July.

“I don’t have the words to describe the magnitude of welcome I got,” Mangini declares, phoning from his Boston-area home. “When we stopped after the third song, they were chanting my name. And I didn’t know before the tour if I was going to get hit with a tomato off the forehead! It was a million miles beyond my expectations.”

It wasn’t just that his performance was a success, despite Mangini’s having had only one chance to rehearse the full two-hour set with his four bandmates. It’s also that he was replacing one of prog’s most revered skinsmen in Mike Portnoy, who cofounded Dream Theater in 1985 and helped create such epic signature tracks as “Pull Me Under” and “Under a Glass Moon” from 1992’s breakthrough Images and Words. No pressure or anything.

“I got a pile of [keyboardist] Jordan Rudess’s charts, because that’s really all I had,” says Mangini. “There were very few drum charts, and most of them were for songs we weren’t playing. I wanted to double-check the time signatures that I’m feeling versus the ones someone else might be feeling.”

Additionally, he tackled the challenge of adding drum parts to a new studio record whose music had already been composed: A Dramatic Turn of Events, which came out September 13. Superficially, this 77-minute effort seems relatively commercial. It’s less laden with 16th-note madness and blatant key changes than some Dream Theater outings, often feeling spiritually closer to 1997’s Falling Into Infinity or 2005’s Octavarium. Singer James LaBrie sets the tone with his carefully enunciated, dreamy reflectiveness on ballads like “This Is the Life”.

Yet, according to Mangini, who’s held several World’s Fastest Drummer competition records, technically focused musicians will still find much to love here. And that’s not just on polyrhythmic shred fests like “Outcry”, where Rudess, guitarist John Petrucci, and bassist John Myung trade off licks with astonishing dexterity.

“Don’t let your ears deceive you,” says Mangini. “For instance, ‘On the Backs of Angels’, the first single, doesn’t sound that difficult. But I’d put any drummer on this planet in a room for a week to see if they could play that. It’s wicked, because there are two parts happening at once.”

So Mangini will likely hear the sound of a metronome in his dreams, as Dream Theater’s tour plans stretch into 2012.

Dream Theater plays the Queen Elizabeth Theatre on Wednesday (September 28).