A well-studied second effort from San Fermin

Growing up in small-town Massachusetts, Ellis Ludwig-Leone lived in two worlds, studying classical piano by day and playing in high school rock bands at night.

After earning a music degree at Yale University, he melded those two disciplines in the bracing first San Fermin record in 2013, full of surprising flourishes of voices, baritone trombones, strings and his own classical piano.

The acclaim that followed a year of touring has resulted in a darker new album, "Jackrabbit," due out April 21 on Downtown Records.

Until then, an augmented San Fermin, with a string quartet and a pair of trombones as well as the core band of eight, is playing a series of concert hall dates - quite different from past shows at rock clubs and summer festivals.

San Fermin's blend of pop songs and chamber construction, out of the world of Sufjan Stevens or the National, grew out of the central dichotomy of creator Ludwig-Leone, who leaves the singing to longtime friend Allen Tate and new addition Charlene Kaye.

Over the phone from Brooklyn this month, Ludwig-Leone recalled a high school where he took classical piano but had a rock band. First a "terrible" heavy metal trio, he says, "with no singer and no bassist, then the pendulum swung the other way and I was in an acoustic cover band that played, like, 'Wonderwall' - you know, acoustic favorites of girls at parties."

He went to Yale with the intention of unlocking music's secrets. "I just felt at the end of high school I didn't know how music was put together," Ludwig-Leone says. "I could play through Ben Folds or Stevie Wonder songs or whatever, but I didn't really know how things functioned."

Not that he could spend much time on the rock side of his interests. "You learn to write in the classical tradition," he says. But he was putting together interesting concerts, including one that brought in the distinctive baritone of his friend Tate.

"It basically didn't work," Ludwig-Leone says. But in the process, he could start to see how it could.

After graduating, Ludwig-Leone went to a cabin in Banff, Alberta, to write what became the first San Fermin record, blending what he had learned about writing for classical instruments with writing rock songs for Tate's voice.

"It was like a big step forward when I realized that those two things could be in same room together," he says.

Of Tate, he says, "it's not only that his voice is so rich and great, it's also that he does serve as a kind of first editor for my stuff. I would have put a lot of goofier lyrics out in the world if he wasn't the one singing them."

The female voices of San Fermin, he says, "came up a little more accidentally."

After writing for Tate, "I basically wanted to put the other viewpoint out there."

A number of women have served as that singer, first Jess Wolfe and Holly Laessig of the band Lucius, then Rae Cassidy on the road and now Kaye (whose ethereal sound has been heard on Delta Airline boarding music).

Ludwig-Leone released the first sounds of San Fermin online, and when it got some buzz, he assembled a tiny concert in late 2012 "just to promote it, and see what happened."

He printed out his sheet music and hired more than a dozen musicians "with the promise of 30 bucks and one night of inconvenience."

The gig at Pianos on Manhattan's Lower East Side might have looked odd. "We were up there, I think, 15 of us at the time, reading off of sheet music," Ludwig-Leone says. "And somehow we got a record deal out of it."

In the eight months before their self-titled release was issued in September 2013, Ludwig-Leone had to solidify an actual functioning band that could tour.

"There was definitely some trimming down that we had to do," he says. "We had a glockenspiel player onstage for that show. Which was awesome, and we love her. But you can't afford to bring a second percussionist on tour if you're trying to fly to Europe.

"So I had to condense everything, which is really a good exercise for me, 'cause it was like, 'How do you make this really, really big music still sound big with only eight people instead of this larger group?'"

The band's name, taken from Pamplona's famous festival that features the running of the bulls, came relatively late, borrowed from the title of an interlude on the first album.

"I like the image of that," Ludwig-Leone says of the bull running. "Putting yourself in harm's way for seemingly no reason except for the thrill felt like the high-stakes thing I was looking for. And also sort of feels like performing."

The band spent a year touring, opening for the Irish band Villagers and playing a number of festivals.

Touring helped the band. "Seeing how music actually works live," he says, "rubbed off on the second record."

Most of the second album had been written during the lull between signing and release of the first album. But after the tour, Ludwig-Leone went in and tore the songs up.

"It just didn't quite feel right anymore," he says. "I think it felt like I was trying to replicate the first record when actually what I needed to do was adapt to the new life experiences that I'd had."

Ludwig-Leone described the resulting "Jackrabbit" as "a little darker, but it's also a little songier. There are less interludes, more songs that hit hard. On that first record, you'll have a pop song and then you'll have a rock song and then you'll have a weird interlude.

"On this one, all those things happen together, so it's less stylistically different from song to song; it's more one flavor," he says. "Which I'm happy about because it's the beginnings of finding the voice of the band."