Jasmine Rosario and Lindsy Yi-Kennedy first launched the Original Soundtrack as an acoustic duo a little over two years ago with no real plan in mind. "Then it all fell in place without us really trying," said Rosario, 25.

Jasmine Rosario and Lindsy Yi-Kennedy first launched the Original Soundtrack as an acoustic duo a little over two years ago with no real plan in mind.

"Then it all fell in place without us really trying," said Rosario, 25, who will join fellow singer and guitarist Yi-Kennedy at Rumba Café on Saturday, March 12 for a concert celebrating the release of the now-quartet's debut EP (drummer Evan Carr and bassist Christopher Burris round out the current roster).

In the band's earliest days, Rosario and Yi-Kennedy shared little in common musically, save for a frustration with previous pursuits and a desire to create something that could have more of an impact. Rosario described herself as more of the rocker, which contrasted with Yi-Kennedy's more jazz-and-blues-oriented approach - traits that carried over into their respective demeanors in concert.

"I'm the one who goes crazy onstage," Rosario said, "and she's more calm, cool and collected."

Initially, these differences caused a natural friction, one which has dissipated almost entirely as the two have learned to work together.

"As friends we gelled instantly, but musically it was harder. It was more of a competition where we were butting heads, like, 'I want to be better than her and she wants to be better than me,'" Rosario said. "Then it slowly became more like, 'Man, she's there and I want to get there.' I use her as inspiration to get there, and then she uses me as inspiration to get here. We each want the other to get as high as they possibly can."

Rosario, in turn, has helped draw Yi-Kennedy further outside her shell onstage ("Before she wouldn't even look at the crowd, and now she's totally into it"), while taking away an understanding that it's necessary to dial things down on occasion.

"I've learned to back up a bit from her," Rosario said. "When you're onstage it's not about whose guitar is the loudest. It's about tuning in and listening and being able to create the best sound possible."

This ongoing learning curve has further informed and shaped the band's music, which still exists in a primordial state, in that it could evolve in virtually any direction moving forward (songs on the EP swing between jazzy, instrumental jams and swaggering blues-rock cuts like "Matchlight Girl").

"We're still learning how to have it sound like a cohesive band and not like, 'She's a lead singer, and I'm a lead singer, and it's a totally separate thing,'" said Rosario, who started playing guitar at age 12 and first performed publically at an open mike after turning 18 ("Before that I didn't think anyone wanted to hear me, or cared what I sounded like," she said). "Now it's like, 'On this song I might have more spotlight, and then on this song you're doing more of this.' There's more give and take, and that's what we've started working on."