For the past several months, musicians and performers around the country practiced multi-member compositions alone. But now that it’s April, the individual parts are harmonizing, and the musicians are ready to premiere the compositions to each other and to audience members of UC Santa Cruz’s 396-seat Music Center Recital Hall for the annual April in Santa Cruz Contemporary Music Festival.

“What all the musicians have in common is innovation — a commitment to making the music of contemporary composers, which is often experimental and challenging to perform,” said UCSC music professor and festival coordinator Benjamin Carson.

The annual festival takes place on six nights between April 4 and 18, with each night showcasing an eclectic performance or set of performances. This year’s concert series will feature the work of both local and international musicians, directors and composers.

Not only is the music technically challenging, but many of the musicians involved are from out of town, state or country. The rehearsal process is somewhat of a musical puzzle, coming together just in time for the audience.

“A typical concert takes about 6-9 hours of rehearsal to prepare, because the language we speak with each other is detailed and precise,” Carson said. “We learn our individual parts on our own, and then arrive at a distant city to finish the collaboration — polishing the sound and the rhythm and clarifying the way we interact.”

This will be the case when UCSC music professor Karlton Hester rehearses his intricate and ever-changing music. Hester’s performance will be like nothing the audience has heard before, quite literally, because randomness is one of the key musical components Hester works with.

“The music’s basis in spontaneous composition acts as a philosophical opportunity to use art as a means to examine the functions governing universal order,” Hester said.

When Hester takes the stage on the final night of the festival, after over a year of preparation, he will not be alone. His ensemble includes some musicians playing familiar instruments, like a violin, a guitar and a synthesizer. There are also some less traditional parts of the ensemble — a videographer, two people will play the waterphone — a steel acoustic instrument, and a poet and two dancers will perform Thai and African style dances.

“The most interesting aspect of this preparation will definitely come when everyone finally gets on stage to rehearse for the first time together on the afternoon of the April 18 performance,” Hester said.

This patchwork rehearsal process is not unique to Hester’s performance, nor does it sound remotely easy. Musicians must first individually master the technically dizzying compositions, then assemble the parts into an ensemble and finally perform the piece for an audience. A tall order for an even taller set of performers.

“Most of the performers are widely known in their fields, and some are internationally renowned,” Carson said.

The concert series is an opportunity to hear music one would not normally hear, and see performers one would not normally see — like San Francisco pianist Jeffrey LaDeur or El Paso poet Felicia Chamberlain. But the concert series is an opportunity for more than just the audience.

“One of the most important concerns for us is making sure we bring musicians here who are committed to mentoring our graduate students — either by performing their music or by delivering master classes while they’re here,” Carson said.

Pablo Rubio-Vargas is a first-year graduate student in UCSC’s Doctorate of Musical Arts program, and one of the many musicians contributing to the festival. He will premiere an original composition titled “Careless Storms,” which will be directed by Nicole Paiement, UCSC professor and artistic director of both the San Francisco Conservatory of Music’s New Music Ensemble and Ensemble Parallèle.

“I would describe ‘Careless Storms’ as different layers of sound moving to contrasting sonic textures,” Rubio-Vargas said. “Each individual instrument is helping build the different masses of sound.”

In spirit with the rest of the festival, Rubio-Vargas takes his inspiration from a number of seemingly incongruous musical traditions, saying he is inspired by Mexican folk music, electronic music, stochastic — or randomly generated music, and most heavily, chamber music.

So alas, after months of preparation, April is here — the moving parts are falling into place. Even though many of the musicians have never stepped foot in UCSC’s recital hall, the music is on the verge of its final stage.

“I need to refine the last stages of the piece, but my work is almost done,” Rubio-Vargas said. “Now it is time for the performers to present it as a concert.”