On the South Side of Iowa City, behind a little white house and through a thick door, Luke Tweedy sits in front of a screen of multicolored sliding bars. He’s in his editing room in early July, cleaning up a song he just recorded a triple-paned window away in his studio. A guitar and voice, sonorous and soulful, leap from two professional quality speakers flanking the computer.

William Elliott Whitmore leans forward in his chair. It’s his music that’s playing, and he’s trying to make sure every note sounds perfect. The two men, who are cousins, are finishing up some custom cover tracks they’ve been working on for XM Satellite Radio. The songs will be accompanied by the rest of Whitmore’s album, Field Songs, which will début July 12. This will hardly be the pair’s first collaboration; they’ve worked together for more than a decade.

“If he wasn’t doing that, I wouldn’t be doing this,” Tweedy said.

The 37-year-old is the founder, owner, and mastermind of Flat Black Studios. A sound engineer, he has worked with dozens of artists, including local folk group Milk and Eggs, whose first full-length album is set to be released Saturday. Tweedy has captured the lyrics and melodies of many bands as he has fine-tuned their sound.

But it all started with Whitmore.

One day in 1999, he came to Tweedy with a four-track full of music.

“I was pretty blown away,” Tweedy said. “I thought, OK, if this is going to be the deal with him, then I can help further that in my own way with my own set of talent, or if it’s not talent, then my forced skill set I developed.”

He invested in a standalone CD burner, and his music career was born.

Over the years, he has kept up with rapidly changing and improving technology.

“As I became dissatisfied with the way something sounded, I figured out ways to get past that,” Tweedy said. He learned techniques for recording — it took him years to re-create the foot-stomping sound he heard in his head. He trained himself to use new software — including Pro Tools, with its seemingly endless array of menus and digital knobs. He amassed tens of thousands of dollars of high-quality equipment — microphones, compressors, and amps. And he always asked himself, “What is the missing component?”

As he picked up new skills, he picked up new recording artists.

A few years ago, Tweedy met an aspiring musician named Zachary Lint at Record Collector. Lint had experimented with different genres: hip-hop, rap, rock and roll. He picked up a pseudonym — Coolzey — and joined Tweedy in the studio.

“He’s been just a great influence on my music,” Lint said. “When you’re recording with someone, there’s a fine line between their putting too much of themselves into a project or too little of themselves into a project. I really feel that he puts his mark on a lot of the songs he works with in a great way.”

Together, they’ve worked on about 10 projects. But many of Tweedy’s clients are newer to the studio. And while he picks out talent, he’s not picky about style. He’s worked with anyone from the soul band the Diplomats of Solid Sound to Joe Jack Talcum of the Dead Milkmen.

“It doesn’t matter what genre it is. If it’s quality, I like it,” Tweedy said. “Heart goes a long way. I can tell when somebody’s in the studio making a record if he’s going to be back.”

One 28-year-old with a penchant for writing love songs did return.

“Luke and I didn’t know each other,” Jordan Sellergren said about their meeting last fall. “But immediately, I felt really comfortable with him. It’s a lot like finding a therapist; you have to feel comfortable with him.”

Though the freelance graphic designer initially came to Tweedy as a solo artist, Sellergren soon brought her band, Milk and Eggs, into the studio. The folk group, with Sellergren and guitarist John Waite at its core, worked through the spring to produce its namesake first full album. Milk and Eggs will début Saturday digitally, on vinyl records, and on CDs. But while the compact disc was where it all started for Flat Black Studios, Tweedy is now prophesying its demise.

“CDs will cease to exist,” he said. “I’d be surprised if any label will still make them in a few years. There’s nothing a CD can do that digital can’t.”

But vinyl is a different story.

Not only does it still have the highest audio quality, Tweedy said, he said he thinks there will always be a “niche market” for the medium.

While the digitization has made music more affordable to audiences, artists have had to shift their focus, Tweedy said.

“Everything’s the means to an end, which is getting people to come to a live show,” he said. But it is time in the studio, Tweedy said, that proves the greatest financial hardship for musicians.

“Some of the bands that come here don’t have the time or the money to work in the studio for long periods of time,” he said. “A lot of bands here a have a hard time seeing hope.”

Often, Tweedy said, it can be difficult to manage a passion for music with the realities of insurance and water bills.

“There are different ways to define ‘making it,’ ” he said. “It can be making a little extra money on the back end to pay for rent or maybe making a comfortable living.”

He said he has made an effort to be more affordable than other studios in the area, but a day in a soundproofed room still runs to hundreds of dollars. And you can’t record an album in 24 hours.

No one knows those challenges better than a local artist Tweedy called “special” as he opened his iTunes and played a recently recorded track. Tweedy had to explain the melody was coming from a bass; it seemed too light, too quick, too melodic.

“It kind of bowls you over when you listen to it,” said Tyler Shoemaker, whose fingers are on the strings. “There’s these big big sounds, but they’re also really really fast.”

He’s 19, but his shoulder-length hair gives him the aura of a rocker from a different era. Fifth-grade band and private drum lessons introduced him to music. Shoemaker went through several more bands before he started working seriously on a solo project last summer. But while Shoemaker composes the parts, he can’t play them all. That’s where Tweedy came in.

“Everything was put together electronically,” Shoemaker said. “I had ideas of sounds that I wanted in my head and messing around with Garageband, I found a blend of sounds that was really pleasing to me.”

Tweedy helped him find musicians and, realizing that Shoemaker was paying for time in the studio by bagging groceries at Hy-Vee, adjusted his rates.

“He’s been instrumental in making my ideas happen,” Shoemaker said.

Tweedy swivels back in his chair, slips on a pair of headphones, and gives Whitmore’s track a final listen. Whitmore, who can’t seem to keep his guitar out of reach, plays a few riffs as he waits. It’s his simple description that seems to fit Tweedy best.

“He knows what sounds good,” Whitmore said. “That’s half the battle.”