Grass Widow: From left: Raven Mahon, Hannah Lew and Lillian Maring. (Peter Hinson/PETER HINSON)

Perfect harmony seems effortless. In nature, it looks like orchids and bees, hummingbirds and butterflies, all practicing a mutualism based on jointly beneficial giving and receiving. In music, it sounds like bassist Hannah Lew, guitarist Raven Mahon and drummer Lillian Maring, members of the San Francisco-based band Grass Widow.

Over the trio’s stylistically evasive instrumentals — an often discordant lo-fi din that can shift from art-punk to surf music to Bond theme in a beat — all three constantly sing. There’s no spotlight-commanding frontwoman, no single principal songwriter, and the results are elaborate-yet-compact compositions that seem to change with each listen.

“I think that when we came together as a band, we realized that all three of us had something to say and something to express through the music,” Mahon said over the phone from New York. “It just made sense to make Grass Widow a project where that could happen equally.”

Sharing the work, not to mention the glory, might seem like a no-brainer, but it’s not always the norm. There’s a reason so many bands have a dominant voice; sometimes unilateral decisions are just more efficient.

“It’s been one of the most complex relationships of my life,” Maring said from her home in San Francisco. “[It’s] like being married to two women and doing everything together and putting that first. We basically live together for half of the year — in a car and in our crappy practice space.”

Grass Widow (Peter Hinson/PETER HINSON)

The women tackle inevitable disagreements with a constant dialogue. (“We’re overly communicative together,” Lew said with a laugh). And with so many words volleying back and forth, the group has found something that inseparable siblings might recognize — a common dialect that outsiders find esoteric. That idea of an idioglossia explains the name of the trio’s most recent album, “Internal Logic,” which is its third overall and the first full-length release on its own label, HLR.

“We’re really close and we’ve definitely been through a lot together,” Lew said. “We just kind of have our own language amongst us that comes out of that.”

Some of the group’s heavier memories during the past five years provided material for 2010 album, “Past Time.” Songwriting became therapy for Lew, who had lost her father, and Maring, whose boyfriend had cancer.

But the band found that catharsis can turn extreme. After touring the country, Europe and China, singing their sorrow night after night, the musicians opted to change course for “Internal Logic.”

“We were thinking, ‘Well, we’re going to tour this a lot, inevitably. Let’s make these songs as enjoyable to play as possible and just write lyrics that we want to sing to ourselves and to each other every night,’ ” Maring said. “So really positive affirmations.”

The album is defined by songs such as “Milo Minute” and “Whistling in the Dark” which are upbeat and playful, veering from lilting, minimalist indie-pop to the controlled chaos of screechy electric guitar freakouts. Meanwhile, “A Light in the Static” is a straightforward instrumental Spanish guitar track that keeps the mood serene.

Like most of the band’s decisions, the tonal shift wasn’t just about the music. It was a deliberate move to keep everyone happy in a bid for longevity.

“We’ve played in other bands where there wasn’t as much of an emphasis on everyone feeling good at all times, but that’s kind of what we’re always trying to do,” Lew said.

Right now that means turning Grass Widow into a less consuming venture. Between tour dates, the three are focusing on other projects, including Mahon’s woodworking, Lew’s filmmaking and Maring’s songwriting for other musical projects.

“I think a really important part of our sustainability is to have full-formed lives outside of the band as well as within the band,” Maring said. “To be honest and to be true to ourselves and to our own creative endeavors outside of the band will only help strengthen our relationships together and what we do together.”

Lew said the desire to maintain that balance could be a sign of age — “I think the older you get, the more you’re like, ‘I don’t want to do stuff I don’t want to do’ ” — and it extends to the band’s approach to touring. The women opt for two weeks on the road instead of five-week stints, so that they stay connected with friends and family.

“We take things into account,” 32-year-old Lew said. “Like, oh, maybe we shouldn’t drive all night and then play a show . . . Or, even though it costs more money to get a hotel room, maybe we should do that instead of sleeping on some 20-year-old’s floor. Because we want to stay a band longer.”

It takes constant tweaking to maintain the equilibrium, but the three agree the output warrants the effort. Balanced people make complementary bandmates, who make harmonious music. That’s a helpful lesson, and not just for musicians.

“This is really the longest committed relationship I’ve ever been in, and I’d say that it’s the most successful,” Maring said. “Everything we’ve been through together has taught me that it is possible to have that commitment to someone. And that’s affected my friendships, it’s affected all of my relationships. I’m really grateful for that.”

Grass Widow

9:30 p.m. Sunday. Comet Ping Pong, 5037 Connecticut Ave. NW. 202-364-0404. $10.