Getting there is half the fun, as the old saying goes, but the journey is really the whole point for Boston progressive-folk duo Tall Heights. Singer/guitarist Tim Harrington and singer/cellist Paul Wright know where they’ve been, and where they want to go. As for the route, well, “we’re just mapping it out as we take it, day by day,” says Harrington.

They’ve reached their biggest junction so far — Neptune, due August 19, is Tall Heights’ first album for Sony Music Masterworks, and the latest step in the ongoing evolution of their sound and style.

Harrington and Wright formed Tall Heights in 2010, keeping their songs stripped down to their essential elements, in part, to make it simpler to perform on the streets of Boston.

Neptune is a far lusher construct: along with pristine and emotive vocal harmonies, there’s subtly chugging electric guitar and a spare descending bassline on “Iron in the Fire,” ethereal synthesizers and a spacious drum part on “Spirit Cold,” a brittle splash of percussion to open “Backwards and Forwards” and feedback created by two cellphones on “Cross My Mind.”

“It was helpful and I think comforting to define ourselves as two vocalists, guitar and cello,” Wright says. “There was a beauty and a simplicity, and stepping outside of that box is pretty scary, because you’re forced to redefine yourself and do some sonic soul-searching. I think this record reflects the results of that scary step.”

The band’s broadening sound came from the musicians’ conscious effort to push themselves, and each other, to create in new ways. By relying on a few core elements at the start, the duo learned to make the most of their minimalist set-up. “It taught us to be lean and mean and effective with just two voices and two instruments,” Harrington says. “It made us consider vocal tone and the way voices can mesh and interact.”

As those lessons took root, the pair essentially gave themselves permission to push their musical boundaries outward over three separate recording sessions at Color Study studio in tiny Goshen, Vermont, that yielded songs for their 2015 EP Holding On, Holding Out, and for Neptune. Not only did Harrington and Wright expand their sonic palette throughout the process, they also altered their approach to writing. The musicians tend to develop ideas separately, before one brings a new song to the other for further development. It’s a reflection of their early days sharing musical ideas, when Wright was living overseas and Harrington was finishing up college.

“We would send each other terrible sound-recorder voice memo files and we’d write these nice emails to each other about each other’s songs, so creating concepts independently is something we’ve always done,” says Wright, who has been friends with Harrington since they were kids growing up in the central Massachusetts town of Sturbridge.

They changed the formula on Neptune. Four songs on the album — “River Wider,” “Infrared,” “Cross My Mind” and “Growing” — are the result of one musician looping a simple instrumental part and letting the other write lyrics for it. With the last recording session looming, the duo worked faster than usual on those songs, particularly the somber, atmospheric “Cross My Mind.” “We were under the gun, he was downstairs making one thing, I was upstairs making another thing, we put them together and then we workshopped it in the car on the drive up to the studio,” says Harrington, whose Boston apartment is literally upstairs from Wright’s.

Their ever-closer collaboration, and the time they gave themselves in the studio to develop it, is indicative of the band’s developing approach to making music. “I can hear the evolution happening,” Harrington says. “I feel like we’re walking across a bridge from one place to another, and maybe I’ll always feel that way, but I’m really happy with how we’re moving.”

“Intimate and arresting” – NPR

“Tall Heights employ a collection of acoustic guitar, cello, and electronic drums,​ ​reminiscent of contemporary indie folk giants like Justin Vernon and Fleet​ ​Foxes.”​​ – XPN

“In addition to finger-picked guitar, swelling cello and tight,​ ​prismatic vocal harmonies, ‘Spirit Cold’ boasts a bold, airy drum part​ ​that propels the song through the peaks and troughs of the​ ​arrangement.”​ – Wall Street Journal​

“It’s a contemporary sound that is not without its ageless qualities.” – Chicago Sun Times

“Certifiably unclassifiable” – Boston Herald

“There have been many bands in recent years that have employed beautiful close harmonies, but when you add the strings and the great songwriting, Tall Heights is a notch above the pack.”WBEZ

“Call it simply gorgeous.” – WFUV