With very few exceptions, the average album has more filler than quality. It’s a downright tragedy that good CD space is so often wasted on mediocre interludes or self-plagiarizing repetition. But “In the Reins” is a wonderful exception to the rule. The seven-song EP is a gorgeous collaboration between the thoughtful and folky Iron & Wine and the eclectic Southwestern collective Calexico; it frankly defies expectation. There are no songs on the EP — better called a mini-album — that lack merit: Each is a joy to listen to. It is provides a melodious backdrop to pre-autumnal relaxation.

Sam Beam, the mastermind behind Iron & Wine, makes some of the most wonderfully soothing music today. He has lately gained mainstream popularity thanks to the “Garden State Soundtrack,” which features his lulling cover of the Postal Service’s “Such Great Heights,” but his previous two albums have proven his songwriting prowess.

Beam is no stranger to the EP. In February, the Floridian released “Woman King,” his most accomplished release to date, which found him experimenting with more vibrant and electrified music. “Woman King” is on the whole better than “In the Reins” — but to say that the latter is any short of fantastic would do it injustice. The true achievement here is the complementary addition of Calexico’s orchestration.

Calexico is less-known than Iron & Wine, but their career has been long and accomplished. A Tucson group centered around Joey Burns and John Convertino, the group has developed a reputation for interesting and original instrumentation, experimenting with their Southwestern sound by dipping into country, jazz and even a surf-rock aesthetic. On “Reins,” Calexico develops and enhances Beam’s sound, creating a partnership that is dynamic and sophisticated, greater than the sum of its parts.

The opener “He Lays In the Reins,” full of masterful harmonies and heartful lyrics, sets the tone for the rest of the disc: Chill, down-tempo, and soulfully bittersweet. Calexico’s touch becomes especially apparent when the emotive song is interrupted by mariachi singer Salvador Duran, who surprisingly steps in to belt the second verse in Spanish. The ardent addition works uniquely well on this track, elevating it to a level of unrestrained passion that Beam’s quiet vocals can’t fully achieve.

Hearing Beam and Burns sing together is a certain highlight of the mini-album. It’s strange that Burns refrains from taking any lead vocals, yet he does extremely well as a subtle backer for Beam on bridges and choruses. Because the latter rarely sings outside a single octave, Burns’s harmonies provide a beauty that Iron & Wine lacks. On “Sixteen, Maybe Less,” the harmonized chorus echoes nostalgia for young love. “I met my wife at a party when I drank too much./ My son is married and tells me we don’t talk enough,” they sing together. “Call it predictable, yesterday my dream was of you.”

“Prison on Route 41” is probably the track that would fit most comfortably within the intimate folk of an Iron & Wine record. But it’s Calexico’s wistful banjo, melancholy harmonica and trotting drum beat that give the song its flavorful dimension of Western authenticity. The song is so tranquil and smooth that the verses transition imperceptibly into delightful instrument solos.

The varied instrumental composition of the seven tracks provide a welcome diversity, best exemplified within “Red Dust” — the track with the least vocals and most creative orchestration. It begins with an addictive blues guitar riff, which is gradually sped up by an increasingly loud drum, unabashedly played over a funky electric organ and distorted electric guitar. Some listeners might think that the collaboration had reduced the two groups to a jam band, but there’s much more sophistication than whim. It’s a finely crafted groove that builds and ebbs around competing instruments without falling prey to chaos.

You are not likely to hear jazz trumpet solos on an Iron & Wine recording, and a longtime fan might not want to. But on “Burn That Broken Bed,” a serene trumpet — influenced by early Miles Davis? — supplements layered guitars to give a fuller effect to Beam’s quite lyricism.

The short album proves that less is more. From the mighty fusion of Sam Beam and Calexico, we get music with impeccable symmetry but unvarnished creativity. It is consistently impressive, even for listeners more accustomed to one band’s sound over the other’s, and only gets better with time. It’s the rare collaboration that you hope will happen again.