One of the longest traditions in ECM's long history has been the improvised live studio session.

This date was captured as such in Lugano over three days in 2014.

Label head/producer Manfred Eicher suggested the collaboration, having enjoyed a radio program that offered an excerpt from a PUNKT festival performance by pianist Tigran Hamsayan and sampler Jan Bang.

The latter, Evind Aarset, and Arve Henriksen had all worked together on ECM before.

The music here was made as Hamsayan was preparing for Luys i Luso, an album of new choral arrangements of sacred Armenian music.

As one might expect given the cast and title, the two hours of music found on this double-length are drenched in textural and spatial subtleties (which is not to say there isn't drama -- check the dynamic knottiness on "Traces II").

Hamsayan's own preoccupation with Armenian music at the time (though he's always used it in his work) brings folk lyricism to the proceedings.

Bang, who's worked with many different kinds of musicians, is an expert in crafting mystery and otherness from what's on offer.

Aarset's skills with electronics have redefined the guitar's role in improvisational music.

Henriksen, a master of tone, texture, and melody, is a chameleon, as his many recordings as a solo artist and his collaborative projects attest.

His particular fondness for folk sounds is also on display here.

There are ten parts to the improvisation "Traces," interspersed with compositions by mystic priest/composer Komitas, whom Hamsayan brought in for interpretation on the spot.

Modern improvisation, ambient music, and the long legacy of Armenian traditional music all co-exist simultaneously.

On "Traces III," Henriksen makes his horn sound like a duduk (an Armenian oboe-like instrument) as Hamsayan explores minor Eastern modal scales.

"Traces V/Garun A" wanders into being via sculpted and sampled sounds, plucked piano strings and pedals, blurry, wafting guitar, and Henriksen articulating bits and pieces of a melody.

By the last third of its more than 12-minute duration, he's in the horn's high register and Hamsayan is offering blissful chords as Bang and Aarset color the spaces between.

"Traces VII" commences with angular trumpet and piano interplay as Aarset adds fragmentary chords and bent strings recalling Derek Bailey.

With Bang's samples and the crystalline upper register of the piano in the last half, it ends, seemingly, in another dimension.

Bang's presence is most clearly felt on the Komitas-closing medley "Angel of Girona/Qeler Tsoler," where his sampling -- processed and live -- sums up the entirety of the session's mystery as bandmates receive and comment on them.

The quartet's lack of a proper rhythm section on Atmospheres only adds to the speculative nature of the music; it makes for a demanding listen (at least in one sitting).

That said, it offers distinctive, illuminating, and abundant rewards to anyone who will encounter it on its own terms.