Coming into its fifteenth year, Aural Terrains is still going strong. Fields and Refrains, a collection of three modified solo pieces and one collective performance, is a case in point.

All works on this album are compositions by David Ryan, who does not personally appear on any of the tracks except as an assistant to the organist on the second track, “Overlays”. The scores, or recorded and augmented “grounds” to which the musicians must respond, are relatively loose, intended to create, to paraphrase Ryan, a dialogue with the soloist. (For more on the composition and performance process for each piece, see Ryan’s illuminating liner notes.) The result is a largely quiet set of performances, underneath which simmers a near-constant restiveness. The listener may anticipate but can never really know what will come next: a single tone, a short and soft cascade of notes, a strum or a woody pluck.

The first track, “Fields and Refrains”, is the longest, clocking in at over 23 minutes. Ryan wrote the score specifically with guitarist William Crosby in mind. It begins with spacious, understated rubbing and thuds. One hears a few plucks here and there after the first few minutes, which slowly fall into tones and at times feint a slow, disjointed melody. The scraping slows, then stops, as the plucks and knocks come into play together. Gradually, this turns, as the title hints, somewhat pastoral. Crosby begins to stretch from the non-idiomatic sounds to more standard notes, albeit without really settling on anything conventional. And, about halfway through, the piece coheres. The notes come in tighter clusters. The scrapes bleed into high plucks which merge into chords and a soft ever-emergent sweet melodic backdrop.

“Overlay”, performed by Luca Innocenti on organ (with a hand or two from Ryan himself) on organ, follows. This one will especially appeal to listeners who indulge in wide-eyed explorations of what tones layered on tones layered on tones can do. Pitches range and pile and collide. The piece ends with crisp five-note scales. At times, it sounds as if an ensemble of strings, winds and reeds are playing. At others, it sounds as if someone is really having a go at possibilities for elongation and perception-warping drones. That seems to be much of the point. This is maybe the least fluttery but most propulsive of the three solos captured here.

“Sanjo”, the next track, features Dominic Lash on bass and it is a minimalist, understated scorcher. It swings between slow and low arco and high sparse pizzicato. Lash is a musician of fastidious technique and of ideas. He avoids full melody in favor of full sounds, tonal decay, bends and frictions and atonal structures. The result is sad at times, as in when Lash approaches tuneful phrases, and is mysterious at others, most often when he avoids them. Always, however, the result is captivating. A fine show of what one can do with a contrabass, some modified playback and a lot of patience.

The final piece is a group effort and, at four minutes and twenty seconds, is the shortest piece by far. It is based on a recently reworked score, based on a 2007 work, which was inspired by the Edgar Allen Poe story Ligeia. As the most active piece, as well, and the only collaboration among all three musicians and the composer, “Ligeia 221” is a fitting, if brief culmination. Crosby, Innocenti and Lash each contribute long tones. Lash and Crosby also throw in some pizzicato and strumming that breaks up any potential monotony. In the end, these three musicians create a fuller sound — though not necessarily vision — than each achieved alone and work remarkably well towards a singular aesthetic through a range of techniques and sounds. Much of this could also be said of this entire album, which is a statement of some of the territory Aural Terrains has covered recently, as well as where acoustic-improv — more entrenched in new music than new thing — stands today.