It's easy to think of saxophonist John Butcher as working within a narrow audio palette, but in truth he's always pushing, restlessly pursuing directions previously unheard on his instrument. His experiments with microphone feedback in the last few years have been both beautiful and surprising, and in this duo with extended harpist Rhodri Davies he employs motors and what is billed as an "embedded harp speaker," which perhaps means a line from Davies in the bell of his horn. Or perhaps the other way around. Or maybe not.

For his part, Davies is no more beholden to the acoustic voice of his instrument. On these duets, recorded between 2007 and 2009, he uses pedal, lever and Aeolian electric harp, as well as his own embedded speakers. It's surprising how often over the course of the 45 minutes of Carliol the sound sources are complete mysteries and, likewise, how often they are obviously emanating from the vibrations of strings and reeds.

Which is not to paint the record as a guessing game or an illusionist's trickery. What is always the crux of minimalist music — from Satie to Feldman to AMM (and an argument could be made applying the condition to all music) — is the placement of auditory events, a craft at which Butcher and Davies are both masters. The sounds are what they are, they're sounds. But the arrangement of them is what makes Carliol a shockingly beautiful record. And while it ranks as one of the stronger recordings in either man's discography, it might not be entirely surprising to listeners familiar with those catalogues, at least until the final track. Butcher's soprano flutters nervously and incessantly over a gentle tone bed emanating from the amplified and wind-triggered strings of the Aeolian harp. It's an unusual tonality for both players, but also unusual in its construction, as it's the one piece not recorded live. In fact, more than 18 months separate the two instrumental tracks. Perhaps it's that separation or perhaps it's just projection based on knowledge of the separation, but there's an interesting disconnect in those final ten minutes.

The term "electro-acoustic music" is bandied about so much that any meaning based on syntax seems to be lost. It is used sometimes to refer to the acoustic properties of a performance space, other times to mean the combination of sorts of instruments. But so strong is the electro-acoustic element here that it deserves a new name. It is electronic elements placed squarely within the acoustic instrumentation. It is, let's say, bionic improv. And fantastically so.