Evan Parker and John Butcher are, put simply, two of the very finest saxophonists of their respective generations (not quite a generation separates them, to be entirely pedantic). Each has developed his own, entirely sui generis technique, and both have been frequently imitated but rarely advanced upon. They remain the touchstones for reed players in the UK and further afield.

Psi is a label launched by Parker, and issue No. 1 is a set of solo improvisations recorded both before and during a concert at the now-defunct All Angels music night curated by Rhodri Davies. Never, it must be said, have I heard Parker sound so concentrated as on the first and longest of these tracks; it's a half-hour piece of continuous invention that virtually never strays from a single, simple, cyclical idea. By circular-breathing throughout, Parker creates a thick flow of sound and by using both multiphonics and quick alternations of large intervals he creates his familiar layered effect, with extremely high pitches dancing above circling mid-range clusters of notes.

The two concert tracks take the same approach. There is a freedom, of course, in playing in a lively acoustic to a small audience of fellow travelers, and one has the impression above all the Parker felt no compulsion to provide conventional openings into his music. Instead, he seems to be playing to please himself; while the beginnings and endings have more conventionally melodic features, the great central bulk of each piece is a wall of sound in which can be heard a dazzling quantity of music, but only for as long as the attention holds. Fortunately, this music is involving enough that, given a chance, it will keep you listening for its entire duration.

Parker's many recordings reveal a paradoxical player who has an instantly identifiable sound (or would, but for his imitators) but who plays a wide variety of music in an equally eclectic range of settings. Here we get not the "true" Parker, but a very different one from the one that emerges from his duets and small group projects. Superficially, at least, much more spiky than I have heard Parker sound, this will excite and intrigue fans, although newcomers to his music might be put off.

Butcher's music springs from the free improv experiments of the players of Parker's generation, but in no way does it sound as if it derives from the older man's approach. Whereas Parker has his roots in free jazz, Butcher is associated with New Music and, although not (to my knowledge) either a composer or performer in that field, his style is unmistakably allied to it.

Like Parker, his palette contains sounds which the average sax player didn't even know where in the instrument. Unlike Parker, however, he rarely contextualises these sounds with more conventional articulations. Instead, his vocabulary seems to be entirely made up of multiphonics, squeaks and extreme articulations.

As a solo performer, Butcher is compelling; in duet -- a format he has favoured of late, if recent releases are anything to go by -- his ability to function depends largely on the degree of comprehension he receives from his partner. Fortunately, Gerry Hemmingway works well with him, particularly on unpitched percussion. One wonders what he was really thinking when he picked up the harmonica for the relatively brief "Hay," but it actually turns out nicely enough, although more than one such piece would probably have been a mistake.

As for his midi-triggered sampler, this is something of a pleasant surprise. Such things generally mean either (a) mindless parrotting of what's just been played, or (b) the facility to trigger predetermined inappropriate noises. In Hemmingway's hands, however, it becomes a reasonably organic part of the duo, and the track "End of Cane Cloud," which features the instrument quite heavily, seems to disembody and transform Hemmingways percussion setup without crudely making itself stand out.

"Jackpot" is the track that provides perhaps the most familiar picture of Butcher's music-making; the rest of this album is very much a duet, as much the percussionist's as the horn player's. Some of it can sound a bit rarified; that's part of the deal with this kind of music. Both men have done more dramatic things elsewhere, but here they seem to liberate one another from any need to be flashy or theatrical, and their musical conceptions turn out to be either surprisingly similar or impressively able to cleave together without the loss of individuality.