For this joint endeavour the artists exchanged a wealth of material derived from the inaudible sounds that are usually out of the frequency range for humans. Kubisch contributes electromagnetic recordings made while travelling through cities such as Montreal, Paris, Dortmund and Bangkok. Lockwood contributes a range of sources for her recordings which go from the earthly ultrasound of a Scots pine to massively sped up solar oscillations recorded from space! Just the list of sound sources puts this release into something of a class of its own. Each of the women have produced a piece based on their own material and then a second which is a mix of theirs and their collaborators sound sources.

The record's raison d'être, of capturing the life of the inaudible is an immediately fascinating and paradoxical proposition. If the sounds are outside of the frequency range for human beings how can they be used as the basis for a record? Conversely, if through scientific and studio techniques the inaudible is rendered audible, have they not obliterated the thing which they claim to be revealing? Certainly the unworldly and thoroughly unfamiliar sounds we hear on this record testify to their origin beyond the mundane. For every squeak, whoosh or throb on Lockwood's 30 minutes Wild Energy one wonders what the source was. A sudden rush of pure bass is overtaken by bubbling metallic sounds as if an alien species were trying to communicate though the speakers. What could the ultrasound of a Scots pine tree tell about the worlds that lie beneath the bark? Sometimes the sound seems to drop out entirely only to re-emerge from either the upper or lower range. There is a feeling of movement in the composition as if Lockwood was attempting to imbue something of the distance travelled, size or extent of time associated with some of her sources.

Lockwood's piece utilising Christina Kubisch's material Streaming, Swirling, Converging is a shorter affair but rich in texture and tonal counterpoint. To her own pan-global material she includes her collaborators fascinating electromagnetic recordings which bear some resemblance to modulated feedback. Both artists include some hydrophone derived material in the mix, which throws up the occasional gurgle or splash, enough to keep our feet on earth for the time being. The choice of material and sources is clearly important for Lockwood, ranging from the vast reaches of space to the inner life of a tree. The sounds here function like hieroglyphs pointing the way perhaps to some ineffable connectedness of all things. Ineffable, in agreement with the original inaudibility of her sounds.

Christina Kubisch's disk begins with Nine Magnetic Places a wonderfully layered piece deploying a range of recordings of electromagnetic waves composed - so the notes say - according the methodology of automatic writing. Collected on her travels across the world the materials for this piece testify to the traditional relationship between metropolitanism and the avant-garde of the early 20th century. It's a piece full of the buzzing (sometimes quite literally) of life, transit and intrigue, as throbbing bass drones open onto almost analogue synth-like tones and gradually modulating harmonics. Around the nine minute mark the fluctuating tones snarl up into a gravelly pulsating rhythm behind which another set of gloaming tones pulse in step. Fans of Nurse With Wound's Soliloquy for Lilith (which is also based on electromagnetic waves) or Pierre Henry's feedback derived work from the early 60s will lap this up.

The second longer piece titled Below Behind Above is the collaboration with Lockwood's sounds. The notes speak of how Kubisch was auditioning these sounds during two storms that tore through central Europe. The combination of the violent weather and Lockwood's interstellar material inspired a composition staging an encounter between different energies. In effect what we hear is a kind of hybrid between the two composer's use of these ultra and infra-sound materials. There's some nice use of effects that transform tonal vibrations into almost bird-like chirps. Indeed on this piece we hear the briefest hints of the phenomenal realm in sudden wood clunks, distant animals (heard as if from underwater) or the movement of water. Overall though this piece, like the others, still aims resolutely at the noumenal .

A fascinating collection of works of undoubted originality and quality, the question remains as to whether the "secret life of the inaudible" is really what they've managed to capture rather than a document testifying to the advances in audio recording and processing technology. Perhaps the key lies in the notion of a "secret life.." which implies the role of the composer as a kind of mystic initiated into an esoteric knowledge. Technology may obscure the object in itself, but to use a well known dictum from the history of mysticism that I hope the artists would not disapprove of; their subject matter is revealed in and through that concealment. The Secret Life of the Inaudible is a project at the cutting edge of sound art that poses questions as well as producing tremendous results.