The core of this is my respect, even reverence, for the sound itself. In the late 1960s, when I first had the opportunity to work with electronic sound, it was the ability to work with the sound itself, rather than the representations of sound in notated music, which was one of the great attractions. Another was the ability to move out of the prison of equal temperament, which seemed to me to be fundamentally anti-musical.

I began to form an ideal of sounds which could be taken on a journey of transformation, and for me transforming the sounds made by another musician became the key activity. In the 1970s this was very difficult, and I spent many years trying to develop systems that would make my dreams come true. It was not until the 1990s that the tools I needed began to become available. At that time I developed the basis of a real time digital transformation instrument, which became the Signal Processing Instrument - SPI - that I use today.

The crucial epiphany was the time I spent at STEIM in Amsterdam with Evan Parker in 1997, which is documented on our CD "Solar Wind" (Touch TO:35). This was the first time that a series of interesting concepts formed into something resembling a real instrument, the SPI. Of course there have been many developments since then, but the fundamental concept has remained the same. I am capturing the sound of my collaborator(s) and responding directly to their gestures with my own. They, of course, respond to my sounds, and the loop continues.

The nature of this is very interesting; on one level it is the same as the interaction between any two or more improvising musicians, the interplay of gesture and counter-gesture in a constantly varying continuum; but there is another layer of interactivity when the sounds of gesture and response are so deeply interwoven. Unlike many live processing performers, my instrument is not based on sampling technique, but on delay line technique; because the system is recording all the time, my responses can be very immediate, allowing very close relationships where gesture and response are like one entity, a "collective simultaneity" as one of my colleagues has described it.

At other times, because the short and long delays are part of the same structure, I can take a longer view, where the "now" and the "then" become confused in a complex mix of immediate responses and their multiple echoes. In describing the new instrument in 1998 I talked of a triangle of sound sources, those clearly originating from the source musician, those clearly emanating from the processing musician and a third category, sounds whose origin is no longer explicit. The important thing about this model, and a key characteristic of the SPI, is that these are not fixed points; I move freely between them without needing to cross boundaries from one to the other.

A key element of the SPI is the manipulation of musical time, and the Signal Processing Instrument might be likened to a kind of musical time machine: What is "musical time"? How does it behave? How is this "continuum of continua" perceived? Time is at the core of our understanding of the world; and memory is at the core of our understanding of time. Both are fundamental to our perception of music. What happens to this understanding when "artificial memory" interferes with our perceptions? In Borges's "Garden of Forking Paths" he imagines a Labyrinth of Time - "an infinite series of times, in a growing, dizzying net of divergent, convergent and parallel times", "...an enormous riddle, or parable, whose theme is time". Why does this concept seem so natural, and so musical? In his essay "A New Refutation of Time" he states, "I deny the existence of one single time, in which all things are linked as in a chain." Then later, "Time is a river which sweeps me along, but I am the river; it is a tiger which destroys me, but I am the tiger; it is a fire which consumes me, but I am the fire." What indeed is time? When and how is it "musical"?

Finally, I return to the opening theme, my respect for the sound itself; the same colleague has said: "You were always revealing some (even to me) hidden aspect of what I was doing, using me as a source but never reducing me to a mere resource. Conversely, I get the feeling that interacting with you, on the model that your approach demands, serves to reveal your performance as that of an autonomous instrumentalist rather than an extension of your sound source. As the process of mutual interaction unfolds we both reveal something of each other; I find we have opened up a space or a world where we co-exist, which can emerge to other listeners, who can also co-exist there. It's not the everyday world where we all began. When we return, things are somehow different, changed from when we left." (Adam Linson, excerpt from the liner notes to CD Integument, Psi 09.03)

Lawrence Casserley (last revised October, 2014)