Cloud Formations

Curtis Roads is best known as the author of several landmark texts on computer music and as former editor of the prestigious Computer Music Journal (MIT

Curtis Roads is best known as the author of several landmark texts on computer music and as former editor of the prestigious Computer Music Journal (MIT Press). Fewer people, however, know Roads as a composer and software engineer. That could change with the recent release of Half Life, a new work available both as a standalone musical composition and as the musical component of a mixed-media (music and video) collaboration. Half Life is found on a new CD+DVD boxed set of Roads's music entitled Point Line Cloud (Asphodel, 2004).

Roads spent two years creating Half Life and describes it as portraying “a virtual world in which sounds are born and die in an instant or emerge in slow motion.” This description fits well with the synthesis approach Roads used, called pulsar synthesis — a technique that bears much in common with granular synthesis. After many years of research and experimentation in the area of creating music with minute segments of sound, Roads and collaborator Alberto de Campo developed pulsar synthesis and released software for the Mac called PulsarGenerator that employs the technique. PulsarGenerator is available for download at

Half Life is based on a 14-second sample that Roads synthesized using his own software. He applied a variety of techniques to manipulate the sample and used the results as the source material for the work. “Pulsar synthesis generates a train of sound particles,” Roads says. “Each pulsar particle repeats at a fundamental frequency with a formant peak in the spectrum above the fundamental. Depending on the fundamental frequency, one can produce either rhythms or tones. I controlled the fundamental and formant frequencies using separate time-varying envelopes that I drew on the screen.”

In Half Life, one hears a flurry of sonic gestures ranging from short, fluttering sounds to dense and colorful cloud-like clusters. The piece has an almost tactile quality, as if you could feel the different textures and surfaces. Roads applies meticulous control to each grain's spatial location, and though the work is presented in stereo on his CD, it is easily adapted to more complex sound systems. In fact, for its first live performance, Roads used 28 loudspeakers scattered around a large auditorium.

Roads isn't afraid to let chance play a role in his music. For the second part of Half Life, he created an algorithm to randomly select a unique center frequency for the filter on each grain. “At high-grain densities, this produced a texture in which up to several hundred independent filters were operating at any given second, leading to highly animated microtextures,” Roads says. Yet for Half Life's large-scale design, Roads worked on an intuitive level, even throwing out sections of music that didn't fit the grand scheme.

Roads thinks granular and pulsar synthesis have a huge potential for modern composers and sound designers. “Granulation can spawn a vast amount of output sound material from a tiny amount of input,” he says. “A given sound can be time-stretched by a factor of 100 or more. Along with this telescoping effect, other processes may also be occurring, such as pitch shifting, filtering, and spatial scattering. By shrinking the grain duration one can cause the sound to dissolve into broadband noise, and by varying the grain density one can play with the sound's transparency and mass.”

The existence of granular-synthesis features in many commercial and shareware programs — including Native Instruments Reaktor, Symbolic Sound's Kyma System, and Rasmus Ekman's Granulab — would seem to support his claim.

For more information, contact Curtis Roads;,