Granulation of Sampled Sound

The technique I have found the most striking in the way it facilitates moving inside a sound is real-time granulation of sampled sound (Truax, 1990a, 1994b). Briefly, the technique divides the sound into short enveloped grains of 50 ms duration or less, and reproduces them in high densities ranging from several hundred to several thousand grains per second. A dramatic alteration of the sound called "time stretching" is made possible with this technique in that it allows a sound to be prolonged by any factor with no resultant change in pitch. The principle of the technique is that the samples within the grain are identical in order to those found in the original (hence the absence of pitch change), but the rate at which the grains move through the original material may be arbitrarily controlled. The fact that the grains are enveloped prevents audible transients and allows arbitrary sections of the original material to be juxtaposed and combined freely. The effect may be called "slow motion sound," as it was envisioned by filmmaker Jean Epstein in the 1940s, about the same time that physicist Dennis Gabor (1947) provided the theory about the grain as a "quantum" of sound appropriate to perceptual processing. However, granulation and its twin, granular synthesis, did not become a viable compositional tool until I was able to develop a real-time implementation in 1986 with a programmable digital signal processor (Truax, 1988) as part of the PODX system.

Since 1987 I have used this technique extensively to process sampled sound as compositional material (Truax, 1990b, 1992b, 1994b, 1996a, 1996b), at first being limited only to short "phonemic" fragments, as in The Wings of Nike (1987) and Tongues of Angels (1988). However, since 1990, longer sequences of environmental sound have been used in pieces such as Pacific (1990), Dominion (1991), Basilica (1992), Song of Songs (1992), Sequence of Later Heaven (1993), Sequence of Earlier Heaven (1998) and the opera Powers of Two (1995-99). In each of these works, the granulated material is time-stretched by various amounts and thereby produces a number of perceptual changes that seem to originate from within the sound.

Most obviously, the duration of the sound is usually much longer by anywhere from a doubling to a factor of several hundred times. This effect is used not merely to create drones, but to allow the inner timbral character of the sound to emerge and be observed, as if under a microscope. For instance, the crashing of waves in the "Ocean" movement of Pacific sounds remarkably like a choir of distant voices when stretched. The complex bell resonances in Basilica resemble organ clusters slowly dying away in a reverberant cathedral. However, in terms of the soundscape composition, the added duration also allows the sound to reverberate in the listener's memory, providing time for long-term memories and associations to surface. This effect was deliberately encouraged in the classically oriented soundscape piece Dominion, based like its predecessor, World Soundscape Project's Soundmarks of Canada on an east to west sequence of unique Canadian sound signals. By keeping the attack portion relatively intact and stretching only the body of the sound, each signal retained its recognizability, but allowed listening associations to be savoured, along with the inherent musicality of its constituent harmonics.

Secondly, the volume or perceived magnitude of the sound is enhanced by time stretching. Both the superposition of 10-12 asynchronous grain streams using the same material, and the prolonged duration, contribute to this effect. The resultant sound seems larger than life, and hence more potentially symbolic. In The Wings of Nike the enhancement corresponds to the heroic figure of the statue of the Winged Victory that is the basis of the accompanying graphic images, and in Tongues of Angels and Inside, the magnification of the instrumental sounds used by the soloist creates an environment that challenges his virtuosity (the pieces were written for oboeist Lawrence Cherney) while maintaining a fundamental timbral connection with the soloist. In terms of soundscape considerations, the magnification seems to relate less to the "brute force" amplification of the public address system than it does to the corporeality that is characteristic of acoustic sound.

I have used this sense of physical volume in Basilica to suggest a parallel between moving inside the bell sound and entering the volume of the church itself. In Dominion the enhanced sound signals threaten to overwhelm the 12 accompanying instrumentalists in much the same way that the vastness of Canada dwarfs the small population. However, the stretched sound also provides the pitches which the performers mimic, thereby giving them the role of personages within a landscape. In Pacific the sheer volume of some of the enhanced sounds suggests the vastness of the geographic region in question and the power of the ocean itself, though in the final movement, "Dragon," the stretched sounds of the drums, cymbals and firecrackers from the Chinese New Year celebrations mainly suggest a fiery mythical beast. The epic character of the forces and imagery in the I Ching cycle known as the Sequence of Later Heaven is suggested in my work of the same name which is based on chordal mixtures of four to ten Pacific Rim musical instrument sounds that are layered in up to 50 simultaneous grain streams spread out quadraphonically.

Thirdly, time stretching changes both the morphology (Smalley, 1986) and the associated imagery of the resultant sound. If it does so gradually, the listener may experience a process of transformation or interpolation (Smalley, 1993). The most extensive use of this feature may be found in my mixed media work Song of Songs, based on the sensual Song of Solomon text from the Bible. Time-shifting is used to modify the rhythm of the spoken text subtly and make it more songlike, as well as to prolong the sounds into sustained timbral textures, frequently accompanied by multiple pitch shifting implemented with a harmonizing technique. Although these sustained sounds are vocal in character, their length and steadiness mean that they resemble environmental sounds. Moreover, the amount of stretching was modified during the recording of the environmental soundtracks (birds, cicadas, crickets, monastery bells) in response to the vocal ones already present, thereby creating a constant interaction of all the material and further blurring the distinction between voice and environment. This sense of merging of sonic elements is consistent with the extended metaphor of the original text which compares the Beloved to the richness of the landscape and its fruits. At a time when the Western imperative to dominate Nature has reached a critical juncture, this metaphor of love would seem to offer an alternative image of the individual's role within the environment.

- Barry Truax

References:

De Poli, G., Piccialli, A. & Roads, C. (1991) Editors. Representations of Musical Signals. Cambridge, MA: The MIT Press

Gabor, D. (1947) Acoustical quanta and the theory of hearing. Nature, 159(4044), 591-594

Smalley, D. (1986) Spectro-morphology and structuring processes. In The Language of Electroacoustic Music, edited by S. Emmerson. London: Macmillan

Smalley, D. (1993) Defining transformations. Interface 22(4), 279-300

Truax, B. (1988) Real-time granular synthesis with a digital signal processor. Computer Music Journal, 12(2), 14-26

Truax, B. (1990a) Time shifting of sampled sound with a real-time granulation technique. In Proceedings of the 1990 International Computer Music Conference. San Francisco, CA: Computer Music Association

Truax, B. (1990b) Composing with real-time granular sound. Perspectives of New Music 28(2), 120-134

Truax, B. (1992a) Musical creativity and complexity at the threshold of the 21st century. Interface, 21(1), 29-42

Truax, B. (1992b) Composing with time-shifted environmental sound. Leonardo Music Journal, 2(1), 37-40

Truax, B. (1992c) Electroacoustic music and the soundscape: the inner and outer world. In Companion to Contemporary Musical Thought, edited by J. Paynter, T. Howell, R. Orton and P. Seymour. London: Routledge

Truax, B. (1994a) The inner and outer complexity of music. Perspectives of New Music, 32(1), 176-193

Truax, B. (1994b) Discovering inner complexity: Time-shifting and transposition with a real-time granulation technique. Computer Music Journal, 18(2), 38-48 (sound sheet examples in 18(1))

Truax, B. (1996a) Soundscape, Acoustic Communication & Environmental Sound Composition, Contemporary Music Review, 15(1), 49-65

Truax, B. (1996b) Sounds and Sources in Powers of Two: Towards a Contemporary Myth, Organised Sound, 1(1), 13-21