A Brief History
The concept of a sonic grain or grain was first introduced by Dutch scientist Isaac Beekman in the early 1600's. The sonic grain concept can also been seen in the work of physiscist Denor Gabor (also the inventory of holography, or 3 dimensional photography.) Gabor introduced the idea of quantum sound, with the grain being the smallest, irreducable unit of sound.
Greek composer Iannis Xenakis was a pioneer of granular composition and his first work was created in 1971. The composition entitled "Analogique B", was created by splicing hundreds of vert small pieces of magnetic tape together.
Composer, educator, and author Curtis Roads moved the concept of granular synthesis from magnetic tape to the computer in the mid 1970s. Due to the primitive nature of computers at the time, the task of programming and generating computer based sounds was intensive and arduous. As technology improved, Roads continued to explore the world of granular synthesis. These explorations can be heard on works such as: Point Line Cloud (2005), Clang-Tint (1991-1994), Field (1981, Revised 1985), and nscor (1980, Revised 1986.)
What Is Granular Synthesis?
It is probably best to begin with a description of what a "grain" is. A grain is a tiny piece of sonic information (an audio sample) typically with a duration of 10 to 50 milliseconds. A grain consists of an envelope and the actual sound contained within the sample. The envelope removes the sharp edges of the grain by using an increase in volume (from no volume to a higher volume) at the beginning of the sample and a decrease in volume (from a higher volume to no volume) at the end of the sample. The envelope prevents clicks and distortion from being heard at the front and back of the sample. The sound of the grain can be derived from any audio material including various waveforms (sine, saw, square, triangle etc.) or from a recorded piece of audio.
Composing with Granular Synthesis
Granular composition, in it's basic form, entails arranging and layering grains of various speed, volume, and pitch over a given priod of time. Grains that are played back at very slow speeds are often refered to as "clouds." Grain clouds could be thought of as being a wash of sound, a sonic backdrop of sorts. Shorter grains tend to seem like they are front and center on the sonic canvas. They are bursts of sound that come and go very quickly and can be percieved as more rhythmic as a result.
http://www.granularsynthesis.com/hthesis/xenakis.html, http://www.sfu.ca/~truax/gran.html, http://www.granularsynthesis.com/guide.php, http://clang.mat.ucsb.edu/compositions.html