2. The Grain 
Like a nut, which has two basic elements, the shell, and the flesh contained within, a grain has an envelope which contains the actual sonic content. These two parts or parameters:
contents
make up an entire sonic grain. The sonic grain itself has a very short duration and as a single entity would seem very insignificant, but once the grain becomes part of a granular population, these two parameters make a big difference to the sound. Let us begin by looking at the contents.
The contents of the grain can be derived from any type of sound wave. The purest sound wave is the sine wave. The sine wave though, is not a natural wave, and it can only be produced synthetically. Barry Truax described it in such a way:
If you remember the first time you heard a sine wave oscillator your
ears should have told you this is not a good sound, this is not an interesting
musical sound. (Iwatake 1991)[1]
The main problem with sine
waves is that they theoretically have an infinite duration.[2]
The parameters of a sine wave allow the user to determine the frequency,
and the number of oscillations per second, but not how many seconds to
actually play the sine wave for (See figure 2.1). Using granular synthesis
the dimension of duration is added to the sine wave. By truncating the
sine wave it can technically no longer be called a sine wave. For better
understanding it may be called a sine grain (See figure 2.2).
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Fig 2.1: A portion of a sine wave
Fig 2.2: A sine grain (Dodge & Jerse 1997: 263)
Granular synthesis is not
limited to the support of additive synthesis techniques. Other forms of
synthesis can also be easily incorporated into the process. The contents
of the grain can for example be comprised of signals from any form of distortion
synthesis such as FM synthesis. The contents could also consist of white
noise which is generated using a random signal generator.
Sound samples are used often
in granular synthesis as grain contents. Before the technique of granular
synthesis was devised there was a technique by which sound samples were
broken into acoustical quanta as a means to stretch sound samples.[3]
This time stretching method involved breaking the sound sample into grain
sized acoustical quanta and then arranging them by overlapping quanta to
condense the sample, or by repeating quanta to stretch the sound sample.
This method alters the duration without altering the sense of pitch. It
can also be used to alter the sense of pitch without altering the duration
of the sample (Roads 1996a: 440-442).
There are two sorts of sampled
sound in granular synthesis. They are short samples, and long samples.
That may seem rhetorical but they are used differently. Short samples that
have the same duration as a single grain, can be used in their entirety
as the grain contents. A longer sound sample can be used in a series of
grains, although not necessarily in a particular order. The principle of
time-stretching has been carried over to granular synthesis which involves
a very deterministic progression of the sampled grains, but there are also
many other ways to use sampled sounds. These include using some grains
from a sound sample in the same way one would use a sine grain. For example
you might use just three small sections from a large sound sample as the
content source.
A sound sample is created
using an analogue to digital conversion (ADC) process.[4]
It can be represented graphically as such: (see figure 2.3)
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Fig 2.3: A digitally encoded sound sample
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Fig 2.4: The same sound sample after it has been formed into a grain
There are many different ways to create the contents for a grain. As more content ideas are introduced, the variety of granular textures increases. Looking at the sound sample after it has been turned into a grain it is obvious that the shape of the sound sample has changed. This is due to the introduction of the envelope, which will be discussed next.