programming with max/msp - Virtual Sound

Chapter 3T - Noise generators, filters, and subtractive synthesis
> Filtered pseudo-random sample generators
In this kind of approach, the signal produced is filtered using a lowpass
filter. We will speak further of this kind of generator in the section
dedicated to lowpass filters.
INTERACTIVE EXAMPLE 3A – NOISE GENERATORS – PRESETS 1-4
OSCILLATORS AND OTHER SIGNAL GENERATORS
In Section 1.2T, we examined the “classic” waveforms that are often found
in synthesizers, such as the square wave, the sawtooth wave, and the triangle
wave. Section 2.1T explained how these waveforms, when geometrically perfect
(perfect squares, triangles, etc.), contain an infinite number of frequency components.
The presence of infinitely large numbers of components, however, causes
nasty problems when producing digital sound, since an audio interface cannot
reproduce frequencies above half of its sampling rate. 3 (We will discuss this topic
in much greater detail in Chapter 5.) When you attempt to digitally reproduce
a sound that contains component frequencies above the threshold for a given
audio interface, undesired components will appear, which are almost always
non-harmonic. To avoid this problem, band-limited oscillators are often used
in digital music. Such oscillators, which produce the classic waveforms, are built
so that their component frequencies never rise above half of the sampling rate.
The sounds generated by this kind of oscillator therefore make a good point of
departure for creating sonorities appropriate for filtering, and as a result, they are
the primary source of sound in synthesizers that focus on subtractive synthesis.
In Section 3.5 we will analyze the structure of a typical subtractive synthesizer.
It is, of course, also possible to perform subtractive synthesis using synthetic
sounds, rich in partials, that have been realized using other techniques such as
non-linear synthesis or physical modeling. We will cover these approaches in
following chapters.
FILTERING SAMPLED SOUNDS
Beyond subtractive synthesis, one of the everyday uses of filters and equalizers
is to modify sampled sounds. Unlike white noise, which contains all frequencies
at a constant amplitude, a sampled sound contains a limited number of
frequencies, and the amplitude relationships between components can vary
from sound to sound. It is therefore advisable, before filtering, to be conscious
of the frequency content of a sound to be processed.
3 It is for this reason that sampling rate of an audio interface is almost always more than twice the
maximum audible frequency for humans.
from “Electronic Music and Sound Design” Vol. 1 by Alessandro Cipriani and Maurizio Giri
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