Owner`s manual

20
CHAPTER 3 -
The Craft of audio Synthesis
CHAPTER 3 -
3.5.2
Noise Generators
A device that jiggles at random without ever repeating itself
is a
noise generator.
Waterfalls, steam, wind, fans, and such
things are all noise generators.
The spectrum of a noise signal is a statistical distribution
of frequency components. (This is the opposite of a sine
wave, which is exactly one frequency.) A noise spectrum
that is perfectly balanced throughout the musical range is
called
pink noise.
Pink noise is very useful in listening tests
of loudspeakers, because a trained human listener can hear
even tiny differences between two different noise spectra.
Filtering and equalization can shape a noise spectrum into
almost any sound.
3.5.3
Envelope Generators
A device whose output is intended to control some time-varying
attribute of an event is called an
envelope generator.
These are
sometimes referred to as transient generators, to call attention to
the fact that their output is not constant but transient.
An envelope generator produces an output signal only “on
demand”. The demand is made by means of timing signals called
gates,
and
triggers.
3.5.4
Sample & Hold Processors
The idea of “sampling” a signal does not directly relate to any particular characteristic of
audio events; instead, it is an idea from electronics that has turned out to be useful for
creating patterned control signals.
3.6
Modules and Methods for Processing/Modifying Signals
3.6.1
Inverters
A signal inverter works exactly like a seesaw. When the input goes high, the output goes
low, and vice versa. An analog inverter would output negative voltages on positive input;
a digital inverter simply multiplies its input number-stream by (-1).
White
noise
spectrum
Pink
noise
spectrum
Red (LF)
noise
spectrum
0dB
0dB
0dB
+15
-15
-15dB
-30dB
1 2 3 4 5 6 7 8
9
10
gate
trigger
ADSR
envelope
AR
envelope
envelope generators are controlled by gate
and trigger signals...