Owner`s manual

CHAPTER 3 -
19
CHAPTER 3 -
The Craft of audio Synthesis
3.4.4
Signal Envelopes and Audible Event-Contours
One of the most fascinating areas of audio synthesis is listening for the envelopes of
time-varying events. Here there are all sorts of mysteries, in which signal attributes get
regularly “misperceived”: frequency variations get heard as volume, spectral evolutions
are heard as pitch, and amplitude envelopes generate an elusive spectral twitter.
3.5
Modules and Methods for Generating Signals
How can you get access to the signals and processes we’ve just described, so that you can
play with them on your own?
Throughout the past century people have been noodling around with electronic ways of
generating audio signals. In particular, beginning in the 1960’s, people such as Bob Moog,
Don Buchla, and Alan R. Pearlman began to settle on some ideas that have become
almost standard for audio synthesis:
independent, modular
functions for signal generation
independent, modular functions for signal generation independent, modular
and signal processing, capable of being controlled not only by hand but also by signals of
the same kind as they generate.
This was the idea of
voltage-controlled
operation, and it was completely revolutionary.
voltage-controlled operation, and it was completely revolutionary. voltage-controlled
Using independent, modular functions made it possible to change one attribute of a
signal without necessarily affecting any other attribute; so the craft of synthesis became
the craft of constructing, and tuning, integrated con gurations of modules.
The cables that connected modules were called
patchcords,
and so connecting modules
together came to referred to as
patching
them, and so,  nally, any working con guration
patching them, and so,  nally, any working con guration patching
came to be called a
patch.
Let’s take a look at some modules that generate signals.
3.5.1
Oscillators
A device that repeats the same
motion over and over is an
oscillator.
In audio synthesis,
oscillators typically produce very
simple geometrical-pattern signals
such as sine, triangle, pulse, and
sawtooth waves, named simply
for what their time-domain graphs
look like.
In an
analog
synthesizer, the
analog synthesizer, the analog
underlying medium in motion
is usually electrical pressure, or
voltage. In a
digital
synthesizer,
digital synthesizer, digital
the signal is actually generated as a sequence of calculated numbers. (Conventionally,
these are generated at the standard sampling rate for music CDs, 44.1KHz.) This does not
become motion until, at the output of the synthesizer, the number stream is converted
to variations in voltage, and then ampli ed, and then used to drive a loudspeaker. (A
loudspeaker is a motor that moves back and forth instead of around and around.)
Because oscillator-generated signals are periodic, their spectral components always form
a harmonic series.
9
Sawtooth
-3dB / Octave
Pulse
Triangle
Sine
Oscillator Output
TIME - domain
SPECTRUM
FREQUENCY - domain
t
f 2f 3f 4f 5
f 3f 5
f
10 136 7 8f 16f
f 2f 4f 8
f 12f 16f
1/t
OdB
-10
-20
OdB
OdB
-10
-20
-10
-20
OdB