Owner`s manual
12
CHAPTER 3 -
The Craft of audio Synthesis
CHAPTER 3 -
Another way to record such a signal is, with high-speed digital
circuits, to measure the underlying medium many times
each second, and store the measured numbers. This is
digital
recording.
Since the TimewARP 2600 is not constructed of electronic circuits,
concepts such as “voltage” don’t apply here. The TimewARP
2600 is software, a complex piece of computer behavior. The
signal medium for the original ARP 2600 was electrical pressure,
measured in volts. The signal medium for the TimewARP 2600 is
simply number sequences. We use those numbers the way the
original machine used electrical pressure; where the original
Owner’s Manual used the word “voltage” we will just say “signal”
o r
“signal level”, and in the module speci cations we will refer to
“virtual Volts” or “vV”.
3.2
Attributes of Signals
The simplest possible signal is a sine wave. It’s like the back-and-forth motion of a point
on a circle as the circle rotates. A lot of the mathematics of sine waves is based on that
rotating-circle idea; you don’t have to get involved in that unless you’re curious about
it, but it’s helpful to train your imagination by picturing the basic sine-wave graph as a
slightly stretched coil spring like a “slinky”.
The motion of a pendulum, or of a tuning fork, swinging back and forth as they slowly
come to rest, is a
decaying
sine wave.
decaying sine wave.decaying
A sine wave signal has exactly three attributes: its
frequency,
its
amplitude,
and its
phase
.
It has no other characteristics at all. (The decaying swing of the pendulum or the tuning
fork does have one other attribute: the amount of energy/amplitude that it loses on each
swing. It’s not a “pure” sine wave.)
3.2.1
Fundamental Attributes
Picture a point on that rotating
circle, leaving a trail behind as it
rotates, like an airplane propeller.
Picture the trail, stretched out
behind like a coil spring, and ask
yourself:
Analog signals @ 250 Hz
(approximately middle C)
A
B
C
D
E
F
G
H
I
forth
back
forth
back
in
out
higher
lower
higher
lower
up
down
north
south
positive
negative
forth
back
Source
Air Pressure
Wave
Microphone
Diaphram
Microphone
Output Signal
(Voltage)
Phonograph
LP groove
Magnetic
Field on Tape
Power amp
Output
(Volt * current = Power)
Loudspeaker
Cone
Your Eardrum
1
250
4 msec
=
amplitude
etc.
period
frequency =
period
1
( )
phase (important only
in comparing two signals)