ARP 2600 - Fundamental Concepts of Electronic Synthesis; Acoustical Waveforms and Electronic Generation

9
2.
TWO BASIC IDEAS
ARE
INVOLVED
in a!! electronic music
synthesizers.
2.1
THE
FIRST
is
that
ACOUSTICAL
WAVEFORMS
CAN BE GEN-
ERATED
AND MODIFIED PURELY BY ELECTRONIC MEANS.
2.1
1
Banging on
a
garbage
can
lid
generates a
horrible racket by
mechanical means.
The
racket
is
a
very complicated
sound;
but no mat
ter
how complicated it
gets,
it can be reproduced by a
single long
and
complicated wiggle
in
a
phonograph
record.
So
can
a symphony. From
a
certain point of
view
all
the sounds you've
ever heard,
ever will hear,
and
ever
could imagine, must
be
reducible
to
one
(or at most
two—one
for
each
ear) complicated
wiggle
of your eardrums.
2.1 1
1
Edison's phonograph
recorded
by
mechanical means the vibra-
tions
he fed into
it.
The
cylinder— and
later the disc—stored
them
as
mechanical wiggles
in a groove; on playback,
running
this
groove
past
a
needle made the needle wiggle,
the needle
made a
diaphragm
vibrate,
and the
diaphragm
passed it on to
the
air
in the form
of
pressure vibra-
tions, and the air transmitted the sound waves to somebody's ears.
2.1
1
2 Nobody
has
done it
that
way
for
quite a while
now.
Today,
a
microphone turns sound
waves
into electrical signals. In other words,
rapid
and
periodic fluctuations in air pressure are transformed into
rapid and periodic fluctuations in
some
electrical phenomenon— usualiy
a
voltage. In
this
form the
wave
can
be
electrically amplified,
equalized,
filtered, and subjected
to
various other indignities beforebeing sent
to
a
recording lathe that
turns
it
back
again
into a mechanical
waveform
in
a
groove. Likewise,
when
the
record is played, the stylus
wiggles
the way
it
did
in
Edison's player,
but its
vibrations are immediately turned into
electrical signals. They
don't
become mechanical again until they
reach
the
loudspeaker.
2.12
IN
ALL
THIS, THE ONLY THING
THAT DOESN'T
CHANGE
IS
THE SHAPE
OF
THE WAVE,
i.e. THE
WAVEFORM.
2.1 21
Suppose
you
bang an A-440
tuning
fork on the corner of the
table. In
1
/440th of
a
second,
then, the fork makes
one complete vibra-
tion back and
forth:
.
*
bOL0M+>
vosi&ori
cifr
reef-
forth
;
440-sec