ARP 2600 - Circuitry Functions: Mixing, Filtering, Modulation; Waveform Mixing (Additive Synthesis)

12
Aec^y
attack'
2.17
Any low-frequency
waveform
may
be used to
produce events
and
to give
them
a shape.
But usually
a synthesizer will
have one
or
more
devices designed
specifically
to generate low-frequency wave-
shapes suitable for
giving events
a shape. These are
called ENVELOPE
GENERATORS
or
ENVELOPE
TRANSIENT
GENERATORS. Their
output
is
APERIODIC
(see
2.1422); instead of appearing over
and
over again
spontaneously
it
appears only when
the envelope generator
isTRIGGERED.
2.18 OTHER
CIRCUITRY in
any synthesizer
MODIFIES waveforms
by
MIXING
them,
FILTERING them,
or
MODULATING them.
2.181
Two
waveforms
can
be added
together
by
simply adding their
values
at
every
instant.
This is easier
to show
than
to talk about:
cltu^c
3
IOND->
OT-
-16Y
This
\y
added to this
'
makes this
.
Once
^
4-1
i^V^f
they are mixed
it's practically
impossible, except
in simple cases,
to
untangle
them again.
2.181
1
IT MAY SEEM
ODD
that
when
you have
mixed
together
say
the
sound
of
a
violin and
the
sound
of
a
piano (or
any
two or
more
instruments) it is all but impossible to separate
them again. But re- i I
AAA
/
member
what is going
on:
in electrical terms,
a
particular sound is
not
represented
simply
by "a voltage'' but
bv a PATTERN
of
voltage
fluc-
tuations.
So
when
two or
more signals are electronically mixed
into
one,
two or
more patterns
have
been
added
together
to
form a more
complicated pattern. And the
problem of
separating
them is not a
simple
problem of
dividing
a
voltage
into
little
voltages,
but
the
much more complicated one
of separating patterns, i.e.
wave-
forms, out
of one
complicated
pattern.
It
is
as
if
you
were to
copy
a page of this manual onto
one
line
by
writing
each
line directly on
top
of
the
preceding
line:
line
by
iwi^&iungv'eaehdiDepiyreqlkgaD^
all
the fetters would
be
there, but the
copy
would
be
illegible.
Your
ears,
from long
practice
perhaps, generally have no
difficulty
in
recognizing familiar patterns
in
the 24-hour-a-day
waveform
the
world
presents
to
them;
no other instrument can
even
begin
to ap-
proach
the ease
with
which, say,
you
disentangle the
voice
of
a
friend
A-
in a
crowd
from all
the other voices in the crowd. This is a
problem in
+1
^mMK
1
"