ARP 2600 - Page 11

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2.14
THE TWO
SIMPLEST
RELATIONSHIPS
BETWEEN WAVE-
FORM-CHANGES
AND SOUND-CHANGES are
these:
2.141 Increasing
the
AMPLITUDE
of
an audio
waveform
increases
the
VOLUME of
the sound it makes.
(But it might
make no sound
at
all—
the
amplifier
might be turned
off or the
loudspeaker
disconnected.
The
point of
this joke
is to remind you that
electrical vibrations and
sound
waves are
not, after all,
the same
kind of activity;
there is
no
sound
inside
electronic organs,
or synthesizers
either. Sound doesn't
enter
into
the picture
at all until the rapidly fluctuating voltages which
the
organ or
synthesizer generates
are amplified and
fed
to
a
loud-
speaker.) (YOU
are interested
only in the
sounds—
but
the synthesizer
doesn't know
that.)
2.141
1
The
AMPLITUDE
of
a
waveform
is the
amount of maximum
deviation from its
"center". In
a
loudspeaker
this
"center" is the
posi-
tion
of the loudspeaker
cone at
rest; in
an
electrical circuit
h
"might be
a condition of zero
voltage.
The
amplitude of
a
loudspeaker cone's
motion
would
be
measured
in
inches or
more likely
in
fractions of
an
inch
back and
forth. The
amplitude of a fluctuating or alternating vol-
tage would be
measured in volts
positive and negative.
Thus a
voltage
waveform
that reached
a
peak
of +1
V and then
of
—1
V would
have
an
amplitude of
2 V "peak-to-peak".
2.1412 You'll save
yourself
a lot
of
confusion
by
thinking of AMPLI-
TUDE
only in connection
with waveforms
and of VOLUME only
in
2v
connection with
sounds. For example:
because
there are
no sounds
inside
a
synthesizer
(see
2.1
41
),
there cannot logically
be any
volume
controls;
but
there
are
a
great
many amplitude controls. The point of
our
putting so much
emphasis on this
distinction will
become clearer
as
you
read on.
2.142 Increasing the
FREQUENCY of an
audio
waveform increases
the PITCH of the
sound it makes. But it is
important
here,
just as with
AMPLITUDE and
VOLUME, to keep the
two
notions
distinct.
FREQUENCY
is
a
characteristic of
PHYSICAL VIBRATIONS (whether