ARP 2600 - Page 12

6
mechanical,
electrical,
or otherwise), but
PITCH is a
peculiar
charac-
teristic
of
THE
WAY HUMAN BEINGS PERCEIVE
physical vibrations
between
approximately
20Hz
and 20KHz. And
of
course
the whole
i
point of human
perception anyway is
to
register and
take
note of
changes in one's surroundings.
So a change in
an
audio
frequency
reg-
isters
as a
change in
pitch, but
frequency
and
pitch
are not the same.
2.1421
For
example: every
pitch
is produced by
some
frequency,
but
many
frequencies produce no sense of
pitch
at
all—because
they're
not
audio
frequencies. Middle
C
on a
piano corresponds
with a
fre-
quency
of
about 261 cycles per second—
but a
frequency of
2.61
cycles
per second
corresponds to no pitch
at
all—it
is
far
below
audibility.
2.14211 Here
is
some
useful
terminology.
Some
kinds
of vibration
have
a
repeating
pattern;
J
WV
and
if they do they
are called
PERIODIC.
One segment
of a periodic
vibration,
from any point in
its waveform to
the beginning
of
its
repetition,
is a CYCLE. The length of one cycle (usually stated
in
sec-
onds
or
in fractions
of
a second) is
the
PERIOD
of the waveform;
but
the
number
of cycles
occurring
in a given length of time
is the
FRE-
QUENCY
of
the vibration. There is an international standard
unit
of
frequency:
it is
the
HERTZ (abbreviated as
"Hz") and it is defined as
ONE
CYCLE
PER SECOND. As
usual, the prefix
"Kilo-"
means "one
thousand"
and
so a vibration
or
oscillation
of one
thousand
cycles per
second will
be
spoken of
as "One
KiloHertz" or
"1
KHz".
2.14212 NOT
ALL
WAVEFORMS are PERIODIC. Some
waveforms
happen
only
once;
and
some
waveforms are so complicated that your
chances
of
finding any
kind
of repetition are
nil
regardless
of
what
frequency
you
look
for.
In this case the
waveform
as
a
whole will show
no particular
repeating pattern
but
only
an apparently random motion.
For whatever reason, a waveform that does not
demonstrate any
re-
peating
patterns is
called
APERIODIC.
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2.5"
t
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