ARP 2600 - Audio Frequencies and Human Hearing Range; Understanding Frequency Ranges (Audio, Subsonic, Ultrasonic)

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to
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noise,
narrowband
noise,
noise centered around
2KHz, and
so on.
(See
also 2.182)
2.155 Each
of
these
waveforms,
at audio
frequencies, has its
own char-
acteristic sound
(see
2.13).
We
will not try to
describe
here the sound
of each waveform;
that
will
come into
your
own
experience
in
sections
4 and
5.
2.16 We
will
call
any
periodic waveform with
a
basic
frequency between
20Hz
and 20KHz
an
AUDIO WAVEFORM.
Frequencies
between these
two extremes are
AUDIO
FREQUENCIES. Higher
frequencies
are
ULTRA-SONIC
and
lower frequencies are SUB-SONIC,
or simply LOW.
2.161 Our reason for calling some frequencies
"audio*
1
is
of course
simply
that
only
vibrations
in
this
range can produce SOUNDS.
If
we
draw
a line and
put
"1
Hz"
in the
center
of
it,
and
let
the two
ends run
off to Infinity, and
let
every half-inch or so represent a
multiplication
by
1 or division
by
1
0,
then we get a
graph
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in which the range
of human hearing is
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2.162
OF
COURSE
YOU
CAN HEAR THINGS
HAPPENING AT
LOWER FREQUENCIES
than
20
Hz. BUT YOU
HEAR THEM AS
SEPARATE AND REPEATING SOUNDS, not as
continuing
tones
or
noises.
2.1621 Your heart is
beating,
let us
say, 60 times
per
minute.
(This
is
rather low for
a
pulse
rate
but keeps
the numbers simple.} That's
the
same
as
saying it
beats
once
every
second
and so we
can
say it
beats at
a FREQUENCY
of 1 Hz.
Let's draw
a
graph:
N
Now
imagine your pulse gradually
increasing
to 1 20
per minute, or
2Hz: