dbx 161 Manuale di istruzioni - Pagina 13

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dbx 161 Manuale di istruzioni
Sub Harmonic
A
sub-multiple
of the
fundamental
frequency.
For example,
a
wave
the
frequency
of
which
is
half
the
fundamental frequency
of
another
wave
is
called
the
second sub
harmonic
of that
wave.
Sub Woofer
A
loudspeaker
made
specifically
to
reproduce
the
lowest
of
audio
frequencies, usually
between
20Hz
and 100Hz.
Synthesizer
An
ELECTRONIC MUSIC SYNTHESIZER
is
an audio
processor
that has a
built-in
sound
generator
(oscillator),
and
that
alters
the
envelope
of the
sound
with voltage controlled
circuitry.
Synthesizers
can produce
familiar
sounds and
serve
as
musical instruments,
or
they
can
create
many
unique sounds
and
effects of
their
own.
A
SUB
HARMONIC
SYNTHESIZER
is
a
device
which
is
not
used
to
create
music, but
to
enhance an
existing
audio program.
In
the case of the
dbx Model
100, the
unit creates a
new
signal
that
corresponds
to the
volume
of the
input
signal,
but
is
at
1/2 the
frequency
of the
input
signal.
Tape
Saturation
There
is
a
maximum
amount
of
energy
that
can be recorded
on
any
given
type
of
magnetic
tape.
When
a
recorder
"tries" to
record
more
energy, the
signals
become
distorted,
but
are
not recorded
at
any
higher
levels.
This
phenomenon
is
called
tape saturation
because
the
magnetic oxide
particles
of the
tape
are
literally
saturated
with energy
and
cannot
accept
any more
magnetization.
T.H.D.
(Total
Harmonic
Distortion) (See
"Harmonic
Distortion")
Threshold
Threshold
is
the
level at
which
a
compressor
or
limiter
ceases to
have
linear
gain,
and
begins
to
perform
its
gain-changing function
(i.e.,
where
the
output
level
no
longer
rises
and
falls
in
direct
proportion
to
the
input
level). In
most
systems, the threshold
is
a
point
above which
the
level
changes, although
there are
compressors
that
raise signal levels
below
a
threshold point.
Some
compander-
type noise reduction systems, such
as
Dolby,®' have upper
and
lower threshold
between which
the gain
changes;
these
systems
require careful
level
calibration for
proper
encode/decode
perfor-
mance. dbx
noise
reduction systems have
no
threshold
at
which
compression
or
expansion
factors
change, so
level
calibration
is
not
critical.
''Dolby'
is
a
trademark
of
Dolby®
Laboratories,
Inc.
Tracking
Accuracy
Tracking
refers
to the
ability of
one
circuit to
"follow"
the
changes
of
another
circuit.
When
two volume
controls are adjusted
in
exactly
the
same way,
the
corresponding "sameness"
of
the
output
levels
can
be expressed
as
the tracking
accuracy
of the
controls.
The
level
detection
circuitry
in
a
dbx
encoder
senses the
signal
level,
changes
the
gain,
and
creates
an
encoded
signal.
The
corre-
sponding "sameness"
of the original
signal
and
the
encoded/
decoded
signal
can be expressed
as
the tracking
accuracy
of
the
noise
reduction system, (dbx systems are
non-critical for the
operator,
and
are
built
to close tolerances, so that tracking
accuracy
is
excellent,
even
if
the
encoder and decoder
are
in
different pieces
of
dbx
equipment.)
Transition Level (See
Level
Match)
When
a
circuit
has
uniform compression
or
expansion
through-
out
its
full
dynamic
range, there
must
be
some
level
which
passes
through
the unit
without being
raised or
lowered (where
gain
is
unity).
This unity
gain
level
is
the
transition
level or
transition point.
The
transition
point
is
a
"window"
IdB
wide,
in
a
dbx
encoder
(compressor),
all
signals
above
the
transition
point
are
decreased
in
level,
and
all
signals
below
the point are increased
in level.
Con-
versely.
in
a
dbx
decoder
(expander),
all
signals
above
the
transition
point
are increased
in
level,
and
all
signals
below
the
point
are
decreased
in level.
The
transition
level
is
similar to
a
"threshold,"
except
it
does
not
refer
to a
point
at
which
compression
or
expansion
factors
change.
VIII
Triamplified
Similar to biamplified.
A
sound system where
a passive cross-
over
network
creates three
frequency
ranges,
and
feeds
three
power
amplifiers:
one
for bass,
one
for
mid.
and one
for
high frequencies.
The
amplifiers are
connected
directly to
the
woofers,
midrange
drivers
and
tweeters
without
a passive, high-level
crossover
network.
Tuner
A
unit
which
receives radio
broadcasts
and
converts
them
into
audio frequency
signals.
May
be
part of a receiver.
VCA
(Voltage Controlled Amplifier)
Traditionally, amplifiers
have been designed
to increase
signal
levels (to
provide
gain).
If
an
amplifier
were
required
to
decrease
the
level
(to
attenuate),
it
could
become
unstable,
and
might even
oscillate.
The
gain
(amount
of amplification)
in
these
traditional
amplifiers
would
be
adjusted
by one
of three
methods
(1
)
attenuat-
ing
the
audio
signal
fed to the
input
of the amplifier,
(2)
attenuating
the
audio output
of the amplifier, or (3)
changing
the negative feed-
back
(feeding
more
or
less
signal
from
the
output back
to the input,
but
in
reversed
polarity).
The
VCA
is
a special
type
of amplifier that
can be used
to
increase
or
decrease
levels
over
a
wide dynamic
range. Instead of
using
signal
attenuation or negative feedback,
the gain (or
loss)
is
adjusted
by
means
of
an
external
dc
control
voltage,
dbx
has
a
unique,
patented
VCA
design
that has
extremely low
noise
and
very
wide
dynamic
range; the
dbx
VCA
is
the heart
of
dbx
noise
reduction
equipment.
Woofer
A
loudspeaker
which
reproduces only
low
frequencies.