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GLOSSARY
Asperity Noise
This
is
a
swishing type
of
background
noise that
occurs with tape
recordings
in
the presence
of strong
low frequency
signals,
especially
when
there are
no
high
frequency
signals
to
mask
the
hiss.
Asperity
noise
is
caused by
minute
imperfections
in
the surface of the tape,
including variations
in
the
magnetic
particle size
in
the tape's
oxide
coating.
The
imperfections
increase or
decrease the strength
of
the
magnetic
field
passing the
play
head
in
a
random
manner,
resulting
in
audible
noise.
Asperity
noise
may
be
present
even
when
no
program
is
recorded.
When
a
program
is
recorded,
asperity noise
becomes superimposed on
the
signal,
creating
modulated
asperity
noise,
or
"modulation
noise."
Using
high-quality tape
with
a
calendered
surface helps
reduce
asperity
and modulation
noise
(calendered tape
is
pressed
smooth
by
high-pressure
rollers).
Attack
Time
Attack
time
may
mean
different
things,
depending
on
the
context.
In
music, the time
it
takes
for
a
note
to
reach
its
full
volume
is
the attack
time
of the note. Percussive
instruments have
short attack
times
(reach
maximum
volume
quickly)
and wind
instruments have long attack times
(reach
maximum
volume more
gradually).
When
a
compressor
(or
expander) changes
the
level
of
an incom-
ing
signal,
the
circuitry actually requires a
finite
amount
of
time
to
complete
that
change. This time
is
known
as the attack time.
More
precisely,
the attack time
is
the
interval (usually
measured
in milli-
seconds
or
microseconds) during
which
the
compressing
or
expand-
ing
amplifier
changes
its
gain
from
the
initial
value
to
63%
of the
final
value.
Aux
Input
(Aux
Level)
Aux
inputs,
an
abbreviation
for
auxiliary inputs, are
low
sensitivity
jacks
provided
on most
hi-fi
and
semi-professional
equipment.
Aux
inputs
(also
known
as
"aux
level"
or
"line level"
inputs)
have
"flat"
frequency response and
are
intended
to
be used
with
preamplified
signals.
Aux-level
(line-level)
signals
are
medium-
level,
higher than
microphone
levels,
but not
enough power
to
drive a speaker.
The
advantage
to these
levels
is
that
they are
less
susceptible to
hum
and
noise
than
are
microphone
levels.
Typical
items
which might
be
connected
to
aux
inputs are tape
machine
"play" outputs,
tuner outputs,
and
dbx
"play" outputs.
Mic-level
or
phono-level
signals
are
considerably lower
in level
than
aux
inputs
(approx. -60
to
-40dBV),
so they
will
not
produce adequate volume
when
connected
to
an
aux
input.
Moreover,
phono
cartridge
outputs
require
RIAA
equalization
which
is
not
provided by
aux
inputs.
Bandwidth
Bandwidth
refers
to the
"space"
between
two
specific
frequencies
which
are
upper and lower
limits;
alternately,
band-
width
refers
to the
absolute value
of the
range
of
frequencies
between
those
limits.
Thus,
a
filter
which
passes
frequencies
from
1
,000Hz
to
10,000Hz
may
be
said to
have
a
bandwidth
of
1
kHz-
10kHz,
or
it
may
be
said
to
have
a
9kHz
bandwidth (10kHz minus
1kHz
equals
9kHz).
Bandwidth
is
not
necessarily the
same
as
frequency
response.
Bandwidth
may
be
measured
at
low
levels,
and frequency
response
at
higher
levels.
Moreover,
bandwidth
may
refer
only
to
certain
portions
of the circuitry
within
a
piece
of
equipment, whereas
frequency response
may
refer to
the
overall
performance
of the
equipment.
Thus, while
the overall
input-to-output
frequency
response
of
dbx
type
II
equipment
is
20Hz
to
20kHz,
the band-
width
of
the
RMS
detection
circuitry
within
that
equipment
is
30Hz
to
10kHz.
Bass
The
low audio frequency
range
below
approximately
500Hz.
For
the
purpose
of discussion or analysis, the bass
range
may
be
further divided into
upper
bass
(250
to
500Hz),
mid
bass
(100-200Hz), low
bass
(50-100Hz), and
ultra-low bass
(20-50Hz).
Bass
Boost
An
accentuation
of the
lower audio frequencies
(bass
frequen-
cies).
whereby
they
are
made
louder than other frequencies.
Biamplif
ied
Descriptive of a
sound system which
utilizes a
low
level
cross-
over
network
to divide the full-spectrum
audio
signal into
low and
high
frequency
ranges.
These
ranges
are
then
fed to separate
power
amplifiers,
which
in
turn feed
low frequency
speakers
(woofers)
and
high
frequency
speakers
(tweeters).
Bias
Bias, as
the
term
is
used
in
tape recording,
is
a
very high
fre-
quency
signal
(usually
over
100kHz)
that
is
mixed
with
the
program
being
recorded
in
order
to
achieve
linear
magnetization
of
the
tape.
If
only
the
audio
program were
applied
to
the
recording
head,
a
very distorted recording
would
result
because lower-energy
portions
of the
program would
not be able
to
overcome
the
initial
magnetization threshold
of the tape
(known
as hysteresis).
The
frequency
of the
bias signal
is
not
critical,
so
long
as
the
record
and
erase
bias
are
synchronized.
However,
the bias
energy
level
has
a
direct effect
on
the
recorded
level,
background
noise,
and
the distortion.
It
is
sometimes
necessary
to
reset
the bias
level
for
optimum
performance
with
different
types
of
recording
tape,
and
professional tape
machines
are
equipped with
continu-
ously
variable bias controls;
many
consumer
tape
machines
are
now
equipped with
bias
selector
switches.
Clipping
Clipping
is
a very distorted
sound.
It
occurs
when
the
output
capabilities of
an amplifier
are
exceeded,
and
the
amp
can
no
longer
produce any
more
voltage, regardless of
how
much
additional gain
or
how much
more
input
signal
is
present. Clipping
is
relatively
easy
to
see
on
an
oscilliscope,
and
it
is
sometimes
audible
as
an
increase
in
harmonic
distortion.
In
severe cases of clipping (hard
clipping),sine-
waves
begin
to
resemble square waves,
and
the
sound
quality
is
very
poor. Often, the
maximum
output
level
of
an
amplifier
is
defined
as that
level
where
clipping begins
to
occur.
There
is
a
phenomenon
known
as
input
clipping,
and
this
may
occur
where
the input
signal
is
so high
in
level
that
it
exceeds
the level-handling
ability of
the
transformer
and/or
of the
input
amplifier.
Clipping
also
occurs
when
tape
is
saturated
by
excessive record
levels.
So-called "soft clipping"
is
usually the result of
transformer
saturation,
and
it
may
be
somewhat
less
objectionable
than
the
"hard
clipping"
that
occurs
when
output
voltage
limits
are
reached.
Aside
from
degrading
the
sound
quality, clipping
can
damage
loud-
speakers.
Output
clipping
may
be avoided
by
reducing
the
level
of
the
input
signal,
reducing
the gain of the amplifier, or using a
larger
amplifier.
Input clipping
may
be avoided
by
reducing
the
level
of
the
incoming
signal,
and
then
increasing the gain of the
amplifier.
Clipping Level
This
is
the
signal
level at
which
clipping
just
begins to occur.
Clipping
level
is
not always
easy
to
define.
It
may
be
a
matter
of
visually
judging the
waveform on
an
oscilliscope as
the
level
is
increased; alternately, clipping
level
may
be defined
as the
level at
which harmonic
distortion reaches a given value.
Tape
clipping, or
saturation,
is
defined
as the
3%
harmonic
distortion
level.
Compression
Compression
is
a process
whereby
the
dynamic
range
of
program
material
is
reduced.
In
other
words,
the difference
between
the
lowest
and
highest
audio
levels
is
"squeezed"
into a smaller
dynamic
range.
A
compressed
signal
has higher average
level,
and
therefore
may
have
more
apparent loudness than an
uncompressed
signal,
even
though
the
peaks
are
no
higher
in
level.
Compression
is
achieved with
a
compressor,
a special
type
of amplifier that
decreases
its
gain
as
the
level of
the
input
signal increases.
The
amount
of
compression
is
expressed
as
a
ratio
of the
input
dynamic
range
to the
output
dynamic
range; thus, a
compressor
that takes
a
program
input with
lOOdB
of
dynamic
range
and
yields
an output
program
of
50dB
dynamic
range
may
be
said to
have
a 2:1
com-
pression
ratio.
Compressor
A
compressor
is
an
amplifier that decreases
its
gain
as
the
level
of the
input
signal
increases to
reduce
the
dynamic
range
of the
program
(see
"compression").
A
compressor
may
operate over
the
entire
range
of input
levels,
or
it
may
operate only
on
signals
above
and/or
below
a given
level
(the
threshold
level).
Crossover
Frequency
In
loudspeaker systems
and
multi-amplifier
audio systems,
the
transition
frequency
(actually a
frequency
range)
between
bass
and
midrange
or
midrange and
treble
speakers
or amplifiers.
Crossover
Network
A
circuit
which
divides the
audio spectrum
into
two
or
more
frequency bands
for
distribution to different
speakers
(high
level
crossover) or different amplifiers
which
then
feed different
speakers (low
level
crossover).
High
level
crossovers are usually
built
into the
speaker
cabinet,
and
are passive
(they require
no power
supply).
Low
level
cross-
overs
are
used
in
biamplified or triamplified
sound
systems.
They
are usually self-contained,
and
come
before the
power
amplifiers.
Low
level
crossovers
may
be
passive or
active;
active
low
level
crossovers are
known
as
"electronic crossovers."
Damping
Factor
The
ratio of
loudspeaker
impedance
to the amplifier's
output
source
impedance.
Damping
describes the amplifier's
ability
to
prevent
unwanted,
residual
speaker
movement. The
higher the
numerical
value, the better the
damping.
DB
(Decibel)
also,
dBv
dBV
dB SPL
dBm
dB
One dB
is
the smallest
change
in
loudness
the
average
human
ear
can
detect.
OdB SPL
is
the threshold of
human
hearing
whereas
the
threshold of pain
is
between 120 and
1
30dB
SPL.
The term
dB
is
an
abbreviation
for decibel, or
1
/1
0
of
a Bel.
The
decibel
is
a
ratio,
not
an
absolute
number, and
is
used
to
express
the difference
between
two
power,
voltage or
sound
pressure
levels.
(dB
is
10
times
the
logarithm
of
a
power
ratio
or
20
times
the
logarithm
of a voltage