dbx 4BX - Page 11

In
a high
fidelity
stereo
system,
the
highest
levels
that
can be
reached
likewise
are
determined
by
the
entire
system's
ability
to
play
the
loudest
parts
of
dhe
mu-
sic
without
distortion
becoming
objectionable.
Often
the
source
of
Ins
distor-
tion
is
tire
strained
amplifier(s)
and
loudspeakers,
but
it
may
come
from
the
record
player
and/or
stylus/cartridge
or
the
tape
deck,
and
frequently
it s
already
present
in
the
record,
tape,
or
broadcast
itself.
The
softest
sounds
in
a
performance
occur
just
after
the
musicians
stop
play-
ing
the
echo
and
reverberation
of
the
music
dying
out
in
the
hall
Surprisingly,
this
reverberance
may
still
be
heard
even
when
its
level
is
below
the
hall s
own
ambient
noise
-
the
ear has
a
remarkable
ability
to
pick
out
wanted
signals
in
the
presence
of
a
large
amount
of
(unwanted)
noise.
Nonetheless
a
convenient
and
conservative
figure
for
specifying
the
softest
sounds
practical
m
a
live
per-
formance
is
the
level of
background
noise
in
the
hall,
weighted
to
take
into ac-
count
the
ear's
decreased
sensitivity
to
low-level
(soft)
low-frequency
sounds.
The
true
peaks
generated
in a
live
performance
can
be
up to 115
dB
SI'L
for
a
full
orchestra
and
somewhat
higher
for
amplified
music.
A.
the
other
end
the
background
level
(correctly
weighted)
of a
quiet
ball
often
is
below
30
dB
SPL.
Tbe
difference,
then,
is
around
90
dB,
a
useful
figure
for
specifying
the
dynamic
range
of
live
unamplif
ied
music.
Unfortunately,
the
two
most
popular
forms
of
storing
recorded
music
that
are
currently
available
-
vinyl
analog
records
and
audio
cassettes
-
have
dynamic
ranges
much,
much
less
than
90 dB.
Conventional
records
do
well
to
reach
be-
yond
50-55 dD
of
dynamic
range;
the
most
carefully
prepared
"audiophile
pressings
may
have
slightly
over 65
dB
(provided
they're
no. decoded
discs,
which
upon
decoding
offer
more
than
90
dB
of
dynamic
range).
And
even
tbe
best
metal-tape
cassettes
cannot
reach
60
dB
on
their
own
without
.
,
noise-re
_
duction
system.
Clearly,
the
audio
signal
must
be
manipulated
in
order
to
fit
the
dynamic
range
of
live
music
into
the
constricted
limits
of
tbe
popular
storage
media.
This
manipulation
almost
invariably
is
accomplished
by
compressing
the
sig-
nal
and/or
riding
the
gain
in
the
recording
or
broadcast:
loud
passages
are
re-
duced
in
level
and
soft
passages
are
increased.
The
overall
dynamic
range
is
thereby
restricted.
More
than
30
dB
in
dynamic
range
has
to
be
gotten
r,d
of in
'The
wol.-kn.wn
Hctcher-Munson
curve,
for
single
.ones,
have
^^^^
ber of
researcher.
Among
Ihe
most
^^^^^^^^^^
demon*.*
Ih»
leaned
.sensitivity.
R*
example,
if a
2-kt
,
sound
,
mU
sic) a
HU
\
7
tone
has to be
at
about
1
15-dB
SPI.
to
sound
equally
loud,
a
deference
of
some
20
7a
'lower
levels,
the
difference
is
greater.
A
2-U
sound
at
60-dB
SPLtquiet
chamber
music)
el.
din
Ldnessby.SO-lfe^^
Z
sound as
loud).
A,
Lis
below
60-dn
SPL,
which
are
common
in
the
home,
the
relative
differ-
ences
are
greater,
Ml
we
remember
Iha,
.he
ear
can
bear
musical
,eve,be,a,lons
Iba,
lie
be.,,.,.
.*«|
^
Honed,
Iba!
many
recording
and
performance
slluallnns
are
considerably
qulele.
Iha
3MJ
S X
Ibeir
besl,
and
Iba,
background-noise
figures
lend
lo
be
aggregale,
nnl
.eadmgs
-
speclra.
it
become*
clear
Iha.
even
90 dB
of
dynamic
range
is
no,
enough.
I
lence
.he
need
for
d,g,l»l
recording
systems
of
110-dO
dynamic
range
(and up),
such as
Ihe
dbx
700
ser.es.