USAGE
NOTES
In
general,
{he amount of expansion
to use is a matter
of taste. However,
some
guidelines
might prove useful as
you experiment with
different program mate-
ria] and
different
signal sources.
Classical
music,
for example, probably will
benefit most
from expansion at
the
lower
half (left
side) of the scale. You
might want to start
at 1.1:1 or
so
and range
from
1.05:1 to
1.25:1 for most classical
material. Using much
more than this may
make
a lot
of
classical
music surge
unnaturally, for usually
it has not
been se-
verely
compressed.
Popular
music, especially broadcast
over FM stations,
can use
much more
expansion
much of the time
—
say,
from 1.1:1 for material with
good dynamic
range
to 1.4:1 and above
for material whose
loudness levels hardly
differ. Some-
times
this music
gets so compressed that full expansion
by your dbx unit
won't
be enough,
really, but
improvements still will
be marked.
With
jazz you might want
to start somewhere between
these classical and
pop
settings, although
a quiet
and well-recorded small acoustic
combo won't need
much
expansion
at all.
Non-stereo-LP
sources (regardless of the
program) often
are badly constricted
in
dynamic range.
We mentioned
pop FM above, and
the same frequently is true
of video
signals, from VCRs,
video discs and cassettes, and
TV tuners and sta-
tion
transmissions in
the first place. Even classical music
in such media usually
sounds badly
squashed, and a 1.4:1 setting might
be the place to begin.
CAUTIONS
Any expander
can make greater demands of
your
power amplifier
and
loud-
speakers;
after all, that's its job. On the other
hand,
because
noise
—
rumble,
hiss, and
such
—
are reduced (expanded downward)
by an expander, the ampli-
fier
is being used more efficiently. Whether
a
given
amp is powerful enough
isn't
always easy to determine
after an expander is added, for it depends
on,
among other
things, loudspeaker sensitivity, the distortion
characteristics of the
amp, room
size, and
any
changes
in your listening-level habits.
Set for full expansion, the
4BX can
expand
a good recording to nearly 90 dB of
dynamic range,
and to realize fully such a range requires
a hefty
power
amp and
speakers
that can take high power. Fortunately,
such capacities in your compo-
nents
aren't essential for full enjoyment, and as we said in Usage Noles, more
often than
not you will be using your expander at
less than the
maximum,
1.5
setting and it will
be on music that
won't
stress your equipment.
The
point simply is that if your speakers and amplifiers
cannot handle the
widest
dynamic range
and the
expander
tries to drive them to that range, over-
driving
—
the excessive distortion of amp
clipping
and/or speaker
breakup
—
may be the result
at
the higher
sound levels. If this occurs with good speakers
and a
reasonably large
power amp, it probably will
be
noticed only with
pro-
gram
material
that has a good dynamic range
to begin
with,
music that actually
doesn't
need much expansion.
In
which
case what's called
for is
a
reduction in
the
expansion setting, not more-powerful
equipment.
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