dbx 122 - Page 39

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DISCUSSION OF SPECIFICATIONS
Useful
dynamic
range,
in
the
dbx
122
and
124
specifica-
tions,
is
defined
as
the
difference
between
the
units’
weighted background noise and the peak signal encountered.
For both units the dynamic range is 110dB. How much of
this range your system is capable of recording and playing
back depends on the quality of your recorder and its
associated electronics. The specification implies a recorder
with
60dB
signal-to-noise
ratio
and
it
implies
that
the
dbx
RECORD
LEVEL
match
control{s})
have
been
accurately
adjusted.
For
a
recorder
having
a
45dB
minimum
signal-
to-noise ratio, it is possible to extend the signal-to-noise
to 70dB. :
Encode-decode frequency response also depends on
your
recorder.
Frequency
response
will
be
smoother
with
better recorders since the dbx noise reduction system tends
to multiply frequency response errors in a poor quality
tape recorder. The dbx unit itself is capable of 30Hz to
20kHz response, +1dB, and is within +0.5dB between
50Hz and 15kHz.
Encode-decode harmonic distortion consists primarily
of
low-frequency
third
harmonics
and
is
the
result
of
the
need
for
the
encoder
to
rapidly
track
changing
input
signal
levels.
At
very
low
frequencies,
the
system
may
track
sinusoidal inputs as if they were music envelopes. The
better
the
tape
recorder
low
frequency
response,
the
better
this
specification
will
be,
since
it
is
the
nature
of
the
dbx
noise
reduction
system
to
cancel
low
frequency
harmonic
distortion
on
playback
if
the
low
frequency
information
is
still present.
There
is
an
honest
question
about
the
importance
of
this
specification,
not
only
because
it
must
allow
for
un-
predictable
tape
recorder
non-linearities,
but
also
because
at
low-bass
frequencies
loudspeaker
distortion
may
reach
as
high
as
10
percent.
Above
about
200Hz,
the
dbx’s
harmonic
distortion
typically
is
less
than
0.1%.
The dbx 122 and 124 will produce 7 volts rms into a
5k-ohm
load.
Thus,
they
will
drive
the
inputs
of
several
high-impedance tape recorders at the same time.