dbx 128 - FUNCTIONAL CALLOUTS; Front Panel Controls

FUNCTIONAL CALLOUTS
Fig. 1 — Front Panel Callouts
BELOW, ABOVE THRESHOLD (L.E.D.’s)
When the amber indicator is illuminated, the
input level to the 128 is below the threshold
level adjusted by the LEVEL control. When
the red indicator is illuminated, the input
level to the 128 is above the threshold level.
The L.E.D.’s do not measure output tevel.
DYNAMIC RANGE ENHANCER: PRE, POST
(switches} When the 128 is in TAPE mode and the
PRE switch is depressed, compression or expansion
takes place ahead of the tape recorder’s input (and
before tape noise reduction encoding if the 128
is in REC mode); when the POST switch is
depressed, compression or expansion takes place
after the tape machine's output (and after tape
noise reduction decoding if the 128 is in PLAY
mode). When the 128 is in DISC mode press the
POST switch.
PLAY LEVEL MATCH (control) Adjust
this control if the playback level from a
dbx I] encoded tape is considerably differ-
ent from the playback level of a non-
encoded tape played back in the bypass
PILOT (L.E.D.
indicator light)
Shows that the AC
power is ON
(illuminated), or
OFF (dark).
POWER (switch)
Controls the AC
power to the dbx
128. Push once
for ON, again
for OFF.
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NY
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DYNAMIC RANGE
ENHANCER
Lonoise reouction I
ABOVE THRESHOLD/LINEAR
(switch) In the LINEAR position
(switch in), the compression/
expansion section of the 128
operates in a normal fashion over
the entire program dynamic range
(see Figure 14 A & C). In the
ABOVE THRESHOLD position
(switch out), the compression/
expansion section acts only on
program levels that exceed the
threshold set by the LEVEL con-
trol (see Figure 14 B & D). This
changes the 128 into a peak limiter
(corresponding to COMPRESS
settings of the COMPRESS/EXPAND
control) or a peak unlimiter (cor-
responding to EXPAND settings of
the COMPRESS/EXPAND control).
Passages.
LEVEL (control) Sets the
“threshold’’ level above
which compression or ex-
pansion begins when the
ABOVE THRESHOLD/
LINEAR switch is in the
ABOVE THRESHOLD
position. When the ABOVE
THRESHOLD/LINEAR
switch is in the LINEAR
position, set the LEVEL
control so that ABOVE
THRESHOLD illuminates
during loud passages, and
BELOW THRESHOLD
illuminates during quiet
VANCE
COMPRESS/E XPAND (control)
Counterclockwise rotation of this
control past the 1.0 setting turns the
128 into a compressor with a ‘‘com-
Pression ratio” given by the numbers
on the surrounding scale.* Clockwise
rotation of the control past the 1.0
setting turns the 128 into an ex-
pander with an ‘expansion ratio”
given by the scale numbers.* When
the COMPRESS/EXPAND control is
set at the “1.0” setting (12 o'clock),
the 128 does not compress or
expand, and signals pass unchanged.
mode. The setting is not critical.
TAPE NOISE REDUCTION: REC, BYP, PLAY
(switches) When the REC switch is depressed, the
128's tape noise reduction circuitry is ready for
recording and encoding a tape with dbx {I tape
noise reduction. When the PLAY switch is de-
pressed, the 128's tape noise reduction circuitry
is ready for playback and decoding of an
encoded tape. When the BYP switch is depressed,
the 128's noise reduction circuitry is bypassed for
recording or playback of non-encoded tapes.
TAPE/dbx DISC (switch) Set this switch to
the DISC position, and press the PLAY
switch for playback of dbx II encoded discs.
The TAPE/dbx DISC switch should be in
the TAPE position for recording or play-
back of dbx II encoded tapes.
*The term “ratio,” whether associated with
“expansion” or “compression,” refers to the
amount of change in output /evel versus the input
level. A compression ratio of 2:1 (a COM-
PRESSION setting of 2.0) means that for a 2dB
change in input level there is a 1dB change in the
output level. An expansion ratio of 1:2 (an
EXPANSION setting of 2.0) means that for a
1dB change in input level there is a 2dB change
in the output level. A ratio of 1:1 (a setting of
7.0) suggests neither compression nor expansion,
so that for any change in input level there is a
corresponding change in the output level.