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Care and Maintenance How the dbx Works
Cleaning the Pinch Roller
Clean the pinch roller at least once each day the deck
is used. Use a good rubber cleaner.
1. Clean the pinch roller with a cotton swab
moistened with rubber cleaner, until there is no
visible residue on the pinch roller.
2. Using a clean cotton swab, wipe off all excess
rubber cleaner from the pinch roller. Make certain
that there is no foreign matter remaining on the
pinch roller.
Cleaning the Capstan Shaft
After cleaning the pinch roller, clean the capstan
shaft with a cotton swab moistened with head
cleaning fluid.
Degaussing the Tape Path
Hold the degausser about 1 m (3 feet) away from the
recorder. Turn it on, slowly move into the tape path.
Move the degausser slowly back and forth, touching
lightly all metal parts in the tape path. Slowly move it
away again to at least 1 m (3 feet) from the recorder
before turning it off.
CAUTION
If the surface of the unit gets dirty, wipe the
surface with a soft cloth or use a diluted
neutral cleaning fluid. Clean off thoroughly.
Do not use thinner, benzine, or alcohol, as
they may damage the surface of the unit.
Erase head
Record/Play head Pinch roller
Capstan
The dbx system is a wide-band compression-
expansion system which provides a net noise
reduction (broadband, not just hiss) of a little more
than 30 dB. In addition, the compression during
recording permits a net gain in tape headroom of
about 10 dB.
A compression factor of 2:1 is used before recording;
then, 1:2 expansion on reproduce. These
compression and expansion factors are linear in
decibels and allow the system to produce tape
recordings with over a 90 dB dynamic range – an
important feature, especially when you're making
live recordings. The dbx system employs RMS level
sensors to eliminate compressor-expander tracking
errors due to phase shifts in the tape recorder, and
provides excellent transient tracking capabilities.
To achieve a large reduction in audible tape hiss,
without danger of overload or high-frequency self-
erasure on the tape, frequency pre-emphasis and de-
emphasis are added to the signal and RMS level
sensors.
SUBSONICS AND INTERFERENCE
The dbx system incorporates an effective bandpass
filter. This filter suppresses undesirable subsonic
frequencies to keep them from introducing errors
into the encode or decode process. However, if
rumble from trains or trucks is picked up by your
microphone and fed to the dbx system, modulation
of the program material during low level passages
may occur. This low-frequency component will not
itself be passed through the recorder and so, will not
be present at reproduce for proper decoding. If this
low-level decoding error is encountered, and
subsonics are suspected, we suggest the addition of a
suitable high-pass filter in the microphone line.
80dB
Input
Dynamic range
of
input signal
Encoder
Tape deck
Decoder
Output
Encode
(Compress)
40dB 40dB
Record Playback
Decode
(Expand)
80dB
Saturation
level
+20dB
+10dB
+15dB
+25dB
+20dB
0dB
Dynamic range of tape
(65dB)
–60dB
–60dB
–30dB
–50dB
–80dB
Noise level
dbx encoding/decoding level diagram
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