How The Dbx Works - Tascam 688 Midistudio Owner's Manual

J
Be sure to concentrate while you are degaussing. Don't
try to hold a conversation or think of anything else but
the job you are doing. If the degausser is turned on or off
by accident while it is near the heads. you may put a
permanent magnetic charge on them that no amount of
car.eful degaussing will remove. You will have to get the
heads replaced. Make sure you are wide awake for this
job.
A clean and properly demagnetized tape recorder will
maintain its performance without any other attention for
quite a while. It won't ruin previously recorded material,
nor will getting it back to original specifications be
difficult.
I
CLEANING THE SURFACE OF THE 688
If the surface of the unit gets dirty. wipe the surface with
a soft cloth or use a diluted neutral cleaning fluid.
How the dbx works
Tho
DBX~
is a; wide-band
compression~)(pansion
system
which provides a net noise reduction (broadband. not just
hissl 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 employs RMS
level sensors to eliminate
compressor~xpander
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~mphasis
and de-emphasis are added
to the signal and RMS level sensors.
':800.=
~u~ ........
1
I
SUBSONICS AND INTERFERENCE
The DBX 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,
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.
-51 -