Tascam TSR-8 - Understanding the dbx System; DBX Compression-Expansion Mechanism; Care and Maintenance; Tape Path Component Cleaning Guide

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How the dbx Works
TALE EN Ee
The
DBX
is
a
wide-band
compression-expansion
system
which
provides
a
net
noise
reduction
(broad-
band,
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
100
dB
dynamic
range
—
an
important
feature,
especially
when
you're
making
live
recordings.
The
DBX
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.
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Encoder
Tape
deck
Decoder
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TS
dbx
encoding/decoding
level
diagram
Noise
level
SUBSONICS AND INTERFERENCE
The
DBX
incorporates
an
effective
bandpass
filter.
This
filter
suppresses
undersirable
subsonic
frequencies
to
keep
them
from
introducting
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
fevel
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.
Care and Maintenance
OST
We
can’t
stress
the
importance.
of
cleaning
and
demagnetizing
too
much.
Oxide
shed
from
the
tape
and
accumulated
on
the
heads
and
other
components
in
the
tape
path
and
dust
or
debris
picked
up
from
the
air
can
result
in
poor
high
frequency
response.
Also,
the
heads
may
become
magnetized.
This
residual
magnetism
can
increase
noise
and
distortion,
significantly
degrading
record/reproduce
performance.
Clean
up
and
demagnet-
ize
at
least
every
day
before
you
start
to
work
with
the
TSR-8.
CLEANING
1.
Press
down
the
head
shield
to
get
full
access
to
the
heads.
2.
Apply
cleaner
to
a
coton
swab
or
lint-free
gauze
and
wipe
the
entire
surface
of
the
tape
path.
Wipe
off
any
excess
cleaning
fluid
with
a
dry
swab.
CAUTION:
Be
sure
to
use
a
good
cleaner.
We
remom-
mend
the
following:
TEAC
HC-1
(U.S.
only)
or
TZ-261A
(for
heads,
tape
guides,
guide
roller,
and
capstan
shaft);
and
TEAC
RC-1
(U.S.
only)
or
TZ-261B
(for
pinch
roller
and
counter
roller).
DEGAUSSING (DEMAGNETIZING)
A
little
stray
magnetism
can
become
quite
a
big
nuisance
in
tape
recording.
It
only
takes
a
small
amount
(.2
Gauss)
to
cause
trouble
on
the
record
head.
(Gauss
is
the
unit
used
to
measure
magnetism.)
A
little
more
than
that
(.7
Gauss)
will
start
to
erase
high
frequency
signals
on
previously
recorded
tapes.
You
can
see
that
it’s
worth
taking
the
trouble
to
degauss
regularly.
DEGAUSSING
IS
ALWAYS
DONE
WITH
THE
RECORDER
TURNED
OFF.
If
you
try
it
with
the
electronics
on,
the
current
pulses
produced
by
the
degausser
will
look
just
like
audio
signals
to
the
heads.
These
pulses
are
around
10,000
Gauss,
and
will
seriously
damage
the
electronics
and/or
meters.
Turn
off
your
TSR-8,
then
turn
on
the
degausser
at
least
1m
(3
feet)
away
from
the
recorder.
Be
certain
that
your
degausser
has
either
a
plastic
cover
or
plastic
tape
covering
the
tip.
Make
sure
that
no
metal
ever
touches
the
tape
heads
as
it
will
scar
them
and
ruin
them.
Slowly
move
in
to
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.
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
careful
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
specifica-
tions
be
difficult.
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