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obvious but are interesting.
The first notable effect
is that
the recovered left
and right channels
will not necessarily
be
well
peak
limited.
For
this
reason, FM
stereo broadcasting
cannot
fully
utilize
this type
of
limiting
without serious
overmodulation
difficulties.
(Due
to
the
modulatiori vector
summation of all
signal components in
the FM stereo
multiplex
signal, it
is necessary
to limit
the discrete
left and right
channels to properly control modulation.)
Another
result
of matrixed
limiting
is that
the stereo
separation may become greatly
enhanced if the limiters
are not
opera ted in
"Tracking" mode.
This is
because the
di f ference
component, which is usually small compared to the sum component,
can
achieve
higher
relative
signal
level
through
separate
limiting.
The
effect
is
usually
desirable
for
AM
stereo
transmission, because increasing the relative difference
energy
level
does
not reduce
the
monaural amplitude
modulation and
improves the stereo signal-to-noise ratio.
In this case, the AM
radio listener who switches his receiver to stereo mode or tunes
from a
mono station
to a
stereo station
with a
stereo tuner
hears the
stereo signal
become louder,
with the
center audio
approximately
as
loud
as
the previous
mono
audio
but with
significant
additional
left
and
right
audio
level.
The
"hole-in-the-middle
I'
effect produced
by this type
of opera t ion
is usually
not noticed
since the
center is
not perceived
to
diminish as much as the sides are perceived to increase.
It should be noted that
if
the Studio Dominator is
placed
in
"Tracking"
mode,
the
sum
and difference
information will
always
remain
in
normal
proportions,
and
therefore
the
de-matrixed stereo will not obtain enhanced separation
.
The sum
signal, being usually
the greater in
level, will thus
control
the gain reduction of both the sum and difference channels.
In
the unlikely case that the difference channel should contain the
greater signal, the sum
channel will track the
difference, and
thereby remain
in normal
proportion.
Operating
in this
mode
will not usually diminish the sum amplitude since it is normally
always in control of the
limiter gain.
Thus, monaural AM
will
not be
sacrificed.
The
AM stereo
signal may
not achieve the
greatp.st possible loudness, but
the stereo sound will
resemb:e
the original separation.
The studio Dominator
provides simple
front panel selection of the "Tracking" mode.
Some applications other
than AM Stereo
which make use
of
matrixed limiting are
satellite stereo transmissions,
and tape
recording.
The chief advantage of
matrixed recording is that
azimuth
errors 11pon playback show up as
ster~o
high frequency
separ~tion
reductions rather than monaural high frequency loss.
Some radio
stations
reco~d
music tape
ca~tridges
in
the matrixed
format
often with noise reduction to improve
'the
reproduced consistency
and
quality.
Using
the
matrixed
Studio
Dominator
in
the
recording
system
can
allow
higher
average
recorded
levels
withol1t distortion or compressed sound.
This can eliminate
the
need for noise
reduction and the
attendant loss of
d~tail
and
23
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