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AFT660 Afterburner & AFT660PnP Digital Plug 'N Play
Introduction
Many theatres added digital sound in order to present
the best available format, but found that their present
power amplifiers and speakers were not up to the job of
handling the increased sound levels without distortion
during the most dynamic portions of the movie. In-
creased dynamic capability means the sound difference
between average dialog levels and the maximum action
sequence can be extremely wide. You cannot simply
add a digital player to an existing sound system with-
out closely studying the capability of the amplifiers and
speakers to reproduce the increased sound levels. Most
existing cinema stereo systems were designed to ad-
equately handle the maximum levels of optical stereo.
With louder sounds created by more channels and
more dynamic range, more sound pressure is produced.
This can cause annoying “sound bleed through” to ad-
jacent auditoriums through common air conditioning
ducts, passageways, a common ceiling and thin walls.
A common complaint from audiences about digital
sound systems is that the sound is too loud. Our hear-
ing is most sensitive to mid-range frequencies. Louder
mid-range sounds appear to be sharp or piercing in
proportion to the bass frequencies. A skilled recording
artist can fix this in the mix by re-equalizing the track
during loud sequences to minimize the subjective harsh
sound. Unfortunately, you cannot control the content
of the soundtrack you receive. An operator who is re-
sponsible for 12 booths cannot run to a single booth
and turn it down every few minutes. Often, what hap-
pens is the sound level is set to compensate for the
loudest parts of the movie and the dialog is then hard to
hear.
The Model AFT660 AFTERBURNER from SMART
solves all of these problems. The AFT660 is an auto-
matic 6-channel threshold limiter that “burns off” the
top dynamic range of the soundtrack. Unlike simple
compressors or peak limiters, this circuit does not affect
the sound dynamics until the threshold (which is ad-
justable) has been reached. All louder sounds are then
reduced by a 2:1 ratio above the threshold. The AFT660
is extra sensitive to the mid-range frequencies that our
ears are most sensitive to. The stage and surround
channels track together to keep the channels balanced
whenever one of the channels reaches its threshold.
The subwoofer’s threshold level is set separately from
the other channels.
The chart below shows how the sound pressure is con-
trolled when the threshold is reached. The actual
threshold point is set by the installer in the auditorium.
Some theatres would require a lower threshold level
than others. The end result is that a normal dialog level
can be achieved consistently and the loud passages are
controlled automatically. The AFT660 is installed be-
tween the output of any digital player and the rest of
the system. Convenient plug in cables make the instal-
lation quick and easy. The product only occupies 1 3/
4” of rack space. An emergency bypass switch on the
front of the product will hard wire the digital player
around the AFT660 so that it won’t cause a failure to
the digital system.
If the system amplifiers and auditorium speakers are
not quite big enough, the AFT660 will control the
amount of power that is fed to them. A reduced sound
level means less complaints from patrons and less
sound bleed through to other auditoriums. The action
of the limiters has been carefully shaped so that you
cannot hear the product working. The resulting sound
would appear to be similar to a good optical SR print.
However, all the other sterling attributes of the digital
recording are preserved, such as extended fidelity, no
soundtrack noise and low distortion.
Installation and Operation Manual
AFT660 Afterburner
For Digital Systems
