Boxoffice-June.1991

SOUND ADVICE
SPECTRAL RECORDING
SOUNDTRACK COMPATIBILITY
By Norm Schneider
President
Smart Theatre Systems
TECHNOLOGY
IS RACING ahead in all
fields of electronics. New products,
processes, and practices appear so frequently
that it is almost a full time job to
keep up with developments. The one area
of motion picture presentation that has
changed most in the past few years is cinema
sound. With five different (or proposed)
digital formats in development, we
may see another change that will affect the
theatre owner and patron in the near future.
Premium home VCR and laser disc equipment
already have a form of digital sound
and the cinema soundtrack appears to be
heading that way also.
At this moment in cinema history we
have something that, //; my opinion, is almost
as good as digital. At the offset of this
article it should be clear that I am a supporter
of the Spectral Recording (SR) process
developed by Dolby Labs a few years
ago for the studio and production industry,
and applied to film soundtracks about two
years ago. This new process pushes the
limits of the optical analog soundtrack well
beyond anything that has yet been accomplished,
but has the handling ease of any
standard optical soundtrack. There is a
strong argument to be made that the sound
quality captured on the SR soundtrack exceeds
the fidelity capability of a majority of
cinema sound systems playing daily around
the world. There is a problem though; only
a small percentage of cinemas are properly
equipped to play the SR soundtrack.
In conversations with theatre owners I
was surprised to find that a large number do
not know what Spectral Recording is and
why it is different from standard stereo
sound. I learned that some sound engineers
have been called to their client's cinemas
for a service call because someone thought
that the sound system sounded strange, only
to discover that the print had an SR
soundtrack. There have been articles and
industry discussions on the compatibility of
SR prints and standard SVA stereo prints.
The differences are still "fuzzy" for many.
1 hope this article will shine a little light on
the subject and how it affects your cinema
presentation.
In the beginning Spectral Recording
soundtracks were issued on a separate invenroiy
print that could be requested by
theatres equipped for the SR process. Everyone
else got the standard optical stereo
print. Having two different prints is expensive
for film producers and causes headaches
in distribution. The practice of
separate inventory was replaced recently
by the sini'le inventory print. That is, if a
soundtrack was recorded in SR. all prints
were encoded with SR sound, and all thea-
The differences in
compatibility between
standard stereo sound and
SR stereo are minor; the
benefits of SR , however,
are major: a new degree of
realism in theatrical sound
presentations.
Ires got SR prints, whether they were properly
equipped to play them or not.
The Spectral Recording process is not a
"hype and jive" promotional gimmick that
Hollywood is sometimes famous for. There
are some real technical differences between
SR and regular stereo in the processing of
the sound during the encoding of the
soundtrack. The decoding process in the
theatre sound system must be complementary
in order to bring the sound back to its
original condition. The encoding/decoding
process overcomes the inherent limitations
of storing sound on an optical media. Decoding
SR material involves special noise
reduction cards in the sound system that can
be switched into the
system when an SR
print is played. Dolby offers several noise
reduction cards and an adapter for Spectral
Recording playback, the most common
card being the Cat. #280. The system is
patented by Dolby Labs, but there are alternatives.
Let's pause for a moment to discuss the
technical differences between the standard
stereo optical soundtrack and an SR
soundtrack. In standard stereo, each channel
of the original sound material in the
studio is broken into four frequency bands
of material that are independently compressed
about lOdB before being placed on
the optical soundtrack. In your theatre,
noise reduction circuits in the stereo processor
expand each of the bands about 10 dB
so the sound is restored to its original condition.
In the process the limited dynamics
of the optical soundtrack are enhanced and
the noise reduced for a much better sounding
stereo presentation. Without the encoding/decoding
scheme applied to the stereo
soundtrack the results would harken back to
the days of pre-stereo, with marginal sound
quality due to the physical limitations of the
optical soundtrack.
The processing of the sound for the Spectral
Recording process is much more severe.
Five fixed frequency bands and five
"floating" bands in the playback chain trap
noise for an extremely quiet playback. The
dynamics are increased and more high frequency
sounds can be put on the film without
fear of recorder overload. The
compression and expansion of SR
soundtracks is about 25 dB. That's a lot of
compression. Without a complementary
expansion process in the theatre, background
sounds appear louder. Street noises,
wind, and special effects may equal the
dialogue level, producing an unnatural balance.
The five frequency bands on the SR
soundtrack are in different places than the
four bands of the standard stereo print. An
SR print may appear to sound brighter due
to its ability to handle more high frequency
material.
With the relativelv small number of the-
26 BOXOFFICE