1600 Chapter 45
What has been needed is a way to establish a play-
back reference level based on the actual measured
acoustic output of the listener’s playback system. The
scientifically correct compensation could then be
applied based on the listener’s preferred listening level
relative to the reference level. The lower the level, the
more compensation would be applied.
Measuring the acoustic output of a home system was
once beyond the realm of practicality. Today, however,
it happens all the time in home theater systems featuring
audio-video receivers (AVR) equipped with automatic
loudspeaker balancing. The majority of mid- to
high-end AVRs has built-in noise generators and
provides a microphone making it possible to measure
the loudness of each loudspeaker from the listening
position and automatically adjust it to match the others.
Taking advantage of this built-in feature, several tech-
nologies, including Dolby Volume, THX Spectral
Balancing, and Audyssey Dynamic EQ, have been
recently introduced that make it possible to establish a
reference playback level in the home, and apply appro-
priate loudness compensation at lower levels. It is now
possible to automatically achieve at any level the same
balance of low, middle, and high frequencies, and of
main to surround channels, as at reference level,
bringing home reproduction that much closer to what
sound mixers achieve in the dubbing theater or music
studio.
45.9 What’s Next for Surround Sound?
5.1 remains the standard for film-based cinema, with
EX used with some regularity for big epic and sci-fi
films. This is in part because of cost and complexity
issues, in part because the movie industry is pouring its
resources into converting to digital cinema, and in part
because of the industry’s overall industry satisfaction
with 5.1 both artistically and with respect to cost-effec-
tiveness. After all, as stereo pioneer Harvey Fletcher put
it way back in the 1940s,
Stereophonic systems do not consist of two,
three, or any other fixed number of channels.
There [only] must be sufficient of these to give a
good illusion of an infinite number.On the other hand, digital cinema content is capable
of delivering twenty or more channels of uncompressed
PCM audio. Even with the increasing number of digital
cinema installations, however, 5.1 remains the standard
for digital releases. Not only is equipping cinemas with
more playback channels expensive, but so is mixing
soundtracks with more channels, particularly since
mixing is one of the final postproduction steps when
time may be running out. Moreover, whether to use the
additional channels—and if so, which ones—is wide
open. As the SMPTE puts it in its standard for digital
cinema channel mapping (428-3-2006), “This standard
is not intended to define the suitability of these channels
to a particular track, nor to specify that all the channels
described herein will be used,” Table 45-1.
Because the movie industry has not yet ventured into
the realm of more than 5.1 discrete channels, it
continues to deliver 5.1 content for broadcast and video
disc release. But that isn’t stopping the consumer
electronics industry from experimenting with 7.1
discrete audio content, just pioneered matrix 7.1 play-
back. Both Blu-ray Disc and HD DVD have ample
storage capability for more channels, whether uncom-
pressed PCM, or using lossless or lossy coding technol-
ogies offered by both Dolby and DTS. A few hardy
pioneers are going back to movie soundtrack stems and
remixing titles in discrete 7.1 for high-definition disc
release, with the blessing and supervision of the film’s
producers.
Playback in 7.1 discrete depends on home theater
AVRs equipped with appropriate decoders, and both
players and AVRs equipped with HDMI 1.3 connec-
tivity, which is far from universal. It’s impossible to
predict just what will happen, but it’s conceivable that
the consumer electronics industry, whose surround
sound technology so far has mostly migrated from the
movie industry, may wind up ahead in the multichannel
race—assuming consumers buy into it, of course.
Perhaps more significant than the potential for more
channels, however, are the rapidly expanding opportuni-
ties for delivering 5.1 content. New broadcast standards
developed to take advantage of new, more efficient
video and audio codecs alike all feature 5.1 capability.
These new codecs are fostering new delivery methods,
such as IPTV, for 5.1 audio. And the future is likely to
offer 5.1 download opportunities, such as Apple’s
pioneering effort enabling the purchase and rentals of
downloaded high-definition movies with Dolby Digital
5.1 audio. Indeed, there are those predicting that in the
foreseeable future the Internet will overtake discs as the
prime conduit for movies and other surround content
into the home.
Regardless of what the future brings, however,
surround sound has come a very long way already, from
rarefied and costly magnetic sound in cinemas 50 years
ago, to home theater audio systems costing as little as a
few hundred dollars today. Involving the viewer is what
surround is all about, and there’s no doubt that movie-
goers and home viewers alike prefer—even