18-10-2012, 05:22 PM
Surround Sound Past, Present, and Future
[attachment=36622]
A history of multichannel audio from mag stripe to Dolby Digital
Origins of surround sound
The first commercially successful
multichannel sound formats were
developed in the early 1950s for the
cinema. At the time, stereophonic
sound, a concept new to the public,
was heavily promoted along with new
wide-screen formats by a film industry
feeling threatened by the rapid
growth of television. Unlike the twochannel
format later adopted for
home stereo, film stereo sound started
out with, and continues to use, a
minimum of four channels.
With such film formats as fourtrack
CinemaScope (35 mm) and
six-track Todd-AO (70 mm), multiple
sound channels were recorded
on stripes of magnetic material
applied to each release print. To play
these prints, projectors were fitted
with playback heads like those on a
tape recorder, and cinemas were
equipped with additional amplifiers
and speaker systems.
From the outset, film stereo
featured several channels across
the front, plus at least one channel
played over speakers towards the rear
of the cinema. At first the latter was
known as the effects channel, and was
reserved for the occasional dramatic
effect—ethereal voices in religious
epics, for example. Some formats
switched this channel off by means
of trigger tones when it wasn’t
needed because the track on the
film was particularly narrow, and thus
very hissy.
Although film stereo lost favor in
the 1960s and early 1970s due to high
costs of the magnetic formats and a
slump in the film business, sound
mixers continued to experiment with
the effects channel. Formats such as
six-track 70 mm magnetic (see
sidebar) provided consistent signal-tonoise
ratios on all channels, so mixers
could use the effects channel to
envelop the audience in continuous
low-level ambient sounds. The effects
channel came to convey greater sonic
realism overall, not just the occasional
dramatic effect.
This expanded, more naturalistic
application came to be known as
surround sound, and the effects
channel as the surround channel. The
extra speakers at the rear—and now
along the sides of the cinema as well
to create a more diffuse soundfield—
came to be known within the industry
as “the surrounds.”
Home stereo and quadraphonic sound
Bell Laboratories’ famous experiments
with stereo sound in the 1930s
used three channels. Cinema stereo in
the 1950s was using no less than four
channels, and as many as seven. Yet
when stereo finally made it into the
home in 1958, only two channels were
used. This was not because of listener
preference, or some predisposition on
the part of audio professionals. Rather,
two channels (left and right) were all
that the then-prevalent LP phonograph
record could accommodate.
Dolby and film sound
In the mid-1970s, Dolby Laboratories
introduced a new sound
technology for 35 mm prints originally
called Dolby Stereo. Instead of
being based on magnetic striping, it
used the photographic, or optical,
soundtrack technology used to put
mono sound on film since the 1930s.
To enable compatible playback in
mono cinemas, it was necessary to fit
the new stereo soundtrack into the
same space on the print occupied by
the traditional mono track. Experiments
showed that two tracks, treated
with Dolby A-type noise reduction,
could give excellent fidelity. But
trying to squeeze in more than two
tracks raised noise to an unacceptable
level, even with noise reduction.
Two channels, however, were not
enough for movie stereo. Movie
screens are so wide that as well as
the usual left and right channels,
a separate center channel and speaker
are required to localize dialogue for
viewers seated off-center. In addition,
“stereo” and “surround” had become
synonymous to most of the film
industry, so a surround channel was
also a must. Thus a way had to be
found to encode just two physical
tracks on movie prints with four
channels of information: left, center,
right, and surround.
[attachment=36622]
A history of multichannel audio from mag stripe to Dolby Digital
Origins of surround sound
The first commercially successful
multichannel sound formats were
developed in the early 1950s for the
cinema. At the time, stereophonic
sound, a concept new to the public,
was heavily promoted along with new
wide-screen formats by a film industry
feeling threatened by the rapid
growth of television. Unlike the twochannel
format later adopted for
home stereo, film stereo sound started
out with, and continues to use, a
minimum of four channels.
With such film formats as fourtrack
CinemaScope (35 mm) and
six-track Todd-AO (70 mm), multiple
sound channels were recorded
on stripes of magnetic material
applied to each release print. To play
these prints, projectors were fitted
with playback heads like those on a
tape recorder, and cinemas were
equipped with additional amplifiers
and speaker systems.
From the outset, film stereo
featured several channels across
the front, plus at least one channel
played over speakers towards the rear
of the cinema. At first the latter was
known as the effects channel, and was
reserved for the occasional dramatic
effect—ethereal voices in religious
epics, for example. Some formats
switched this channel off by means
of trigger tones when it wasn’t
needed because the track on the
film was particularly narrow, and thus
very hissy.
Although film stereo lost favor in
the 1960s and early 1970s due to high
costs of the magnetic formats and a
slump in the film business, sound
mixers continued to experiment with
the effects channel. Formats such as
six-track 70 mm magnetic (see
sidebar) provided consistent signal-tonoise
ratios on all channels, so mixers
could use the effects channel to
envelop the audience in continuous
low-level ambient sounds. The effects
channel came to convey greater sonic
realism overall, not just the occasional
dramatic effect.
This expanded, more naturalistic
application came to be known as
surround sound, and the effects
channel as the surround channel. The
extra speakers at the rear—and now
along the sides of the cinema as well
to create a more diffuse soundfield—
came to be known within the industry
as “the surrounds.”
Home stereo and quadraphonic sound
Bell Laboratories’ famous experiments
with stereo sound in the 1930s
used three channels. Cinema stereo in
the 1950s was using no less than four
channels, and as many as seven. Yet
when stereo finally made it into the
home in 1958, only two channels were
used. This was not because of listener
preference, or some predisposition on
the part of audio professionals. Rather,
two channels (left and right) were all
that the then-prevalent LP phonograph
record could accommodate.
Dolby and film sound
In the mid-1970s, Dolby Laboratories
introduced a new sound
technology for 35 mm prints originally
called Dolby Stereo. Instead of
being based on magnetic striping, it
used the photographic, or optical,
soundtrack technology used to put
mono sound on film since the 1930s.
To enable compatible playback in
mono cinemas, it was necessary to fit
the new stereo soundtrack into the
same space on the print occupied by
the traditional mono track. Experiments
showed that two tracks, treated
with Dolby A-type noise reduction,
could give excellent fidelity. But
trying to squeeze in more than two
tracks raised noise to an unacceptable
level, even with noise reduction.
Two channels, however, were not
enough for movie stereo. Movie
screens are so wide that as well as
the usual left and right channels,
a separate center channel and speaker
are required to localize dialogue for
viewers seated off-center. In addition,
“stereo” and “surround” had become
synonymous to most of the film
industry, so a surround channel was
also a must. Thus a way had to be
found to encode just two physical
tracks on movie prints with four
channels of information: left, center,
right, and surround.