Crestron
Surround Sound
Primer
envelopment. The acoustic design listening spaces usually involves
creating a balance between clarity, definition, and spaciousness.
Listeners often have different preferences regarding this balance.
Temporal Masking
Temporal masking is a defense mechanism of the ear that is activated
to protect its delicate structures from loud sounds. When exposed to a
loud sound, the human ear reacts by contracting slightly, temporarily
reducing the perceived volume of sounds that follow. Loud sounds in
an audio signal tend to overpower other sounds that occur just
before
and just
after
it.
A History of Surround Sound
The simplest method of sound recording is called monaural or mono.
All the sound is recorded on one audio track and played back on one
speaker.
Two-channel recordings played back on speakers on either side of the
listener are referred to as stereophonic or stereo. The simplest two-
channel recordings, (binaural recordings) are produced with two
microphones. Playback of these two channels on two speakers recreates
some of the experience of being present at a concert event. But the
listener must be anchored in the "sweet spot" between the speakers to
maintain the illusion of the phantom sound from between the speakers.
Surround recordings add additional audio channels so that sound comes
from multiple directions. In effect, widening the sweet spot and
enhancing the realistic sound quality.
The term "surround sound" refers to specific multi-channel systems
designed by Dolby Laboratories, but is commonly used as a generic
term for theater and home theater multi-channel sound systems.
Early Surround
Walt Disney's "Fantasia" (1941), was one of the first surround sound
motion pictures. Four separate recordings of each orchestra section
were recorded on a separate reel of film and played through speakers
positioned around the theater.
By the late 1950s, movies were encoded with simpler multi-channel
formats. Several different systems emerged, including Cinerama and
Cinemascope. These systems were referred to as stereophonic sound, or
theater stereo. Stereophonic sound used multiple magnetic audio tracks
at the edges of the film. The standard film format could support two
optical audio tracks or up to six magnetic audio tracks. A four-channel
theater system included: left, right, center speakers behind the screen,
and surround speakers along the sides and back of the theater.
Quadraphonic
In the quadraphonic systems of the early 1970s, two rear surround
channels were combined (matrixed or encoded) with the two front
Primer – DOC. 6122
Surround Sound
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