Branch Meeting - February 21, 2002
History and Future of Surround Sound
Author: Mr. Don Winter
Speaker: Dr. Tomlinson Holman
Dr. Tomlinson Holman (the TH in THX) presented a talk on the History and Future of Surround Sound to the Southern California Branch of the IEE, on February 21st, 2002.
Experiments with stereo sound began at Bell Labs in the early 1930s, including one experiment in which Leopold Stokowski and the Philadelphia Orchestra were captured by microphones in the Academy of Music in Philadelphia and relayed over 15 KHz phone lines to the labs in New Jersey. (The recordings made of those sessions exist to this day). Later Stokowski participated in the sound track recording for Disney's "Fantasia", which used tracks for more than just the frontal sound and was thus the first 'surround sound' recording.
These experiments established that the optimum number of channels for "stereo" was greater than two, and that a center channel was highly desirable, and the early commercial studio recording onto magnetic tape in the early 1950s used at least three channels. However the commercial introduction of stereo in 1957 was limited to two tracks because that was all that could reasonably be accommodated by the Long Playing Record of the time. In the early 1970s, there were several attempts to 'matrix' two additional channels onto the LP, but none were commercially successful (and some would say none were technically successful, either).
Motion picture releases provided more promise in terms of being able to carry additional soundtrack channels. However, the attempts in conjunction with Cinerama and the like in the 1950s were unsuccessful mainly because what was achieved in purpose-built cinemas in Los Angeles and New York City could not be replicated economically for the vast majority of moviegoers.
By the mid 1970s, movie studios were ready to try again. "Star Wars" pointed the way (although it was not the first release with "surround" sound). Dolby Labs invented the matrixing technique commercialized as Dolby Surround. The number of channels was still limited, however, and since the surround channels were mono, the result was not very realistic. "Apocalypse Now" nonetheless made great strides in the use of surround audio to draw the audience into the action.
Digital Audio changed all of this, and made multi-channel setups possible and realistic, in the cinemas initially, and later in Home Theater. The current standard has "5.1" channels, with the ".1" being a special bass effects channel directed to a subwoofer. Many current Home Theater systems provide bass management facilities that use the subwoofer for all of the sounds in the bass frequencies, not just those recorded in the effects channel. This represents the first relaxation of the idea that "pipes" should correspond to "loudspeakers".
Having described the history, Tom then spent the rest of his talk discussing the potential future(s) of surround audio.
There are three major variables in digital audio encoding: frequency range (or sampling rate), dynamic range (or bits per sample), and number of channels. All of these are subject to "saturation" (a value above which no improvement can be heard by the listener). Saturation of frequency range occurs by a sampling rate of 60 Kbits/sec.; saturation of dynamic range occurs between 20 and 24 bits/sample. Experiments have not yet shown a saturation point for number of channels. This latter factor is thus where the greatest future improvement may lay.
So far, each major step along the way has resulted in an approximate doubling (or trebling) of the number of channels. This suggests looking at 10.2 channels (ten full range and two bass only) as the next step forward. Tom suggests that five speakers across the front, two on the sides, and three across the rear would be a reasonable configuration for such a system. The next step after "10.2" is to include the vertical (height) dimension.
Human auditory spatial acuity is good to the front, in both horizontal and vertical dimensions, not as good to the rear, much less good to the sides and above. Humans can hear stereo imaging between pairs of loudspeakers to the front and (less well) to the rear, but not to the sides. Tom described experimental results from a variety of researchers, with 30 channels in a horizontal circle around the listener up to hundreds or thousands of channels arranged on the inner surface of a sphere to recreate an entire acoustic wavefront around the listener.
Tom talked about some experiments that his current company has performed to see how many loudspeakers provided the "optimum", and how they should be distributed spatially. These experiments have also separated the "pipes" from the "speakers", with processing capability determining how to transform (say) 14 pipes into 10.2 speaker channels in the optimum fashion for both the material and the environment. No definitive conclusions on number of channels, spatial distribution, or processing of pipes into channels have been reached and research is continuing.
In discussion after the meeting one participant suggested that the processing from storage to reproduction environment might include at least some compensation for the acoustic characteristics of the listening environment.
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Document last updated - February 14, 2004