New readers start here: Researchers in different parts of the world, in particular Duane Cooper in the US, independently discovered some of the "root technologies" for Ambisonics, and thus share the credit with the small group of British academics, notably the late Michael Gerzon of the Mathematical Institute in Oxford, and Professor P B Fellgett of the University of Reading, who brought Ambisonics into being as an integrated high-resolution surround-sound system in the early Seventies.
From the beginning, they conceived Ambisonics as a surround sound system that would overcome the major problems of the so-called "quadraphonic" systems that preceded it.
Traditional "quad" systems relied on two fundamental fallacies:
Modern surround-sound systems get around the second problem by using four or more "discrete" transmission channels, but the first problem remains unsolved. Due to the "hole in the middle" between speakers affecting dialogue audibility in movie applications, Dolby Surround, based on the early quad systems, added a centre-front dialogue channel. This configuration continues in current "5.1" surround systems, the ".1" representing a low-frequency effects channel. These systems do not offer a solution to the problems resulting from fallacy 1 above.
Ambisonics provides significant advantages in that the effect does not sound significantly listener- or speaker-dependent (you can even walk outside the speakers and appreciate the image). In addition, listeners can position the loudspeakers (within fairly wide limits) in any convenient position in the room. Gerzon and associates developed a series of sum and difference signals, called B-Format, which was in some senses an extension of Blumlein's stereo work into three dimensions; and a hierarchy of up to four signals, called UHJ, allowing different levels of mono- and stereo-compatible surround to be carried depending on the available channels. UHJ offers exceptional mono compatibility (exceeding that of conventional "panpotted mono" mixes); impressive "super stereo" without a decoder; stunning horizontal ("planar") surround from a two-channel original with a decoder; exceptionally high-resolution planar surround with three channels (one of which can be bandwidth-limited if desired); and full, with-height surround ("periphony") when four channels are available.
The disadvantage with the UHJ or B-Format approach is that the listener requires a decoder to fully appreciate the surround effect. As a result, modern Ambisonics also focuses on "G-Format" in which the Ambisonic signal (from an Ambisonic multitrack mix, Soundfield microphone or other source) is "pre-decoded" for a standard 5.1 speaker layout, these speaker feeds being transmitted as if they represented a standard 5.1 signal. This method gives the benefit of not requiring a decoder, at the expense of losing some other Ambisonic benefits, such as multiple speaker positions or numbers of speakers. In addition it is not possible to transfer height information via this means without encoding it in a special way (and thus still requiring a decoder at the listening end).
Ambisonics thus offers a number of major advantages over current 5.1 systems: