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You might have noticed that both the Surround Sound Discography home page and the MultiChannelSound Shop cover page distinguish between quadraphonic and Ambisonic recordings. That's because they are distinctly different. All the quadraphonic systems simply provide a mechanism for approximating the four corner signals created by a recording engineer and feeding these to the four speakers of a surround-sound playback system.
In contrast, the purpose of Ambisonics is to create an accurate psychoacoustic illusion of a sonic event. For live recordings, it accomplishes this by capturing the musical performance with a single microphone which records an omnidirectional signal and three directional signals, left/right, front/back and up/down. If you read Ambisonics literature, you'll see these referred to individually as the W, X, Y and Z signals, and collectively as B-format. You can see easily that these are not the left front and back and right front and back signals of quadraphonics.
Currently available Ambisonic recordings, mostly from Nimbus, contain only the W, X and Y signals. Ambisonic decoders use the W, X and Y signals to create four or more speaker feeds for the horizontal sound field. If you have a source with independent W, X and Y signals, you can feed these directly to an Ambisonic decoder. However, until recently, most consumer audio sources supported only two signals. To accommodate this limitation, a UHJ encoder combines the W, X and Y signals into two signals. You can feed these two signals directly to a stereophonic playback system, or send them to an UHJ decoder. The decoder first reconstructs the W, X and Y signals from the two-channel source, and then creates the speaker feeds from the W, X and Y signals.
Though almost all available Ambisonic recordings were made live with a single microphone, Ambisonics supports audio mixing, including movement of sounds around or across the sound field, or even rotation of the sound field. Therefore, it is capable of producing spectacular sonic effects, according to the desires of the performing artist and recording engineer.
From this very brief description, you can easily understand that the decoder you need to playback Ambisonic recordings is entirely different from the decoders for the quadraphonic systems.
If you're interested in learning more about the technical aspects of Ambisonics, visit the The University of York Music Technology Group's home page for Ambisonics and related 3-D audio research. For an assorted feast of information, visit Ambisonic.net. At Ambisonic.net, check especially the article "Whatever Happened to Ambisonics". Also, be sure to check the Ambisonic articles at my own MCS Review On-Line Reprints.
To play Ambisonic sources, I use a Minim AD10 decoder, a unit that I sold during the '80s. This model and, to my knowledge, all Ambisonic decoders of that time period are no longer made. Currently, Meridian and Cantares offer surround processors that include Ambisonic decoding. Meridian offers the 561 Surround Controller ($5,000), 568.2 Surround Controller ($6,500) and 861 Reference Surround Processor ($15,500). Cantares offers one unit, the SSP-1 Surround Sound Processor/Decoder ($1,259). An Audio Media review of the Cantares decoder describes its capability to decode matrix quadraphonic sources as well.
With the demise of Nimbus Records, there are few UHJ-encoded Ambisonic recordings in print today. At least one is available from Cowboy Junkies: "The Trinity Session". The credits state: "A Digital R-Dat Recording, using only a Calrec Ambisonic Microphone." There are also rumors that "Whites Off Earth Now" and "The Caution Horses" are UHJ-encoded. "The Caution Horses" credits say nothing about the recording technology employed. On the other hand, the "Whites Off Earth Now" credits state: "Captured live at Studio 547 on June 28, 1986 on a digital two track using only a Calrec Ambisonic Microphone. According to HighFidelityReview.com, on December 5th, 2006, Mobile Fidelity Sound Lab will release a 20th anniversary 5.1 surround SACD edition of "Whites Off Earth Now", so that more or less confirms that the orignal was UHJ-encoded.
Frank Perry is another artist who has made at least a few Ambisonic recordings. His album "Zodiac" on the Celestial Harmonies label is readily available (at least on eBay). Five others are available on Perry's own label, Mountain Bell Music. The UHJ-encoded Ambisonic titles include "Infinite Peace" (BEL CD 002), "Peace Eternal" (BEL CD 003), "Crystal Peace" (BEL CD 004), "Star Peace" (BEL CD 005) and "Divine Peace" (BEL CD 007). For some, cassette versions are available.
Last updated: November 26, 2006