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For the AES 19th International Conference on Surround Sound in Bavaria in June 2001, the author designed experiments and stereo demonstrations comparing Ambiophonic (front stage only), INA/MMA [7, 8], and OCT Optimized Cardioid Triangle [6, 9, 10, 11] of orchestra, brass quintet, and 180ƒ "Walkabout" localization test made with an Ambiophone prototype made by the author. At the conference held at Schloss Elmau, attendees in the Ambiophonic demonstration room were able to hear recreated the nearly 120ƒ stage width of the brass quintet session, with or without Ambisonically convolved ambience surround [12]. To demonstrate compatibility with 5.1, these recordings were also played for a large audience in the Grosser Saal (Great Hall - theater) using five-channel cinema speaker layout, and in autos with 5.1 and Logic Seven.

For the AES 111th Convention in New York City and this paper, the work was expanded to PanorAmbiophonic 360ƒ reproduction with simultaneously made recordings of opera, guitar quintet with audience, marching bands, and a 360ƒ Walkabout test [13]. Program material was chosen to represent a variety of musical genres in concert hall, studio, and outdoor acoustics. Recordings were demonstrated during Tech Tour 8 at the Ambiophonics Institute on both PanAmbio 4.0 and ITU 5.0 systems, along with a prototype automobile PanAmbio system.

Design and calibration of the microphones and their baffles are more critical for proper surround localization because the results can be discriminated. In the authorís forty years of professional experience with many microphone approaches, OCT and sphere derivatives offer both good localization and spatial impression ñ in the past more typically an either/or choice ñ plus the envelopment of surround sound. For ITU 5.1, OCT uses the directional characteristics of cardioid and supercardioid microphones to image front stage sources with unambiguous phantoms among three loudspeakers (Figures 7a, b).

If more than the 6dB rejection of back sounds is needed, a baffle can add 7dB. Hall sound is added to LS, RS using back-facing cardioids, or to L, R, LS, & RS using a surround reverb convolver or four-channel room microphone such as side-facing figure-8s [6, 14]. 

As the basis for Ambiophonic (front only) recording, where ambience is convolved from hall impulse responses for two-channel recordings, the sphere microphone [15] - a frequency-dependent analog of the human head without pinna ñ is shown idealized for mid-frequencies (Figures 8a, b). When baffled, its stereo characteristics ideally show nearly 10dB of back rejection (Figures 9a, b). The authorís prototype Ambiophone, measured every 15ƒ with filtered pink noise in a non-anechoic studio, approaches these ideal characteristics (Figures 10a, b).

Combining two such spheres for PanAmbio reproduces the full 360ƒ horizontal plane within ±1dB (Figures 11a, b). For the readerís experimental verification, simultaneous recordings using both OCT and the authorís prototype PanAmbiophone are available in evaluation DTS-encoded CDs, described later, along with an early consensus of subjective opinions of each.