Audio Engineering Society
Convention Paper

Scalable Tri-play Recording for Stereo, ITU 5.1/6.1 2D, and Periphonic 3D (with Height) Compatible Surround Sound Reproduction - Page 3
Robert E. (Robin) Miller III, FilmakerStudios, Bethlehem, Pennsylvania 18018, USA

5. HYBRID APPROACH TO 3D (PerAmbio)

5.1 (ITU R-775) has renewed interest in localization, now with 5, 6, or 7 speakers, still only in the horizontal plane as in experiments using directional microphones, as OCT by Theile [9] and MMA by Williams [10]. But some tonmeisters at the Banff, Canada, AES 24th International Conference on Surround Sound preferred the timbral result of five spaced omnis, even though instruments jumped around the stage note by note.

However, we hear in many more directions than 5 or 6 and only some of these lie in the 2D horizontal plane (Fig. 1). As our pinna colors differently sound from each direction, the resulting brain-integrated sense of sonic space will not be correct unless directionality in 3D is preserved. Reproduced in 3D, musicians participating in the author's experiments exclaim "Finally, it's my sound. The sound that, together, they, their instruments, and the room synthesized in performance.

At AES114 in Amsterdam and AES24 in Banff, the author demonstrated the theory that if no one surround recording system is perfect [ 2], perhaps a hybrid of two is better. PerAmbio 3D combines a wide, accurate front stage using Ambiophonics [11, 12, 13, 14, 15, 16] with ambience using Ambisonics [ 17]. As in the Appendices and references, Ambio uses a crosstalk-cancelled pair (Ambiodipole) of high quality speakers placed in front 16-24 degrees apart, while Ambisonics uses eight or more satellite-quality speakers placed almost anywhere else (Fig. 2).

Fig. 2. PerAmbio 3D combines an accurate, spacious front stage with tonally correct envelopment using 8 or more satellite-quality speakers positioned flexibly (cube layout shown) as programmed in the decoder. In effect, all speakers disappear, along with the walls of the listening room.

The two components of the PerAmbio 3D hybrid complement each other: Ambiophonics' focused front stage fills in Ambisonics' weak one, while Ambisonic envelopment preserves ambient directionality and frequency response in a listening area that exceeds 5.1/6.1 because more surround speakers playing at lower levels can be approached more closely before they can be localized. Serious listeners on the median plane are believably transported to the recording venue, as all speakers and listening room walls disappear.

Most importantly PerAmbio 2D/3D can then be transformed for media release, and then is uncompromised, in stereo or 5.1/6.1 surround (2D) playback, without any decoder or additional speakers. Then at any time, the home theater owner can add a decoder and additional speakers for the lossless Ambiophonic 3D reproduction, described in detail below.

5.1. 3D for Large Audiences & Cinema

Since PerAmbio 3D/2D is compatible with stereo and 5.1/6.1, a 3D hybrid playback is possible for large audiences such as the cinema by adding flexibly placed height speakers to the standard 5.1/6.1 theater speaker layout. This only compromises frontal sounds for those six theater-goers seated in the theater's 'sweet area' (approx. 1.5m2 [9]) compared to the wide, accuracy of pure ambiophonics that is obtainable when up to four serious listeners play the same PerAmbio 3D/2D transformed mix at home. PerAmbio 3D can also greatly enhance music and sound effects, while dialogue would still mostly be anchored by the center speaker.
Cinema screen speakers are the same for PerAmbio 3D as current standards. Surround and height speakers may be pseudo-randomly positioned and the decoder programmed where they are in azimuth & elevation (same as in home). Height speakers for the theater need not be large, as pure height cues are >1kHz [18].

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