|The Science of Domestic Concert Hall Design|
by Ralph Glasgal
Ambiophonic + Ambisonic 3D Surround Sound to & from ITU 5.1/6.1
1 FilmakerStudios, Bethlehem, Pennsylvania 18018, USA
Presented at the 114th Convention 2003 March 22-25 Amsterdam, The Netherlands
This convention paper has been reproduced from the author's advance manuscript, without editing, corrections, or consideration by the Review Board. The AES takes no responsibility for the contents. Additional papers may be obtained by sending request and remittance to Audio Engineering Society, 60 East 42nd Street, New York, New York 10165-2520, USA; also see www.aes.org. All rights reserved. Reproduction of this paper, or any portion thereof, is not permitted without direct permission from the Journal of the Audio Engineering Society.
ITU 6.1 with six discrete full-range audio channels, implemented in DVD-A, SACD, and DTS-ES Discrete, provide the means to deliver full sphere periphonic 3D surround sound. For compatible distribution, the channels are transformed for 5.1/6.1 reproduction, but can still be fully recovered for "PerAmbio" reproduction - an Ambisonic + Ambiophonic hybrid approach, described in a prior paper, that maximizes 3D envelopment along with front stage imaging and spaciousness, while economizing the number of channels and speakers. To clarify that fewer media channels "r" are required than speakers "s" the use of MCN - multichannel numbering, in the form "r.lfe.s" is proposed. Experimental "PerAmbio 6.1.10" (10 speakers or more + subwoofer) recordings test six encoding variations applicable in home theater, virtual reality, and music-only production.
PURPOSE OF PAPER
The surround audio market is driven by upgrading by growing numbers of DVD owners from 2-speaker stereo to multichannel surround in the horizontal plane. However judging by the response to the author's "periphonic" demonstrations to date, full sphere 3D surround is compelling and desirable. To listeners it is just as astonishing when height is present, as, conversely, it would be astonishing in real life were 3D absent. Audio engineers need to consider the consequences of not including a path to 3D in production, transmission, and reproduction standards.
This paper reports a method for transforming ěPerAmbioî full sphere 3D to dual-format recordings that play directly in standard ITU 5.1/6.1 horizontal 2D surround with no extra decoding or relocation of speakers. Only when users choose to recover "full sphere 3D" surround would they need the described converter that derives 10 or more speaker feeds, plus subwoofer(s). This production, transmission, and reproduction system is applicable in music, cinema, broadcast, amusement ride, and Webcast markets.
Compatible with 5.1 AND extensible to 3D
Even as we progress toward the ultimate sonic experience - fully periphonic 3D sound of natural hearing - it is imperative that systems be compatible with 2D standard ITU 5.1 surround . This premise not only recognizes the popular acceptance of 5.1, it also considers the value to entertainment providers and their customers of software libraries that need not be rendered obsolete - if both parties plan for the future. The new 3D systems described here and in prior papers are not intended to compete with 5.1 - they are the next step in the evolution started by it [2,3].
Compatibility with ITU 5.1/6.1 implies that:
… New 3D recordings should be able to play without compromise on current, standard 2D ITU 5.1/6.1 surround systems, such as in home theaters;
… Existing 5.1 and legacy 2-0 stereo recordings should play (possibly better) on 3D layouts;
… Users, manufacturers, and record companies should benefit by having choices - and by being able to make them in steps as it suits them.
For example, if manufacturers pre-elect to offer hardware and entertainment providers software along lines outlined in this paper, then the following scenario could play out in the marketplace:
1. Initial user step - Foresighted consumers comprise a demand for recordings made in 3D PerAmbio 6.1 (possible today using DVD-A, SACD, and DTS-CD) and initially enjoy them on their standard 2D ITU 5.1/6.1 systems;
2. Optional interim user step: Serious listeners can enjoy 2D PanAmbio 4.1 recordings (compatible with 5.1/6.1) using two closely spaced speaker pairs and crosstalk cancellation . At least one manufacturer will offer this capability in 2003.
3. Ultimate user step - The user upgrades to fully periphonic 3D using the converter described in this paper, which reconstitutes from the 6 distribution channels 10 or more unique speaker feeds. Legacy 5.1/6.1 and stereo recordings can also be enjoyed as illustrated in Fig.1.
PerAmbio 6.1.10+ is extensible to 3D and scalable from 10 speakers, to 14, to a practical maximum of 26, plus subwoofer(s). Dual-format PerAmbio recordings can be released that play in 5.1/6.1 and with a decoder in 3D, making future-proof priceless recorded performances and saving having to re-record others for 3D. Capable media such as DVD-A, SACD, and DTS-CD already exist for the music industry. However, existing broadcast standards need to be implemented for more than the 5 channels of AC-3, such as 48-channel AAC of the Advanced Television Standard. A more detailed description of PerAmbio 6.1.10+ appears later in this paper, and its requirements are summarized in Appendix A.
Fig.1 PerAmbio 6.1.10+ in plan view illustrates the minimum of ten speakers (plus subwoofer) - white at ear level, black on floor, gray at ceiling. By relocating the listener back 26% of the speaker layout diameter, speakers comply with ITU 5.1 angles.