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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 2
Robert E. (Robin) Miller III, FilmakerStudios, Bethlehem, Pennsylvania 18018, USA

4. PRACTICAL 3D - FILLING A NEED?

This paper presents a practical path to more life-like sound that: a) provides uncompromised 2D in 5.1 or stereo today, and b) embeds 3D information for future replay while minimizing obsoleting libraries or consumers collections and preserving priceless musical performances for ever newer audiences. The "tri-play" format deliverable in today's media, combined with high performance in 5.1, stereo, and 3D might increase consumer demand for surround equipment and software today and in the future.

But firstly, why will we want 3D? Because in life, we hear what we see - but also what we don't see. We usually see direct sources, often arranged in a horizontal circle around us. But in non-anechoic conditions, there is much we hear that we can't see - reflections and reverberation coming from all directions of a sphere (Fig. 1). In an acoustic space, each arrival is direction stamped, tonally colored by our unique HRTF, including height colored by comb filtering by our pinna, and is associated with a direction learned from childhood, leading to our unique perception of "live" hearing.


Fig. 1. In life, we hear both sources we see and reflections we don't see; a major factor of tonality, as musicians 'play' the acoustics as extensions of their instruments. Preserving 3D directionality is key to lifelike hearing.

Each musical note triggers a dynamic buildup of differently colored sonic arrivals until all are integrated in the steady state of the note's final timbre. Then after the direct source stops, the multi-colored set of unseen sounds collapses, generally in the order it was built. Musicians 'play' this acoustic response as extensions of their instruments, carefully forming each note while listening as the audience does to this complex seen/unseen interplay of sounds. Preserving the 3D directionality of the native acoustics is key to life-like hearing. Take away true 3D and it sounds "canned".

5.1 is surround sound only in 2D; a circle without height components for our pinna to color. For movies, for which 5.1 was intended, the picture compensates for falling short of fully life-like sound. However, a 3D sonic image would complete the cinema/ATV picture beyond four sides of the frame, not just two. For audio-only such as music, there is no picture, and the illusion more obviously falls short of life-like. To achieve a compelling illusion of 'live', we must preserve the 3D directionality of reproduced sonic components-unseen as well as seen, direct as well as diffuse.

We need a systems approach to 3D full sphere surround sound reproduction, from musicians' instruments to home theater owners' ears, using practical arrays of microphones, channels, and speakers. An objective of the system is to produce 5.1 with quality potentially superior to re-panned multi-track masters originally made for stereo prior to surround. For capturing 3D live, the paper explores a hybrid solution to the deficiencies of any one of the current 3D approaches. However, 3D for renowned acoustic spaces can be convolved from impulse responses, requiring only 2-channel delivery if implemented in user equipment. The system embraces a tri-play release method to transform the 3D information for uncompromised 2D reproduction in 5.1 without decoder or relocating speakers, and folding the captured 3D information by projecting height components onto the horizontal plane of 2D 5.1. This is accomplished by selecting one of a number of defined modes appropriate to the music and venue, but reversible and changeable in the mastering stage. By adding a decoder and speakers, full 3D can be losslessly reconstituted. 6 full-range channels are required, available today in DVD-A, SACD, and DTSES Discrete CD or DVD-V. A 10-speaker isotropic array is described that provides 3D with a broad listening area and also complies with legacy 5.1 releases. However, pseudo-random speaker layouts are explored that users might accommodate more readily.

For audio-only such as music, the tri-play PerAmbio (periphonic-ambiophonic) system described increases entertainment vendors' ROI by reducing costs for 3D re-release and adds value to their libraries and users' collections. In addition, priceless musical performances could be preserved for new audiences that might increase demand for 3D reproduction.

Experimental recordings have been made and informal listening tests and demonstrations conducted in 2003 in conjunction with AES in Amsterdam and Banff. A patent is pending on the processes described.

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