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Audio Engineering Society
Convention Paper

Contrasting ITU 5.1 and Panor-ambiophonic 4.1 Surround Sound Recording Using OCT and Sphere Microphones
Robert E. (Robin) Miller III ©20021

1 FilmakerStudios, Bethlehem, Pennsylvania 18018, USA

Presented at the 112th Convention
2002 May 10-13 Munich, Germany

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.  For a PDF version of this paper (0.5 MG), click here.

ABSTRACT

Two multi-channel microphone techniques for natural music and sound effects reproduction are experimentally compared. Simultaneous surround sound recordings of several genres of music and ambience are made in concert hall, studio, and outdoors. Trained listeners subjectively evaluate the abilities and tradeoffs of each system to recreate accurate panoramic localization and spatial impression of opera, bluegrass with audience participating, flute quartet, brass quintet, marching bands with surrounding crowd and building echoes, and 360° "Walkabout" azimuth test. Differing speaker layouts for 5.1 and "Panor-ambiophonic" Surround are shown to satisfy two distinct listening audiences, which are further divided into home, automotive, and PC markets. An approach to recording level-setting, compatible production, and delivery formats are introduced to satisfy these diverse end uses.

STEREO IN TRANSITION

While it has brought enjoyment to many over the last half century, traditional stereo, with two speakers and a listener at points of an equilateral triangle, falls short of recreating what would have been heard during recording. Implicit problems were known in the 1930s to inventor Alan Blumlein at EMI. Perhaps because it failed to meet expectations of "images in space" analogous to stereoptic "3D" vision, stereoís market acceptance in the 1950s was driven more by ping-pong novelty and phasiness. Content so produced suffered little from manufacturers placing speakers on the sides of a short box, or from consumers placing one speaker in the living room and the other in the dining room! Surround sound offers "realism" that is more compelling of us to record and play it correctly. Why?

Two-speaker stereo suffers from imprecise localization caused by each ear hearing sound not only from its intended speaker, but also "crosstalk" sound from the speaker intended for the other ear (Figure 1). Think of watching a 3D movie without glasses - each eye sees both its image and the one intended for the other eye, destroying the illusion. Phantom images of important central soloists toggle to the nearer speaker for listeners who are off the equidistant (central) plane, and are colored by comb filtering and pinna confusion as to their frontal direction because in fact the speakers are toward the sides. Also, room ambience and other sounds that should be around and behind come instead from the frontal image plane between and beyond the two speakers, confining all reproduced sound to a 60° sector -- only 1/6 of the total panorama.

To compensate for stereoís inadequate spatial impression, recordists space their microphones. Then to improve localization, they make them coincident, or amplitude-pan one microphone per instrument. So stereo "devolved" out of necessity by sound engineers monitoring over two speakers and making compromises between seemingly mutually exclusive localization and spaciousness. Engineers as well as marketers who address this "legacy" in the current evolution from two channels to five or more will more likely achieve surroundís potential.


Fig. 1. Two-speaker stereo creates phantom images between the two transducers that suffer coloration of central voices and pinna confusion as to direction. All sound, including ambience, comes from the front 60°. While superior in spaciousness to monaural reproduction, stereo often falls far short of sounding "natural." [back]

With home cinema an establishing market, ITU 775 has provided a multi-channel surround standard [1] for "5.1" speaker positions and therefore home sound receivers intended for universal replay, including music-only (Figure 2). 5.1 is positioned to replace 2.0 stereo in the home, as it has matrix surround in the cinema. Record-breaking sales of DVD players and movies with multichannel soundtracks on DVD bode well for 5.1ís popular acceptance. Broadening the reproduction soundscape to the entire 360° horizontal plane, 5.1 offers a compatible means of surround cinema and music reproduction and greatly improves spatial impression and adds envelopment, owing to two surround speakers. The author installed a "home theater" in 1999, giving his family and friends much pleasure watching movies on DVD. However for music, available in 5.1 on DTS-encoded audio CDs but mostly not recorded especially for surround (i.e. usually remixed multi-miked masters), there is potential for greater satisfaction. Investigating how much potential, how to achieve it, is it worth it, and what are the alternatives begins with a survey of 5.1ís strengths and weaknesses.


Fig. 2. ITU 5.1 (3/2) standard speaker placement creates five sets of phantom images, one between each pair of transducers, that surround the listener and makes it superior to stereo in "realism." [back]

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