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The Ambiophone
Derivation of a Recording Methodology Optimized For Ambiophonic Reproduction

By Ralph Glasgal

Presented at the AES 19th International Conference on Surround Sound Techniques, Technology, and Perception
June 21-24, 2001, Schloss Elmau, Germany

For a copy of this article in its entirety, click here
(PDF, must have Acrobat Reader)

Ambiophonic surround systems reproduce both existing and new 2-channel music discs with unprecedented spatial realism. This paper extends this binaural technology concept to recording. It describes microphone, live recording and studio monitoring techniques that take advantage of the foreknowledge that playback will be Ambiophonic to produce music recordings of exceptional "you-are-there" concert-hall realism, fortuitously and optimally, still needing just two media channels.

Introduction

There exists an affluent, elite group of classical music lovers, high-fidelity enthusiasts, audiophiles, and musicians who value realism in music reproduction above all other considerations. Ambiophonics, a public domain technology supported by the non-commercial Ambiophonics Institute, is a no holds barred methodology designed to appeal to such devoted listeners and displace stereophonics as their preferred route to audio nirvana. Thus Ambiophonics is deliberately configured to enhance acoustic and virtual music recording and reproduction and makes no compromises in fidelity to accommodate movie sound tracks, off-stage direct sound sources or listening by large groups.

The goal of Ambiophonics is to deliver to one or two home listeners a realistic replica of the concert hall experience. In this context, realism does not necessarily need to equate to accuracy. A recording made in Carnegie Hall but played back in Avery Fisher Hall can seem very real but is not accurate. Ambiophonics aims to provide a concert-hall, opera house, church, cathedral, theater, rock pavilion, etc. musical experience, at home that the brain will accept as real. Real, not accurate and not necessarily perfect just as real concert halls are not ideal.

The Ambiophonic method [1] combines an exploitation of under-appreciated psychoacoustic principles [2, 3, 4] with the basic rules of good musical performance-space design [5, 6, 7] to create believable concert-hall soundfields in a home listening room. Ambiophonics moves the listener into the same space as the performers by accommodating to individual pinna characteristics, [8, 9] minimizing interaural correlation at the listening positions, abandoning the traditional stereo loudspeaker triangle (including the center speaker in 5.1), generating early reflections and reverberant fields from a library of stored real-hall impulse responses, and using room correction/treatment technology to insure that listening room early and late reflections are essentially inaudible. Fig. 1

Ambiophonic reproduction of music combines crosstalk cancellation, [10] novel speaker placement and shape, and real hall ambience convolvers (Ambiovolvers) feeding surround loudspeakers to achieve the holy grail of binaural technology i.e. delivering to each ear an almost exact replica of what that ear would have heard if it had been at the microphone position during the live performance. Fig. 2

The reason that there are already so many references cited in just the first few paragraphs of this paper is that I would be the first to concede that there is nothing about Ambiophonic technology that I did not find in the existing literature after I thought to search for it. That there is nothing new under the sun is not as extraordinary as that all this preexisting research has been so resolutely ignored.

Ambiophonics has been shown [1, 11] to be remarkably compatible with and able to reproduce existing two channel classical music LPs, CDs and DVDs with realism, despite the variety of microphone, equalization, mixing, and panning techniques employed. If we define stereo as Blumlein did just meaning reproduction via the equilateral speaker triangle, rather than including all two channel recording methods, it is clear that most two-channel recordings are not usually, if ever, inherently stereo. That is, there is nothing basic in the recording process, using microphones or virtual sound processors, that relies on the facts that the localization will be by phantom imaging, that stage width will be restricted to the angle between the speakers, that there will be pinna angle errors and head shadowing errors for central sources, unpredictable comb filtering, rear and side ambience coming, instead, from the front, and so on.

While recording engineers in control rooms may monitor their creations using the stereo triangle there is little they can do to compensate for these problems in their mixes. Almost all panning programs for virtual reality recordings are likewise deficient in most of these areas. Thus one can say that many so-called stereo recordings can be made to sound more realistic using a binaural technology to play them back than they normally would. Most existing recordings are not inherently stereophonic, (in the reproduction sense) even if two channel.

The question has arisen as to whether there is a psychoacoustically ideal recording method one should use when one knows that the subsequent reproduction will, in fact, be Ambiophonic. The other question considered here is whether this ideal Ambiophonic recording method is practical when compared with the usual two-channel recording techniques, including the optimized recording method for 5.1/7.1 surround reproduction so ably devised by Dr. David Griesinger and elucidated in several papers available on his web site [12] and the OCT system advocated by Głnther Theile [13].

This paper also suggests how the monitoring of Ambiophonic or even other recordings should be done during the setup, editing or mixing phases of the record production process.

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