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AES

Audio Engineering Society

24th International Conference on Multichannel Audio
June 26-28, 2003, Banff, Canada

 

SURROUND AMBIOPHONIC RECORDING AND REPRODUCTION

by Ralph Glasgal

ABSTRACT

Ambiophonics, Panorambiophonics, and Periambiophonics are related surround sound paradigms that reliably deliver up to full 360-degree spherical localization for both direct and ambient sound via two, four, or six DVD/SACD/MLP/DTS/Dolby/ADAT coding/media channels. They reproduce old or new, standard, 2, 4, 6, or ITU 5.1-channel music discs with unprecedented spatial realism and binaural-like localization accuracy via direct sound radiating front/rear/overhead stage-producing Ambiopoles and virtually any desired number of ambience surround speakers.  Alternatively, superior acoustic recordings can be made using the described Ambiophones (or using algorithms if fabricated) to capture images of startling depth and presence for music in the round, 3D movie sound tracks, virtual reality, or electronic music soundscapes.  Six-channel Periambiophonics adds elevated direct sound to the fully spherical hall ambience vectors already provided by basic Ambiophonics which drives essentially any number of hall ambience speakers regardless of their positions.  All the versions of surround Ambiophonics easily deliver a “you-are-there”, psychoacoustically correct, home listening experience, via home theater media, albeit best limited to one or two listeners.

 

 

INTRODUCTION

Ambiophonics is a comprehensive sound recording/reproduction methodology, that like or unlike Stereophonics,  Ambisonics, THX 5.1 or Wavefield Synthesis, prescribes hardware/software that scrupulously insures that the well known tenets of human binaural hearing [Appendix 1] are rigorously catered to so as to achieve psychoacoustic and physiological verisimilitude for one or two home listeners/viewers who seek and value “you-are- there” realism.

Ambiophonics combines crosstalk-free speaker pairs (Ambiopoles), surround speaker ambience derived from measured hall impulse responses via a convolver (Ambiovolver) and room/speaker correction/treatment to generate a binaurally correct sound field similar to wavefield synthesis. Ambiophonics creates a concert hall stage and hall from just two media channels as found on CDs, MP3s or LPs feeding a single Ambiopole. Panorambiophonics requires four media channels as provided by multichannel DVDs or SACDs  each pair feeding its own Ambiopole.  Periambiophonics uses six media channels as in DVD-A, DTS-EX, etc. feeding three Ambiopoles.  In each type of system additional hall ambience surround speakers may also be driven via a single Ambiovolver and this is strongly recommended where music is concerned.

A single Ambiopole in front easily produces a stage of about 160° in width. A single Ambiopole to the rear of the listener produces a similar rear stage width.  A remarkable property of the Ambiopole software we have developed is that when both front and rear Ambiopoles are working together, they blend and the front and rear stages widen to the full 180°. Thus, 360° of horizontal localization becomes easily attainable for recordings made with Ambiophones or synthesized. A third or even more Ambiopoles can be elevated over the front and/or rear Ambiopoles to add full width stages high in the air and again there is vertical fill between the stages although the extent of this phenomenon has yet to be fully investigated.

The most basic Ambiophonic theory [See Ref. list] is meant to allow previously recorded two channel media such as CDs, MP3s, and LPs to be reproduced without the well known limitations of the traditional 60-degree stereo triangle [Appendix 1], to deliver an uncompromised full width direct sound stage from two center-front speakers (an Ambiopole) and to provide real diffuse but still directional hall ambience to almost any number or location of surround speakers including elevated speakers.

It became obvious in the early development of Ambiophonics that existing stereo microphone techniques could be revised to produce better two channel recordings. Thus, on the recording side, the Ambiophone, a novel, baffled microphone arrangement, takes advantage, when recording, of the knowledge that the playback will be Ambiophonic. (not via the stereo equilateral triangle although Ambiophone recordings are actually backward compatible and sound quite normal in standard stereo) The Ambiophone also assumes that both the amplitude and the directional attributes of the early reflections and reverberant tails of the hall will be properly directed to the appropriate frontal Ambiopole and surround speakers. (Indeed, this is possible even in the case of non-Ambiophone recordings if the recorded or added reverb, unfortunately mixed into the direct frontal sound, is not too intrusive.)

After a brief review of the basics, this paper is devoted to advanced versions of Ambiophonics which take into account the 5.1, 6.0, 7.1, Dolby/THX and DTS coding/media/speaker arrangements. Special matrix coding developed by Robin Miller of Filmakers Studios [ref 17] allows two or four media channel Ambiophonic/Panorambiophonic recordings to be played back via the 5.1 speaker arrangement with clearly superior, if not ideal (compared to Ambiophonic) verisimilitude over such ITU systems. In reverse, standard 5.1 discs may also be played Panorambiophonically (described in detail below) in a manner analogous to the Ambiophonic playback of ostensibly stereo CDs or LPs, but, in this case, using front and rear Ambiopoles and surround ambience speakers driven by a hall impulse response Ambiovolver. Most 5.1 movie and music DVDs or music SACDs reproduce exceptionally well this way especially when compared with the ITU 5.1 standard speaker arrangement. [Appendix 1] Panorambiophonics, described below, uses four channel coding/media such as Dolby, DTS, SACD, or DVD-A to deliver an easily localizable 360-degree direct sound stage as in movies, or, for concerts, a very wide front stage that, if in a hall, automatically includes horizontal 360 degree hall ambience. A four channel recording mic, the Panorambiophone, has been designed to make such recordings. Only four speakers (two Ambiopoles) are used in Panorambiophonic reproduction to reproduce all horizontal plane direct sound and horizontal hall ambience with full circle normal binaural localization physiology. Where the direct sound recording has been made in a dry or small studio, it is possible to enhance the reproduction of these front and rear direct sound fields by adding ambience surround speakers driven by an hall Ambiovolver as in standard Ambiophonics.

Periambiophonics adds a third elevated Ambiopole to Panorambiophonics to provide for a full direct sound stage in all dimensions including some height. The elevated Ambiopole can be used for direct sound reproduction or ambience. In the latter case this allows a concert-hall direct sound performances to be recreated in a home with just three speaker pairs and no surrounds.. Using three direct sound Ambiopoles allows movies, virtual reality, games and soundscapes to sound more like the live experience. Furthermore, Periambiophonics can combine six- channel Periambiophone recording, and the front, rear, and elevated Ambiopoles, with an Ambiovolver to add virtually any desired number of surround speakers so as to deliver physiological verisimilitude of a concert hall experience that also includes rear or overhead direct sound sources to a home listener via standard DVD/SACD media. Clearly, both Panorambiophonics and Periambiophonics are well suited to capture, create and reproduce 3D electronic music or virtual reality projects.

This paper reviews the theory, techniques, and features, of the hardware and software required to make these various kinds of Pan/Peri/Ambiophonic recordings and to reproduce these as well as stereo CDs and the various multichannel surround media.

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