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Audio Engineering Society
Convention Paper

Transforming Ambiophonic + Ambisonic 3D Surround Sound to & from ITU 5.1/6.1
Robert E. (Robin) Miller III ©20031

Appendix A: Requirements for PerAmbio 3D

To fully realize 3D playback requires stringent listening acoustics [20].  Distribution formats can be DTS-CD, DVD-V, DVD-A, SACD, or multi-channel broadcast using AAC of the MPEG4 standard.

Requirements for 6.1.10 Playback are:

  • Acoustically treated room with RT less than recording venue and symmetrical layout of the speaker sphere with listeners seated at the center at less than the acoustic room radius;

  • Two high quality speakers (especially identical phase response) FL & FR plus eight satellite-grade for total of 10 speakers plus subwoofer(s);

  • Universal DVD/CD player or ATV receiver with 6 full range analog channels or DTS bitstream;

  • A "smart" decoder that detects a flag in metadata to select automatically the transformation mode, obviating user inconvenience and error;

  • Crosstalk-canceller, ideally based on impulse response of speakers used;

  • Bass manager accommodating 10+ speaker feeds;

  • 2 higher and 8 lower power amplifiers for total of 10 channels of power amplification (note crosstalk cancellation requires higher than normal power);

  • Calibration of channels at listening position within ádB using an SPL meter and filtered pink noise.

Any number of listeners not near any one speaker can enjoy the sense of enveloping 3D, although only one or two on the median plane will hear accurate front localization.  Mixes intended for ITU 5.1 to 7.1 can be enjoyed by simply moving back 26% of the speaker diameter.  2-channel stereo can be enjoyed by feeding the 8 ambience channels convolved with hall impulse response.  All 6.1.10+, 5.1, and 2-0 programs will reproduce up to 120° wide front stage localization for one or two listeners on the žambiophonic plane.Ó

Appendix B: Ambisonics Very Briefly

In 1985, Gerzon [12] approached wavefield synthesis mathematically using an omni (W) and three coincident bi-directional microphones aimed forward, leftward, and upward (X, Y, & Z).  The array can be realized using individual microphones, or packaged as in a SoundField microphone.  Four recording channels (B-format, first order) supply a unique hypercardioid signal (see Fig. 14) to each of any number of speakers

sA,E = 0.5W + cosAncosEnÔX + sinAncosEnÔY + sinEnÔZ

Ambisonics can be created by assignment, say of monaural dialogue or effects using a 3 dimensional pan pot much as 5.1 can by a 2-dimensional one.  B-format (4 channel) stems of music or ambient sound effects can be combined to a 4 channel Ambisonic mix.

AmbisonicsŪ theory fails in many situations where wavefronts are still spherical - reverberation in smaller spaces and direct sound closer to sources; farther and direct sound is swamped in ambience.

For more distant plane waves and pan-pot simulation where the pressure channel W is not uncorrelated with velocity components X, Y, & Z, Ambisonics suffers from lack of spaciousness, similar to coincident M-S.  Good spatial impression seems to require spaced microphones, such as the Ambiophone (baffled, pinna-less sphere), which when played Ambiophonically imparts wide, accurate front stage localization.  Combined, PerAmbio exceeds in 3D envelopment + frontal imaging + spatial impression.


Fig.14.  Ambisonics in essence has žaimedÓ in the direction of each speaker a hypercardioid microphone (directivity=0.6667), derived from coincident omni and bi-directional microphones.  The žpush-pullÓ of out of phase information in opposing (isotropic) speaker pairs synthesizes the wavefield for plane waves from distant sources.  The experimentally determined minimum for first order 3D Ambisonics is eight speakers, with incremental improvement with 12 and 24 speakers.

REFERENCES

1.  ITU-R BS.775.1: žMultichannel Stereophonic Sound System With and Without Accompanying PictureÓ (Geneva, 1992-4).

2.  R Miller, žCompatible PanAmbiophonic 4.1 and PerAmbiophonic 6.1 Surround Sound for Advanced Television - Beyond ITU 5.1,Ó SMPTE 144th Technical Conf. & Exhibition, Pasadena CA USA, October 2002

3.  Fabio Bozzoli, Enrico Armelloni, Emanuele Ugolotti, Angelo Farina, žEffects of the Background Noise on the Perceived Quality of Car Audio Systems,Ó Proceedings of AES 112th International Conv., Munich, Germany 2002.

4.  R Miller, žContrasting ITU 5.1 and Panor-ambiophonic 4.1 Surround Sound Recording Using OCT and Sphere Microphones,Ó Proceedings of AES 112th International Convention, Munich, Germany 2002, preprint #5577.

5.  F. Rumsey, T McCormick, žSound and Recording,Ó Focal Press, ISBN 0-240-51680-X, pp 382-388

6.  G. Theile, žNatural 5.1 Music Recording Based on Psychoacoustic Principles,Ó Proceedings of the AES 19th International Conf., Schloss Elmau, Germany, June 2001.

7.  R. Miller, žPerAmbiolating 360°: Panorambiophonic 4.0Ó multichannel evaluation DTS-CD, žPerAmbiolating 360°: Companion ITU 5.0,Ó multichannel evaluation DTS-CD, with print insert, žSurroundÓ pages, www.filmaker.com.

8.  J. Wuttke, žGeneral Considerations on Audio Multichannel Recording,Ó Proceedings of AES 19th International Conf., Schloss Elmau, Germany, 2001.

9.  H. Wittek, O. Neumann and M. SchĒffler, C. Millet, žStudies on Main and Room Microphone Optimization,Ó Proceedings of AES 19th International Conf., Schloss Elmau, Germany, 2001.

10.  D. Griesinger, žThe Psychoacoustics of Listening Area, Depth, and Envelopment in Surround Recordings and Their Relationship to Microphone Techniques,Ó Proceedings of AES 19th International Conf., Schloss Elmau, Germany, 2001.

11.  G. Theile, žOn the Naturalness of Two-Channel Stereo Sound.Ó  J. Audio Eng. Society, Oct. 1991.

12.  M. Gerzon, žAmbisonics in Multichannel Broadcasting and Video,Ó JAES Vol. 33 No.11, 1985, pp 859 - 871T.

13.  R. Glasgal, žAmbiophonics: Achieving Physiological Realism in Music Recording and Reproduction,Ó Proceedings of AES 111th Convention, preprint 5426.

14.  Farina, R. Glasgal, E. Armelloni, A. Torger, žAmbiophonic Principles for the Recording and Reproduction of Surround Sound for Music,Ó Proceedings of AES 19th International Conf., Schloss Elmau, Germany, 2001.

15.  R. Miller, žAmbiophonic Demonstration: AES Bavaria 2001Ó 2-chan. CD with print insert, and PS online Ambio demonstration, žSurroundÓ pages, www.filmaker.com.

16.  M. Gerzon, žOptimal Reproduction Matrices for Multispeaker Stereo,Ó AES 91st Conv. 1991, New York, preprint 3180.

17.  T. Holman, ž5.1 Up and Running,Ó Focal Press, ISBN 0-240-80383-3.

18.  ATSC Document A/52A žATSC standard: Digital Audio Compression (AC-3), Rev. AÓ 8/21/2001, www.atsc.org/

19.  B. Blesser, žAn Interdisciplinary Integration of Reverberation,Ó AES 111th Conv. NYC 2001, preprint 5468 as presented.

20.  žMultichannel surround sound systems and operationsÓ - AES Technical Document ESTD1001.0.01-05

Author

Robin Miller is a member of AES and SMPTE, musician and orchestrator, broadcast engineer, teacher, and 53 award-winning producer.  As an audio engineer, he has more than 40 years experience in music recording and mixing 300 films and television specials plus countless live broadcasts.

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