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Audio Engineering Society
Convention Paper

Spatial Definition and the PanAmbiophone microphone array
for 2D surround & 3D fully periphonic recording

Robert E. (Robin) Miller III ©2004
FilmakerStudios, Bethlehem, Pennsylvania 18018, USA

Presented at the 117th Convention
2004 October 28-31 San Francisco, CA

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.

2. THE “FAMILY” OF AMBIOPHONICS

Ambiophonics embodies both prior and new art in the pursuit of lifelike audio. Briefly, the three “flavors” are:

  • Ambiophonics (“Ambio”) – 2-channel recordings, including many originally intended for stereo or binaural, with (optional) hall convolution [23]) – illustrated in Appendix;
  • Panor-Ambiophonics (“PanAmbio” [24]) – 2D surround from 4-channel recordings (ITU 5.1- compatible with silent center) – illustrated in Fig.2 and Appendix Fig.B;
  • Periphonic Ambiophonics (“PerAmbio” 3D (with height) full sphere surround (5.1/6.1-compatible from 6-channel encoded recordings Pat. pending) – illustrated in Appendix Fig.C, [19,20,21].

All three can be augmented with hall impulse response (IR) convolution [25,26], although both PanAmbio 2D and PerAmbio 3D record surround directly, correctly positioning hall ambience and sources at side, in back, and up/down in 3D. Information on all Ambiophonic approaches may be found in the Appendix, on this web site, and at the Filmaker Technology web site.

Spatial resolution/definition is addressed in all Ambiophonic approaches to stereo, 2D surround (“PanAmbio”), and 3D (“PerAmbio”). All preserve HRTF-related information captured in the recording and reproduce it using crosstalk-cancelled speaker pairs (stereo dipoles) that are closely spaced and in the general direction least confusing to the pinna. Over speakers, Ambiophonic reproduction works like “virtual headphones,” reproducing binaural replicas of the original venue sounds, but more comfortably and with no inside-the-head sounds. In ITU 5.1, directionality (therefore tonality) is distorted, whereas in PanAmbio 4.0 it is precise within ±5° using double stereo dipoles front and back. A PanAmbio recording is made with a special microphone array (described below), has a lifelike quality, plays compatibly on 5.1/6.1 speaker layouts, and may if desired incorporate spot microphones and center channel processing.

Ultimately, reproduction with height is required to approach live 3D hearing, where arrivals from above and below also contribute to tonality due to individual pinna filtering. As said, in acoustic spaces, performers (musicians, vocalists, Foley artists, etc.) “play” the entire sphere of periphonic sound as extensions of their instruments, for which the integration of many headtimed and pinna-filtered arrivals define tonality also for the listener in the same space. Having learned this complex interplay from experience, individual listeners now expect the same interplay as their personal standard for live hearing – and recognize, in the absence of lifelike spatial definition, that it is “only a recording.” So the ultimate step in realistic audio is full-sphere 3D.

2.1. PerAmbio 3D/2D – decoderless 5.1 or 3D

The ultimate in spatial definition is 3D (with height) reproduction, where the listener is at not just the center of a circle as with 2D surround e.g. 5.1, but at the center of the sphere of human hearing. “PerAmbio 3D/2D” (Pat. pending) [19,20,21] combines Ambiophonics and a modified Ambisonic soundfield, for the ability of each system in reproducing front stage and ambience, respectively, and delivers it on common 6-channel media (DVD-A, SACD, DTS-ES Discrete CD) to be replayed either on ITU 5.1/6.1 layouts without any decoder, or (from the same disc) in full 3D by adding a decoder and four or five or more speakers placed in positions programmed in the decoder. A “mode” for decoderless 5.1 2D mapping is chosen by the recording engineer, possibly changed in post-production, and selected upon replay by the user (automatically in metadata?). Alternatively or in combination to enhance ambience, hall sound may be convolved from hall impulse responses, either by producer or user.

The PerAmbio 3D/2D speaker layout (see Appendix Fig.C) is fully backward-compatible with 5.1 recordings by the listener simply repositioning back 26% of the speaker diameter, where speaker angles match the ITU standard. Height and surround speakers may be flexibly positioned and their coordinates programmed in the decoder. For other than the most critical music listening, or for movie-watching in 3D, up to six listeners can be accommodated in PerAmbio 3D/2D’s broad listening area.

Recorded using a hybrid microphone based on the PanAmbiophone, below, PerAmbio 3D/2D is a multiformat-compatible system that allows performances to be preserved, and both producers’ and users’ libraries to have greater future value in a future 3D audio world.

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