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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.

6. TESTED APPLICATIONS

Numerous recordings have been made with each PanAmbiophone during its evolution, ranging over many musical genres (e.g. opera,, orchestral, organ, big band, brass quintet, bluegrass in a club, etc.) and ambient sounds (e.g. playgrounds, parades, etc.). In many cases, additional microphones representing INA [29], OCT, and soundfield arrays have been recorded simultaneously for comparison, such as for the multiformat demonstration led by the author at the AES 24th International Surround Conference in Banff, Canada, June 2003 [30,21]. For all demonstrations and reported results, no equalization, level compression, or other effects were used. Results have been more or less gratifying, leading to further improvements of both the PanAmbiophone and the technique for using it.

The discovery of the need for different polar characteristics for outdoor and indoor use has been discussed. The latest PanAmbiophone, designed for staged performances inside acoustic spaces, has been used for recordings of an oboe trio in a studio, chamber orchestra (10 players) in an auditorium, choir in a church, and orchestra in a hall with increasing success. Each of these sessions is briefly described:

  1. In a 400 seat auditorium with a 10 piece chamber orchestra, the PanAmbiophone was placed at about the critical radius of the room (approx. 5m) with players arranged within a relatively wide 100° recording angle. The Miller PanAmbiophone for 2D & 3D surround recording reproduction stage was equally wide using a PanAmbio speaker layout (Fig.2, Appendix). Clinging to many years of traditional stereo and surround recording experience, this early experiment erred in too close a placement of the new microphone and so, with front and back channels in calibrated balance, proved overly dry. However, in post, the front-back balance was “fixed” by independent control of the front and back microphone pairs. Since it favors frontal sound (much as a cardioid increases working distance over an omni), the new microphone should have been used somewhat beyond the critical radius. A byproduct is that the array can be suspended above audience (or camera) sightlines.

  2. The oboe trio in a 500m<³> soundstage with acoustics set for “live” was recorded beyond the critical radius (at 3m cf. 2.5m) with the trio subtended within a 100° recording angle. Replay in PanAmbio preserved this angle (in stereo or 5.1 it was, of course, limited to 60°) and resulted in good balance as calibrated between direct and early reflections from all around the space. The recording exhibits clarity and intimacy and is popular with recording engineers at demonstrations. Upon hearing a replay in the control room but sensing that the sound replicated the soundstage, a musician involved exclaimed “Finally, it’s my sound.” Listeners who represent consumers, after hearing the piano played in the soundstage, then hearing the recording in the control room, report “It sounds like that room, not like this room.” – which can be interpreted as meeting the objective of high spatial definition.

  3. For the 2nd anniversary concert of 9/11 in a church at Ground Zero in New York City (see Fig.20), the Rutter Requiem was performed by the professional chorus Seraphim and eight instrumentalists within a recording angle of 90° of the PanAmbiophone placed beyond the critical distance at 6m. Microphone levels were calibrated using band-limited pink noise. (While artistically quite satisfying, high RF interference from countless security radios marred the recording – the problem has been rectified since.) The very moving music, accompanied by the tolling of a large bell outside for each person killed, was faithfully reproduced – the choir, ensemble, and the church’s acoustics in precise balance and tonally natural.

  4. Columbia University Chapel in New York City was the venue for the Greenwich Village Orchestra playing Beethoven’s 9th Symphony (see Fig.1). 80 players, 60 choristers, and 4 soloists were recorded beyond the critical distance (4.5m from soloists) within a wide 120° recording angle. Played in PanAmbio, the soprano and bass-baritone are heard nearly that wide – about 110° apart. The chorus, positioned deep and underpowered cf. the orchestra to the live hearer, is reproduced exactly so. However, in the mix, both the ambience and resonance of the male voices was improved by adjusting the back-to-front balance. The orchestra and chorus and their conductors have expressed praise for the artistic integrity of the recording. (Recording engineers agree, but must hear beyond the notquite-commercial quality of the semiprofessional performance, recorded live before a student audience – with cell phones.)

Due to the 120° front stage and 240° back, the new PanAmbiophone trades absolute directionality for good balance and ease of use inside. Outside, as expected, 2D space is warped when played in PanAmbio, as the 120° front stage becomes 180° in front of the listener, and the 240° back stage becomes 180° in back of the listener. While not exhaustively measured as of this writing, suffice it to state subjectively that it works as designed: a passing parade, marching in a straight line, was warped into a noticeable V shape, starting from back-right and ending back-left. On a playground, kids playing in a circle are heard to speed up around back and slow down in front. The original PanAmbiophone would have preserved these angles within ±5° around 360°, as plotted above. The choice of pattern is up to the recording engineer.

7. SUBJECTIVE RESULTS, FUTURE WORK

Anecdotal comments by the musicians involved and by representatives of consumers at demonstrations are briefly mentioned in the above section. Some expressed themselves with eye-popping, jaw-dropping, and requests for owning their own Ambiophonic system. A small minority report they cannot hear the wide stage or localize sources within it – Ambiophonics researchers believe there is some learning required, similar to acquired conditioning to conventional stereo/5.1.

Engineer-auditioners at the AES 24th Surround Conference in Banff, Canada, June 2003 heard recordings made with the new PanAmbiophone and generally commented positively [21], especially about PerAmbio 3D over just 10 small speakers [19,20,21]. Some report a sensation of “pressure” near the Ambiophonic mid-plane, only on which crosstalk cancellation occurs. Hybrid PerAmbio 3D is more forgiving in this regard, presenting credible envelopment for a broad listening area that, in Filmaker Technology’s listening room, accommodates six persons (Appendix Fig.C). Still, critical listeners would want to be at the Ambiophonic “focus” for the most accurate sound.

For future experimentation and demonstration, it is hoped that a record label will permit a simultaneous recording by the author using the PanAmbiophone for comparison of the producer’s normal recording with PanAmbio 4.0 and PerAmbio 3D/2D. Both of these “flavors” are 5.1-compatible directly and can be released on any “shiny disc” media. PerAmbio 3D/2D requires 6-channel media e.g. DVD-A, SACD, or DTSES Discrete CD. Also planned are refinements to the PanAmbiophone structure and equalization for use in commercial recording, movies, or broadcast.



Fig.20 – PanAmbiophone at right recording 9/11 requiem near Ground Zero, New York, in 5.1-compatible PanAmbio surround.

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