CONFERENCE REPORT

CONFERENCE REPORT

798 J. Audio Eng. Soc., Vol. 61, No. 10, 2013 October

AES 52nd International Conference

Sound Field Control2–4 September 2013University of SurreyGuildford, UKSponsored by

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J. Audio Eng. Soc., Vol. 61, No. 10, 2013 October 799

Sound zone demonstrations inthe sphere loudspeaker array

The Austin PearceLecture Theatres,where the mainsessions were held

Conference chair Francis Rumseywelcomes delegates to Surrey.

Presenters and delegates from all over the world gathered atthe University of Surrey in the UK for a three-day confer-ence on sound field control, chaired by Francis Rumsey.

The University of Surrey is internationally known for its teach-ing and research in sound recording and psychoacoustics, aswell as its work in telecommunications, machine listening, andsignal processing. Based in Guildford, close to London’s majorinternational airports, its facilities provided an excellent base forthree days of papers, posters, workshops, and demonstrationsrelated to this growing field of audio research.

Introducing the conference, Francis Rumsey explained thatsound field control enables the active management of audiodelivered in an acoustical environment. Sophisticated signalprocessing and reproduction tools increasingly enable the engi-neer to tailor the sound field for specific applications, occu-pancy, or listeners’ requirements. This can include the creationof independent sound zones in listening spaces, the activecontrol of noise, personal communication systems, the electroa-coustic manipulation of auditorium acoustics, and the genera-tion of complex spatial sound fields using multichannel audiosystems. Sound field control can be used in automotive audio,consumer entertainment systems, mobile devices, aircraft inte-riors, concert halls, museums, and other public venues. All thisraises questions such as how sound fields can be controlledwithout detriment to sound quality, what the perceptual effectsof different methods of control might be, and how to optimizesystems for a specific quality of experience.

CONFERENCE REPORT

The 52nd Conference brought together engineers andperceptual scientists from the four corners of the earth toshare their research in the field, and to discuss the numer-

ous interactions between acoustics, signal processing, psychoa-coustics, and auditory cognition in this fast-moving field. It is likelythat we will see a number of real products based on these principlesappearing in our lives over the coming years, as sound becomesever more tailored to the complicated environments we live in.

During the opening session, the chair introduced his committee,all of whom had done sterling work in bringing the event tofruition. Søren Bech and Filippo Fazi had assembled a bumperpapers program, including a number of prominent invited speakersfrom the world research community. At over 350 pages, the confer-ence proceedings offers an impressive collection of papers on thelatest research in sound field control, demonstrating what a produc-tive area of activity this is today. Philip Jackson was in charge ofworkshops and demonstrations, showing how sound field controltechnology can be applied and what its perceptual implicationsmight be. Chris Hummersone, as publicity officer, had ensured thatall the right people found out about the event, using the latest socialmedia, while Khan Baykaner made sure that conference facilitieswere coordinated and working properly. Russell Mason acted as theconference treasurer. Roger Furness, AES Deputy Director, andHeather Lane from the UK office were on hand to ensure that dele-gates could register quickly and easily, and the conference ran verysmoothly as a result of their excellent work both before and duringthe event. Three student helpers from the university were on hand

to assist with the organization and the sound sphere demonstra-tions—Alice De Oliveira, Lucy Kolodynska, and Jack Wensley.

800 J. Audio Eng. Soc., Vol. 61, No. 10, 2013 October

The 52nd Conference committee: from left, Filippo Fazi (papers cochair), Khan Baykaner (facilities), Chris Hummersone (publicity), Russell Mason (treasurer), Francis Rumsey (chair), Søren Bech (papers cochair), and Philip Jackson (workshops and demonstrations).

Francis Rumsey (left) with Heather Lane and Roger Furness of AES HQ

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CAREFUL KEYNOTESThree influential keynote speakers had been invited to begin theproceedings of each day with inspiring overviews of the mainthemes of the conference. The first day dealt with engineering prin-ciples, the second with perception, and the third with creativeapplications.

Getting the conference off to a goodstart, Steve Elliott of the Institute ofSound and Vibration Research gave afascinating introductory keynote tuto-rial on the principles behind soundfield control. He looked back at theearly days of sound field rendering withSteinberg and Snow’s wall of loud-speakers, prefiguring wavefield synthe-sis by many decades. In a cleversynthesis of the histories and develop-ment of both active noise control andsound reproduction systems, heshowed both how they are similar andhow they are different. Although the principles are very similar inmany ways, in active noise control, he pointed out, most of thesummation and cancellation of waves that gives rise to theperceived result takes place in the acoustic domain. Steveconcluded by examining the applications of sound field controltechnology in personal audio systems, sound zones, and automo-tive audio, setting the scene for the packed program of morenarrowly focused papers to follow.

Professor Armin Kohlrausch of Philips Group Innovation andEindhoven University of Technology brought the audience up to

speed with trends in psychoacousticmodeling. In particular he posed aquestion about how far one can getwith perceptual models in relation tospatial audio and sound field control.Perceptual modeling, he showed, hadenabled restaurant owners to arrangetables optimally in crowded andacoustically poor spaces, for example.Models had shown that depending onthe position and head orientation ofdiners, significant differences in speechintelligibility could be observed.Including head movements in modelsis difficult, though, Kohlrausch

explained. When you make such movements yourself you can inter-pret the resulting changes in auditory cues, but getting models todo the same thing without voluntary control over the movementsis much more challenging. Elevation cues are more idiosyncraticthan horizontal ones, which presents another challenge to auditorymodels. In an attempt to address this, research has taken place intotemplate-based comparison of spectra to determine the locations ofsources. Armin concluded by pointing to a very useful publiccollection of auditory modeling tools, recently made available athttp://amtoolbox.sourceforge.net.

Opening the third day with a stimulating discussion of thecreative applications of sound field control, Frank Melchior of BBCR&D showed how the manipulation of sound objects was set torevolutionize broadcasting production and consumer entertain-ment. “What new user experiences can we deliver?” he asked,considering the gradual move toward object-based broadcasting.The idea behind this is to deliver media assets separately to the

audience, allowing adaptation, render-ing, and interaction at the user end.Audio content elements are transmit-ted separately from metadata describ-ing them. It’s not just an engineeringexercise, he said, but it’s really happen-ing in applications such as an object-based radio drama and football matchbroadcast. Echoing a theme developedquite strongly at the 52nd Conference,Frank emphasized that success here isnot about accurate physical correctnessin representing original sound fields,but about plausible experience. It’s notnecessarily about recreating reality but about designing alistener/viewer experience that is adapted to their context, task, andenvironment. Listeners might be allowed to choose their seat in aconcert hall, for example. How should one adapt reproduction fortablets, headphones, mobile devices? These are current avenues forhis research. Creative people want independent control over soundfield parameters that are not tied to physical models, it wasproposed. They might want to change the distance of a source with-out changing the reverberation, or change the Doppler shift with-out changing the location, or almost any other seemingly oddcombination one could think of. There has been a lack of innova-tion in mixing user interfaces in particular, even in software, saidFrank, and there is definitely room for change here. One needs tobe able to envisage an object-based mixing console with automa-tion of object trajectories. Although gesture-based mixing inter-faces have not proved particularly practical to date, he explained,there is certainly some mileage to be had out of novel soundcontrollers, one of which he demonstrated.

WONDERFUL WORKSHOPSFrank Melchior was also the chair of the first workshop entitled“The Interplay between Engineering and Perception in the Designof Sound Systems for Listeners.” On the panel were Jung-WooChoi, of the Korea Advanced Institute of Science and Technology(KAIST), Glenn Dickins of Dolby Laboratories in Sydney, andArmin Kohlrausch, keynote speaker of day two. Frank questionedeach speaker about their experience of the interplay between engi-neering and perception. Glenn Dickins noted that as time went onsometimes he felt he was becoming more of a conjuror or an illu-sionist with sound, because he had discovered that engineering

J. Audio Eng. Soc., Vol. 61, No. 10, 2013 October 801

Steve Elliott

Armin Kohlrausch

Panelists for the first workshop: from left, Armin Kohlrausch, Jung-WooChoi, Glenn Dickins, and Frank Melchior (moderator).

Frank Melchior

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does not trump perception. The psychology of the moment, heemphasized, often overwhelms the engineering solution.

Peter Lennox, one of the conference authors, suggested thatgaining greater clarity about what a sound field is in natural listen-ing might help us understand better what it should be in artificialterms. Learning spatial perception is important, it was suggested,and artificial or hyperreal constructs can also be learned. One ofthe problems in conducting good experiments in this multifacetedfield, suggested Armin Kohlrausch, is knowing whether one canreasonably ask subjects to pay attention to multiple constructs inone test. There is also the challenge of how to weigh the results toarrive at overall ratings or evaluations of the experience in ques-tion. In answer to this, Glenn Dickins suggested that waiting forthe answer about accurate multidimensional weightings of theelements of experience to build a complete model was something ofa waste of time. It’s better, he suggested to “grab some low hangingfruit” and move forward in small steps by trying things in sub-domains. Predictive models should try to help the engineer tomake small, informed steps forward. Focus groups and feedbackfrom them can be useful from a practical point of view, as opposedto formal experiments.

Boaz Rafaely, Ben-Gurion University of the Negev, moderated aworkshop entitled “Emerging Techniques, Applications, andOpportunities for Sound Field Control” on the second day. He wasjoined on the panel by Alain Berry of the Université de Sherbrookeand McGill University, Karlheinz Brandenburg of Fraunhofer IDMTand Ilmenau University of Technology, Gavin Kearney of theUniversity of York, and Emanuël Habets of the International AudioLaboratories, Erlangen.

Alain Berry pointed out that it is no longer possible to evaluatethe acoustic performance or quality of a dishwasher, say, using anumber. Sound field control and evaluation allows us to do this ina more sophisticated way using subjective evaluation. We can thenrelate computational acoustics to sound field control, evaluatingthe quality of sound objects. When approaching complicated prob-lems such as how turbulent boundary layers create noise in anaircraft, he said, we can now use arrays of loudspeakers and DSP tosimulate this rather than having to build accurate physical modelsand measure real sound fields.

Cinema owners now have the ability to decouple the soundreproduction array from the film sound format, said GavinKearney, allowing mixing engineers not to have to worry about thatany longer. With so many loudspeakers in modern installations,conventional panning tools are no longer practical, and material

can be rendered over numerousdifferent layouts. If you want to dothird-order Ambisonic mixingunder such circumstances thenconventional digital audio work-stations can’t cope in terms ofchannel count. The lack of stan-dardization of a common interme-diate sound field representationformat is hampering progresshere, he proposed.

Echoing a theme that had beenbuilding from a number of peopleduring the conference, SaschaSpors pointed out that adding lotsmore loudspeakers in sound repro-duction systems had not necessar-ily made things a lot better in

terms of quality. Karlheinz Brandenburg disagreed, suggesting thatsome demonstrations showed clearly noticeable phenomena withlarge arrays that simply can’t be achieved with something like 5.1surround. The issue seemed to center on how to more forward insophisticated sound rendering methods without sacrificing some ofthe simple, good features of sound that had been experienced inearlier days. There was a vigorous debate on the merits of reproduc-ing sound fields with high physical accuracy versus the art of “plau-sible experience” as Frank Melchior had put it.

In an attempt to move the debate out of the realm of the familiarand into areas of new possibility, Søren Bech pointed to a need fordetailed sound field control in novel fields such as medical applica-tions. We need to be able to keep patients isolated from the upset-ting noises in hospitals, for example. Houses are becoming morereverberant and need communications solutions. It was an impor-tant call to consider how this new area of technology can be appliedto improve the quality of life for people rather than simply to enter-tain them.

DRAMATIC DEMONSTRATIONSSet up in the studio facilities at Surrey were a number of demon-strations relating to the conference theme, provided by authorsfrom the conference and commercial sponsor, Yamaha. Thesehelped to show how sound field control can be applied in a range ofinteresting roles for personal listening, room acoustics control, andto aid the hard of hearing.

The Surrey Sound Sphere was a geodesic metal structure ofradius 1.9m used to support 72 Genelec 8020 loudspeakers. Thesewere individually controlled by software via MOTU soundcards. Theloudspeaker arrangement was the combination of a regular 60-element circular array mounted on the sphere’s equator and a 22.0surround format, which includes additional loudspeakers at eleva-tions of approximately −30°, +30° and +90°. The system wasinstalled in the relatively dead Studio 2 for sound field controldemonstrations of several different methods of forming personalsound zones.

A compact 16-channel loudspeaker array had been developed incollaboration between the University of Southampton and theUniversity of California, San Diego. The real-time DSP engineallowed for multizone sound reproduction and multichannelcrosstalk cancellation for binaural audio and for beamforming withlistener tracking.

A superdirective loudspeaker array for improving TV audio for thehearing impaired had been developed at the Institute of Sound andVibration Research, University of Southampton. This device had beendesigned to generate a highly directive sound beam for spatially

Panelists for the second workshop: from left, Alain Berry, GavinKearney, Emanuël Habets, and Karlheinz Brandenburg

Boaz Rafaely chairs theworkshop on emergingtechniques.

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localized audio enhancement, improving the intelligibility of audiomaterial delivered to listeners with reduced hearing capabilities.

In addition to the engineering demonstrations, there was alsothe opportunity to participate in perceptual evaluation of interfer-ing sound zones, such as might occur during simultaneous repro-duction of television and radio program material within a singleacoustic environment. This included demonstrations of listeningtests and the opportunity to listen to a range of stimuli that wererepresentative of interfering sound zone situations. It allowedattendees to experience the potential problems that might beperceived when using these systems, and how various factors suchas program material choice, system performance, and listener taskaffect the perceived result.

Yamaha Commercial Audio had set up a complete reverberationenhancement system in Studio 1, and during an interesting spon-sor seminar Ron Bakker explained the history of reverberationenhancement. He showed how the early Royal Festival Hall system,known as Assisted Resonance, amplified the natural reverberantfield of the hall by using narrow-band resonators housing micro-phones, connected to loudspeakers strategically placed. Other in-line systems used artificial reverberation between microphones andloudspeakers. Yamaha’s AFC3 is the 3rd generation of hybrid regen-erative acoustic enhancement systems since 1987, using FIR filter-ing and spatial averaging techniques to achieve system stabilitywith a small amount of independent channels. The hybrid part ofthe AFC3 system consists of a 4-channel convolution reverberatorthat is used to adjust the existing acoustic response of the room,

rather than replacing it, which is the domain of the ‘in-line’systems. The system shown in PATS Studio 1 was a small single-module system that enhanced the diffuse reverberation field in theaudience area as well as on stage, using an AFC3-FIR DSP corewith four DPA 4060 omnidirectional microphones, twelve IF2108loudspeakers, and Dante based audio distribution. The system wastuned by Takayuki Watanabe of Yamaha’s Spatial Audio SystemGroup in Japan and was visited by almost all the delegates through-out the conference for a closer look and listen.

POWERFUL PAPERSThe main backbone of the conference was provided by nine paperssessions on key aspects of sound field control. These were comple-mented by a busy poster session preceded by a preview duringwhich authors had a chance to promote their poster to the assem-bled audience. Overall, 37 papers were given at the 52nd Confer-ence, bringing together some of the most notable researchers inthe topic area.

The sessions on sound field control theory and applicationsincluded papers on source-width extension, the design of sourcearrays, determination of sound field control, reproduction of flightrecordings, scene analysis from compact microphone arrays, andacoustic element approaches. In the poster session that followedtopics ranged far and wide, including real-time sound field trans-mission, multizone audio reproduction, the uncanny valley ofspatial voice, and the relaxation effects of binaural phenomena.

On the second day, two sessions on psychoacoustics followed

Top row, from left, listening to sound zones inthe sphere; recreating a multisource spatialsound scene with a GPU accelerator; a real-time listening test on sound zone interference.Bottom row, from left, delegates discuss theirexperience in the sphere; Ron Bakker ofYamaha explains reverberation enhancementwith Tim Harrison (inset) playing variousmusical instruments. DEMONSTRATIONS

Armin Kohlrausch’s keynote. Here welearned, among other things, aboutthe perceptual optimization of loud-speaker selection for the creation ofpersonal sound zones, as well as aboutthe prediction of acceptability of audi-tory interference. Peter Lennox tookthe audience into new territory byconsidering cognitive maps in spatialsound, proposing that it’s importantto learn about the way that the brainconstructs its perception of soundfields. Anthony Tucker added to thecontroversy about whether one shouldalways aim for physical accuracy insound field reconstruction by reveal-

ing the “dirty little secret” that it often helps to introduce someerrors rather than control the fieldtoo precisely.

Systems to create sound zones weredescribed in five papers after lunch,looking into subjects such asplanarity, the effect of reflections,scattering with a head and torso simu-lator, control strategies for a car cabinsystem and the design of a superdirec-tive array. This was followed by asession on transducers, array design,and beam forming, including MarkPoletti’s presentation on the design ofa prototype variable-directivity loud-speaker for improved surround repro-duction, and Jiho Chang’s

presentation on theadvantages of double-layer arrays.

Wednesday morningbrought the topic ofsound field control formultichannel audio,following FrankMelchior’s keynotelecture. Mincheol Shinspoke about the controlof velocity for sound fieldreproduction, and AngeloFarina introduced“Spatial PCM Sampling”as an alternative methodfor sound recording andplayback. After the breakwe got into roomacoustics control, look-ing at a Danish low-frequency test facilityand the design of activeacoustic absorbers. BoazRafaely presented aninvited paper togetherwith Hai Morgensternand Noam Shabtai, on

sound field control in enclosures by spherical arrays.To wrap up the proceedings the final afternoon session on wave-

field synthesis was opened by Karlheinz Brandenburg, who spokeon the future of intelligent multichannel signal processing in audioreproduction systems. Dylan Menzies followed by introducing effi-cient 2.5D driving functions for quasi-wavefield synthesis, andfinally Keunwoo Choi discussed the process of multichannel toWFS upmixing using sound source separation.

SPECTACULAR SOCIALIZINGOne of the main reasons people go to conferences is to meet othersworking in the same field, and the 52nd provided plenty of opportu-nities for good social interactions between the delegates. Manywere staying on site in university student accommodation, so therewas a good sense of community during the three days of the event.

A buffet supper on the first evening followed seamlessly from theposter session, allowing an informal atmosphere in which peoplecould either renew old friendships or forge new ones, continuingthe discussions they might have started around one of the posters.The conference dinner on the second night was held in GuildfordCathedral Refectory, during which an excellent three-course mealwas served. The outstanding weather, which was warm and sunny,allowed delegates to enjoy the outside air before the dinner and in-between conference sessions, taking their lunch outside or justrelaxing before another heavy period of concentration. There wasan almost endless supply of coffee, tea, juice and cakes, courtesy ofthe university’s catering operation, to keep everyone well fueled forthe day’s work. Many returned home a few pounds heavier, it seemslikely.

SUMMARYAfter a busy three days the assembled company departed withnumerous new ideas and a much better overview of the topic ofsound field control. Many said that it had enabled them to seebeyond their own narrow slice of the subject, and to make con-nections between the engineering and perceptual domains. Ofthe key themes raised during discussions at the conference, thechair summarized two as most important. First, that context iseverything—it is possible to do almost anything you like with anarray of loudspeakers and some clever signal processing, but themeasure of success depends on the task in hand and what isappropriate for one situation may be entirely inappropriate foranother. Second, the boundary between illusion and physicalaccuracy is a hard one to cross successfully. The closer we get to

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804 J. Audio Eng. Soc., Vol. 61, No. 10, 2013 October

Peter Lennox on cognitivemaps in spatial sound

Jordan Cheer waxes lyrical on car cabin personal audio systems.

Richard Furse discusses a poster.

Joe McCabe of Bose asks a penetratingquestion.

Mark Poletti on variabledirectivity loudspeakers

physical accuracy in sound field control, the more in danger wemay be of falling into the “uncanny valley” where the incon-gruities between perception, expectation, environment, andacoustics become more keenly noticed.

CONFERENCE REPORT

Editor’s note: You can download papers from this conference fromthe AES e-library at http://www.aes.org/e-lib/

Delegates enjoy a splendid meal in Guildford Cathedral Refectory.

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Francis Rumsey hands out certificates of appreciation to variousparticipants, together with bottles of local English beer for them tosample.

Enthusiastic delegates swap business cards during a break.Guildford Cathedral refectory, location of the conference dinner