aes23 int ernational conferenceaes23rd int ernational conference signal processing in audio...

AES23rd INTERNATIONALCONFERENCE

Signal Processing in AudioRecording and Reproduction

846 J. Audio Eng. Soc., Vol. 51, No. 9, 2003 September

Marienlyst Hotel, HelsingørCopenhagen, Denmark

May 23–25, 2003

Jeff Bier, keynote speaker Kees Immink, AES president Per Rubak, conference chair

J. Audio Eng. Soc., Vol. 51, No. 9, 2003 September 847

The town of Helsingør is situated on the north-east corner of Denmark overlooking the nar-rowest part of the Øresund, a busy waterwaythat links the North Sea to the Baltic Sea. Thehistory of the town can be traced back to 70AD, and the area contains a number of impres-

sive royal castles dating from as early as 1100 AD. Againstthis historic backdrop, from May 23rd to the 25th, the AESheld its 23rd International Conference, Signal Processing inAudio Recording and Reproduction, covering some of thevery latest techniques in signal processing for audio.

The conference committee worked hard to ensure thatthe conference was a success. Per Rubak as conferencechair and Jan Abildgaard Pedersen and Lars Gottfried Jo-hansen as papers cochairs drew together over 20 excellentpapers covering many aspects of signal processing. Theywere ably assisted by Knud Bank Christensen, conferencesecretary, Eddy Bøgh Brixen, facilities chair, and SubirPramanik, treasurer.

The conference was held in the Marienlyst Hoteland Conference Center, overlooking the Øre-sund and the shore of Sweden across the wa-ter. Included in the program was a mix ofpapers sessions, demonstrations, andsocial events. In addition to these, therewere plenty of opportunities for thedelegates to discuss hot topics and tocontribute to the global communitythat is the Audio Engineering Society.

OPENINGConference Chair Per Rubak opened theproceedings by giving an overview ofthe wide range of applications that werepossible through the increasing use andavailability of digital signal processingtechnology. He reflected on the great

amount of progress that has been achieved in this area sofar and hoped that the conference would provide inspirationfor further progress.

AES President Kees Immink thanked the hard-workingcommittee for producing a successful conference. He statedthat it was an odd place to hold an audio event, as the reign-ing king of Denmark had introduced a tax on the Sound in1429. He was, of course. talking about the tax levied onships passing through the Øresund (Sound). He encouragedthe delegates to take advantage of the conference format byconferring with each other to gain from the international ex-pertise and knowledge of those present.

SIGNAL PROCESSING HARDWAREThe keynote speech, given by Jeff Bier of Berkeley DesignTechnology, was an overview of trends in signal pro- ➥

J. Audio Eng. Soc., Vol. 51, No. 9, 2003 September848 J. Audio Eng. Soc., Vol. 51, No. 9, 2003 September

cessing hardware. He covered different types of signal pro-cessing hardware that may be used for audio purposes, con-sidering not only the processing capability but also thepractical and commercial aspects of each option. He ex-plained that one of the main decisions that has to be madewhen choosing a suitable processor is the compromise be-tween efficiency and flexibility, and that the optimumchoice can differ greatly depending on the specific applica-tion. Bier summarized a number of important trends in theconsumer marketplace—including the convergence of mul-timedia applications into other devices and the increasingconnectivity between devices. “These are interestingtimes,” he stated, because of the increasing ubiquity of dig-ital audio, the change in emphasis from hardware to soft-ware, and the capabilities and challenges of increasing con-nectivity. He forcast that we will see a great increase in theuse and development of the techniques discussed at theconference.

SIGNAL CONVERSIONThe afternoon session of the first day started with a paperby Søren Nielsen and Thomas Lund of TC Electronics, fo-cusing on the topic of overload in signal conversion. It wasan interesting study into the clipping that can occur evenwhen the digital sample peaks are below the full range af-forded by the system. The authors suggested a measure-ment technique to evaluate this problem and showed resultsfrom a number of processes and commercial devices. Theyfinished by summarizing that the problem could be avoidedby reducing the level either on the recorded media or priorto conversion.

SPEECH PROCESSING AND METADATAThis session started with an invited paper by PatrickBastien of TC-Helicon on voice-specific signal processingtools. He explained some of the unique characteristics ofvoice signals that have to be considered when processingand gave a number of entertaining and informative audiodemonstrations to illustrate the potential pitfalls and solu-tions. He concluded by showing a complex voice-modeling

system that could alter andenhance vocals, but he con-ceded that it could not yetturn Joe Cocker into BritneySpears.

Continuing the topic ofspeech processing, NielsHenrik Pontoppidan andMads Dyrholm of the Tech-nical University of Denmarkcovered the problem of sepa-rating multiple speech signalscaptured with one receiver.Demonstrations of the systemthey developed showed thateven though the resulting au-dio quality was not of a highstandard, the speech signalswere sufficiently separated to

allow further analysis and processing.The final paper of the day was presented on video tape,

because invited author Elizabeth Cohen of UCLA was notable to travel to the conference. In the presentation she dis-cussed the value of metadata and stressed the importance ofcreating metadata at the same time as the content so that itcan accompany the audio signal through the entire chainfrom creation to product.

INTERFACING LOUDSPEAKER AND ROOMOne of the major emerging trends in signal processing forsound reproduction that was discussed at the conferencewas compensation for a less than ideal interaction betweenthe loudspeaker and the room. Saturday morning’s sessionwas devoted entirely to this topic, covering a range frommodal equalization to full room compensation. One of thecommon themes throughout these presentations was the im-portance of the spatial robustness of the processing, to en-sure that any attempts to improve the sound at a single lis-tening position do not degrade the sound anywhere else inthe room.

In the first presentation of the session, Jan AbildgaardPedersen of Bang & Olufsen noted that loudspeaker manu-facturers go to great trouble to optimize a large number ofparameters. However, the final reproduction room of thecustomer has a large effect on the sound. But since the prop-erties of the room can vary widely and are unknown by themanufacturer, they cannot be compensated for in a static de-sign. A solution to this dilemma is the use of active compen-sation, where the processing is adapted to take into accountthe effect of an individual room and even a specific loud-speaker position within that room. Pedersen described onemethod that involves measurement and compensation foreach loudspeaker. He explained that this can be done by in-cluding a microphone in the loudspeaker cabinet to makemeasurements of the loudspeaker radiation resistance fortwo receiver positions. This information can then be used tocorrect the frequency response from 20 to 500 Hz.

A Bang & Olufsen loudspeaker with this technology wasshown in a small demonstration room during the confer-

Clockwise, from bottom left: Wolfgang Klippel, Jean-MarcJot, Ronald Aarts, and Patrick Bastien.

INVITED AUTHORS

AES 23rd INTERNATIONAL CONFERENCE


ence. The loudspeaker was used for replay in more than oneposition in the room, exhibiting the problems of the posi-tion-dependent interaction between the loudspeaker and theroom. The active compensation was then demonstrated byaligning the loudspeaker in each position using the methoddescribed in the presentation. This resulted in the pair ofloudspeakers in different positions having a more similartimbre.

Two further papers on the equalization of room modeswere given by Rhonda Wilson and Michael Capp of Meridian Audio and Matti Karjalainen, Poju Antsalo, andAki Mäkivirta of Helsinki University of Technology andGenelec. The common aim of these papers was to reducethe decay time of low-frequency room modes, though eachused different approaches to analyze and filter the mostprominent modes in a given reproduction room.

The application-based papers on the subject of modalequalization were supported by a theoretical paper presentedby Jean-Dominique Polack of the University of Paris andcoauthored by Jan Abidgaard Pedersen. They used semiclas-sical theory to explain and predict the creation of room

Attendees commented that the quality of the paperspresentations was consistently high throughout the entireconference; questions and comments from the audienceenhanced the exchange of technical information.

Coffee breaks and meals gave attendees time to relax, catchup with old friends, and make new ones.

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modes and the correction requiredfor loudspeakers at different posi-tions. Comparison of measuredand predicted results showed thatthe approximation was reason-able, but that further refinementscould be used to improve the ac-curacy of the predicted results.

Other papers in the sessioncovered a range of topics relatedto the interaction between a loud-speaker and the room. AndrewGoldberg and Aki Mäkivirta ofGenelec presented a paper thatdescribed an automated method to determine thecorrect equalization settings on an active loud-speaker in a given room based on the measured fre-quency response. By the use of heuristic analysisdeveloped from knowledge gained from manualalignment, the complexity of the process was great-ly reduced, meaning that the system could computethe optimum settings in a short time.

A paper by Etienne Corteel of IRCAM andRozenn Nicol of France Telecom focused on theproblems that the reproduction room can cause forwavefield synthesis (WFS) and how the propertiesof the WFS system can be used to compensate forthis. By the use of simulations they showed that


Some of the attendees congregated at the conference center entrance before the short walk to Helsingør Castle.

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Jan Pedersen,right,demonstrates newloudspeakertechnology ofBang & Olufsen.

Wolfgang Klippel, left, demonstrates practical systems for loudspeakermeasurement and active compensation.


WFS can be used to cancel early reflections in the horizon-tal plane over a wide listening area, though only up to thespatial aliasing frequency of the reproduction system.

CREATING SPACE WITH DSPThe Saturday afternoon session focused on using signal pro-cessing to simulate and reproduce spatial properties. An in-vited paper by Jean-Marc Jot and Carlos Avendano of the

Creative Advanced Technology Center considered the prob-lem of combining sources and reproduction systems with awide range of spatial characteristics (mono, 2-channel, and5.1 surround). A number of conversion techniques were dis-cussed, including headphone virtualization, stereo widening,upmixing, and downmixing. To support the presentation aseparate demonstration was given that compared a numberof different techniques for creating a 5-channel surround


Saturday evening attendeeswere treated to a guided tour ofhistoric Kronborg Castle,immortalized by Shakespeare inHamlet.


sound signal from a 2-channel stereo original.The topic of downmixing was continued in a paper by At-

tila Kiss and István Matók of Digital Pro Studio. This ex-plored the use of the center channel when recording in 5-channel surround sound, considering the effect on anypotential downmixing to 2-channel stereo. Yasuyo Yasudaof NTT DoCoMo presented a paper on 3-D audio for mobilecommunications, which highlighted the wide range of waysin which this technology can be applied. The results of anumber of subjective tests that attempted to evaluate theperformance of such systems with varying levels of com-plexity were also discussed.

A paper by Per Rubak and Lars Gottfried Johansen ofAalborg University that considered the perception of col-oration in room impulse responses was presented by PerRubak. This included a detailed literature review on the top-ic, which resulted in the proposal of a new method of mea-suring this effect.

The final paper of the day was presented by JérômeDaniel of France Telecom. He discussed the problem ofcoding distance in spatial recording and reproduction for-mats such as high-order Ambisonics. He explained that Am-bisonics assumes that the virtual sources and reproductionloudspeakers are in the far field, meaning that plane wavesreach the listener. He showed that this is not the case in apractical situation, but that it can be compensated for by us-

ing digital signal processing. Hefinished by suggesting a methodfor simulating the distance of thesound source together with ameans of transmitting the param-eters to ensure that the sound isrendered correctly.

KRONBORG TOUR ANDBANQUETFollowing the final session of theday, the delegates were treated toa tour of Kronborg Slot, a largecastle built in the Dutch Renais-sance style. It is one of thelargest and most extravagant cas-tles of the period. The tourguides explained that the castlewas built to defend the Øresundand to show off the wealth ofDenmark. It is better known inEnglish-speaking countries as theElsinore Castle immortalized inShakespeare’s Hamlet. It is notknown whether Shakespeare evervisited the castle, though he

could have heard descriptions of the castle and the tradition-al Danish tale on which Hamlet is based from the links be-tween the royalty of Denmark and England.

The tour of the castle was followed by a banquet that in-cluded an excellent musical performance by two members ofthe Danish National Symphony Orchestra, Klaus Tönshoff onclarinet and Per Salo on piano. During the banquet RogerFurness, AES executive director, again thanked the organizingcommittee for the hard work that went into making the confer-ence so successful. After the banquet the delegates had coffeein a lounge overlooking the Sound where they viewed a spec-tacular display of lightning, for which Facilities Chair EddyBøgh Brixen would have liked to claim credit, along with therest of the faultless organization.

DSP IN LOUDSPEAKERSThe final day of the conference consisted of two sessions onsignal processing in loudspeaker systems. Ronald Aarts ofPhilips Research Laboratories presented an invited paperwith an overview of a number of digital signal processingtechniques that can improve the end-user experience. Onesuch technique improves the perceived low-frequency per-formance of a loudspeaker by taking advantage of the psy-choacoustic effect of virtual pitch, where a fundamental fre-quency can be perceived even when it is absent. Hesummarized by stating that the combination of DSP and ➥

Subir Pramanik (far left), conferencetreasurer, and Roger Furness, AESexecutive director, welcomed everyoneat Saturday night’s banquet.


psychoacoustics can be a very powerful tool.This was followed by a presentation given by John Mour-

jopolous and Nicholas-Alexander Tatlas of the University ofPatras. They considered the benefits and potential problemsof an all-digital audio signal path from the source to theloudspeaker, including the possible applications of wirelessnetworks and the current limitations in digital loudspeakerdesigns. Peter Mapp of Peter Mapp Associates presented apaper that focused on the range of signal processing em-ployed in sound reinforcement. He outlined the kinds ofproblems that can be alleviated by signal processing andthose that require a physical solution.

Continuing the theme of using digital signal processing tocompensate for poor acoustical performance, two papersdiscussed active compensation of nonlinear distortion inloudspeaker transducers. In an invited paper WolfgangKlippel discussed the need for small, inexpensive, andlightweight loudspeakers with a high power output. Klippelexplained that it can be difficult to achieve high sound qual-ity with such loudspeakers through transducer design alone.He suggested active loudspeaker control as a method of alle-viating some of the problems, and he reviewed the relativeadvantages and disadvantages of a number of techniquesthat could be used for compensation.

Throughout the conference Klippel also gave demonstra-tions of practical systems for loudspeaker measurement andactive compensation. He showed examples of the causes ofnonlinear distortions in loudspeakers and demonstrated theaudible effects on test signals. A short set of measurementswere made of the loudspeaker, from which the required

compensation was derived. The application of this compen-sation to the input signal showed that the problems weregreatly reduced.

Andrew Bright of Nokia also discussed compensation ofnonlinear distortion of loudspeakers in his presentation. Heexplained his use of a simplified algorithm that was ob-tained by a discrete-time model of the loudspeaker nonlin-earity. He also presented experimental results that demon-strated the improvements to be gained by using this model.

The final paper of the conference was by Steen Munk andKennet Skov Andersen of Bang & Olufsen ICEpower. Thisdescribed the use of class D amplifiers, how their perfor-mance may be improved by compensation in the modulatorand in the analog stage of the amplifier, and methods to im-plement control of the amplifier gain. They also comparedthe performance of the class D amplifier with state-of-the-art analog amplifier designs. They found that while the digi-tal amplifier is currently inferior in some respects, it is ex-pected that with further development the performance canbe improved to match or exceed the analog designs.

CONFERENCE CLOSEAfter three days of informative papers that were conduciveto discussion and inspiration, Chair Per Rubak closed theconference by thanking all those involved and hoping thatmany would return for future international conferences inDenmark. Delegates were impressed with the high techni-cal content of the presentations and the relaxed and friendlyatmosphere of the conference. All look forward to similarAES events in the future.


Conference committee: from left, seated, Per Rubak, Ole Moesmann, and Martin Rune Andersen; standing, Subir Pramanik,Eddy Bøgh Brixen, Lars Gottfried Johansen, Knud Bank Christensen, Jan Abildgaard Pedersen, and Crilles Bak Rasmussen.Russell Mason, conference webmaster, missed the photo.

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