ISRA2013

Toronto, Canada International Symposium on Room Acoustics

2013 June 9-11

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Recreation of the acoustics of Hagia Sophia in Stanford’s

Bing Concert Hall for the concert performance and recording of Cappella Romana

Jonathan S. Abel1, Wieslaw Woszczyk2, Doyuen Ko2, Scott Levine2, Jonathan Hong2, Travis Skare1, Michael J. Wilson1, Sean Coffin1, Fernando Lopez-Lezcano1 1Center for Computer Research in Music and Acoustics (CCRMA) Department of Music, Stanford University, Stanford, CA 94305 USA 2Centre for Interdisciplinary Research in Music Media and Technology (CIRMMT) Schulich School of Music, McGill University, Montreal, QC, Canada

ABSTRACT

Bing Concert Hall designed by Nagata Acoustics was inaugurated in January 2013 at Stanford University. The hall’s 842 seats are arranged in a “vineyard” format with the audience surrounding the performers. The February 1st concert performance of the renowned American vocal chamber ensemble Cappella Romana entitled “From Constantinople to California” was staged in Bing Concert Hall with the recreated acoustics of the magnificent Byzantine architecture of Hagia Sophia in Istanbul rendered by 24 loudspeakers. In the preparation for this event, rehearsals were conducted within a small space at CCRMA and simulating the acoustics of Hagia Sophia using 16 loudspeakers. The concerts and rehearsals were recorded in surround sound and using close microphones. The acoustics of Hagia Sophia was measured using recordings of four balloon pops, which served as a basis for the creation of multiple impulse responses used in low-latency recreation of the acoustics by employing multichannel convolution. Spatial rendering resulted in a fully immersive interactive experience for the singers and their audience. The paper describes the implementation of active acoustics needed to accommodate the performance of Byzantine liturgical chant for Hagia Sophia.

1 INTRODUCTION

This work describes the result of an experiment with digital technology to transform the Bing Concert Hall into the reverberant soundscape of Hagia Sophia, Istanbul. This experiment was part of the "Icons of Sound" project, http://iconsofsound.stanford.edu, which explores the interior of Hagia Sophia through visual, textual and musicological research, video, balloon pops, architectural and acoustic models, auralizations and the performance and recording of Byzantine chant. Previous Icons of Sound acoustics and auralization work includes processing balloon pops recorded in Hagia Sophia into impulse responses of the space1-2, and producing auralizations of Byzantine chant in a virtual Hagia Sophia3. The auralizations were accomplished by recording chant performed using headset microphones, so as to have separate dry tracks for each of the performer's vocals. While chanting, the microphone signals were processed using the

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estimated Hagia Sophia impulse responses, and played for the chanters over headphones to provide in real time a virtual sense of the performance space, while allowing dry vocal signals to be recorded. In post-production, the recorded dry tracks were processed according to the estimated Hagia Sophia impulse responses to produce performance recordings in a simulated Hagia Sophia. In the following, we describe the live performance of Byzantine chant in a virtual Hagia Sophia, created in Bing Concert Hall, Stanford University, during a concert by Cappella Romana on February 1, 2013. Such a live auralization is made difficult by the extremely wet, reverberant acoustics of Hagia Sophia, which can easily produce feedback between the singer microphones and hall speakers. For the performance, we used Countryman B2D hypercardoid microphones affixed to the singer's foreheads and pointed downward, in combination with an array of 24 full range loudspeakers and six subwoofers, strategically placed throughout the hall above the performers and audience. A total of 48 statistically independent impulse responses, corrected for the existing acoustics of Bing Concert Hall were used to simulate the enveloping sound field of Hagia Sophia. This paper is organized as follows. We describe the hardware and signal processing used to simulate the acoustics of Hagia Sophia in Stanford's CCRMA Stage for rehearsal and recording in Section 2, and for live performance in Bing Concert Hall in Section 3. An evaluation of the results appears in Section 4, and conclusions in Section 5. We first describe the acoustics of Hagia Sophia and Bing Concert Hall, and review aspects of virtual acoustic performance and technology.

1.1 Acoustics Aspects of Hagia Sophia and of Bing Concert Hall

Opened on December 27 in 537 AD, Hagia Sophia in Istanbul, Turkey (sometimes referred to as the Great Church of Constantinople) is a former Basilica of the Christian Orthodox Church and a monumental example of Byzantine architecture. The complex structure with colored marble walls has a large central dome 31.87 m in diameter, supported by four main arches and a number of semi- domes. The church is 82 m long, 73 m wide, and 56.60 m high, has the volume of 255,800 cubic meters, with 67 columns in the upper gallery. The reverberation time of Hagia Sophia is nearly 11 seconds, which lends unique properties to the music and demands suitable repertoire and singing ability. The curved mosaic dome surfaces and large, open naive, bounded by marble colonnades, efficiently sustain acoustic energy and create an acoustic waterfall effect that varies in intensity depending on the location of observation or measurement. Since 1935, Hagia Sophia is a museum of the Republic of Turkey and is open to the public, but since no concerts or liturgical music performances are permitted, there is no possibility to hear Hagia Sophia as a venue for music. As noted by Bissera Pentcheva4, in a sense, Hagia Sophia has lost its voice. Figure 1 shows two views of the Hagia Sophia Museum interior.

Bing Concert Hall5 was inaugurated on January 11, 2013 at Stanford University. Designed by Richard Olcott of Ennead Architects with acoustics by Yasushita Toyota of Nagata Acoustics, the hall accommodates 842 seats surrounding the stage, in a vineyard terrace format. Concrete enclosure 0.3m in thickness isolates the interior from external sounds. The curved canopy reflector located above the stage at the height of 48 ft provides sophisticated rigging, lighting and sound support, and convex-shaped sail-like reflecting walls diffuse and absorb sound in a critical manner. Absorbing curtains provide additional control of reverberation, which is roughly 2.5s T30 with all of the curtains deployed. These two contrasting spaces were linked acoustically on February 1st, 2013 to enable the performance of Byzantine chant, recreating parts of liturgical service of the Christian Orthodox

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Church from the 12th through 15th centuries.

Figure 1: Two photographs of the interiors of Hagia Sophia Museum in Istanbul.

Figure 2: Large central dome 31.87 m in diameter, supported by four main arches and a

number of semi-domes within Hagia Sophia Museum in Istanbul.

1.2 Acoustic Requirements of Cappella Romana and of Byzantine Chant

The historical evidence suggests that the compelling acoustics of Hagia Sophia with its long reverberation time, diffuse early reflections and isolation from external noise has affected the composers and the performing style of vocal ensembles in service of liturgy. Simple harmonies, sustained drones of low notes, and high-pitched textures could bring out the shine and angelic beauty of the acoustics in the service of music, liturgy, and emotion. The sound of Hagia Sophia

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was treated as the inseparable component of the music; it was uplifting, lending power and solemnity to the words and harmonies, enriching the ceremony and prayer6. Cappella Romana7, the renowned American vocal chamber ensemble specializing in Byzantine Chant would have the opportunity to experience singing the Kontakion, Trisagion, Prokeimenon and the Cherubic Hymn in the splendid acoustics of Hagia Sophia, recreated in Stanford’s Bing Concert Hall with the aid of digital signal processing based on acoustic measurements made in the Hagia Sophia Museum in Istanbul. The original manuscript scores were edited for modern performance by Ioannis Arvanitis9. The long reverberation allowed for a simple monadic chant to become a beautiful tapestry of chords created by overlapping transitions between the voices. The responsorial manner of chanting the psalms, when at times one group sings a line while the other sustains a drone, also allowed for beautiful interactions of singers with the reverberation of the enclosure, creating complex mixes of melodies, harmonies, and rhythms. This musical and sonic outcome was only possible with the acoustical treatment interactively imposed by Hagia Sophia.

1.3 Music Performance in Virtual Acoustics

Musical performance in virtual acoustics is an attractive solution to achieving proper acoustical conditions for musical performance in venues having natural acoustics that are more dry than that demanded by the music---that is acoustic conditions which were not intended for the music as written or for the requirements of performance. For example, music written for a chamber being performed in a 3000-seat space, or music written for an orchestra performed in a rehearsal room. Several examples of implementations of virtual acoustics exist where active acoustics mimics the necessary presence of room acoustics to complement musical performance. In particular, outdoor spaces are good candidates for using such approach. The acoustics of Tanglewood’s Seiji Ozawa Hall10 is typically extended to include the expansive lawn behind the concert hall by using a surround sound system outdoors reproducing the ambience of the interior performance. In this case, outdoor listeners being outside the acoustics of the performance space are enjoying sound having the appropriate concert hall acoustics. Another approach is to use hundreds of speakers and microphones to generate reverberation having the desired characteristics. In Chicago, at The Jay Pritzker Pavillion in Millennium Park, there is a LARES installation allowing 12,000 patrons to share the experience of a virtual acoustic enclosure11-12. Meyer Sound Constellation with VRAS reverberator provides changeable acoustical conditions in the installation outside of the New World Symphony hall, allowing the outdoor audience the experience of a virtual hall13. At McGill University, Virtual Acoustics Technology (VAT) has been developed to create virtual acoustic environments to enrich musical performances based on low-latency multichannel convolution of carefully measured impulse responses from some of the most renowned acoustic enclosures in the world14-16. This system uses only 16 dodecahedron speakers and eight microphones, but locates them strategically about a hall with a relatively short reverberation time. The technology serves to research interactions between musical performance and acoustics17-19. A number of public concerts have been organized by CIRMMT20 using VAT and a complete set of surround and stereo recordings made in virtual acoustics have been issued by NAXOS21 to critical international acclaim22-23. Previous studies of the acoustics of Hagia Sophia include the work of Christoffer Weitze, Anders Christian Gade and Jens Rindel with their Danish colleagues at Odeon (Denmark)24-26 who measured impulse responses in Hagia Sophia using 3 sources and 11 receiver

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positions. These measurements were used to verify that their Odean software produced impulse responses with similar characteristics, T30's, C80's and the like. Once the model was constructed, the software could be used to generate a practically unlimited number of impulse responses based on the location of assumed sources and receivers. For auralization, the Danish group convolved off-line a recording of Byzantine chant with these synthesized impulse responses of Hagia Sophia. In contrast, this project creates many estimated impulse responses by deriving them from a single balloon pop recorded in Hagia Sophia in 2010. The technique described by Abel1-2 allows for efficient generation a large number of statistically independent impulse responses based on the echo density profile and amplitude envelope model of the reference response. The convolution is performed in real time allowing immediate auralization of live performance in the recreated acoustics of Hagia Sophia.

2 IMPLEMENTATION OF VIRTUAL ACOUSTICS OF HAGIA SOPHIA IN CCRMA’S STAGE FOR THE REHEARSALS AND RECORDING

Prior to the performance in a public concert, a series of rehearsals were held privately in the small concert space called Stage, at the Centre for Computer Research in Music and Acoustics (CCRMA) at Stanford University. The goal was to immerse the singers of Cappella Romana in the intense reverberation of Hagia Sophia and to allow them to work on the interpretation of their Byzantine chant concert repertoire. The vocal ensemble was eager to work on specific vocal balances and articulations strongly affected by the acoustics, and requiring various adjustments. It was also necessary to arrange a real-time auralization of Hagia Sophia to test the susceptibility to feedback and the quality of virtual acoustic environment.

2.1 Layout of Loudspeakers and Performers

The singers were arranged in a circle around the center of Stage, allowing them to be facing each other for greater audibility and easy gestural communication between them and the conductor. The performers were seated behind their music stands, and were surrounded by 16 full range loudspeakers and eight subwoofers manufactured by Adam. There were 8 loudspeakers overhead, suspended from the ceiling rigging system, and 8 loudspeakers in the horizontal plane on stands. Figure 3 shows the layout of singers and loudspeakers in the CCRMA Stage, and the application of the lavalier microphone on Alexander Lingas’ forehead.

Figure 3: The layout of singers and loudspeakers in the CCRMA Stage, and the application of the lavalier microphone on Alexander Lingas’ forehead.

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2.2 Preparation and Rendering of Impulse Responses

Impulse responses of Hagia Sophia were derived recordings of balloon pops in the museum by Bissera Pentcheva1. The process1 involves estimating the echo density and frequency band energies estimated in running windows over the balloon pop response, and then synthesizing a pattern of full bandwidth echoes matching the measured echo density profile, and imprinting the measured band energy profiles. By generating statistically independent echo patterns, multiple mutually decorrelated impulse responses can be created mimicking the reference response of the balloon pop. Such impulse responses can be used in auralization via low-latency convolutions once their dynamic range is sufficiently extended beyond that present in the recorded balloon pop2. Figure 4 shows the impulse response and spectrum of the balloon pop recorded in Hagia Sophia along with an example restored estimated impulse response.

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Figure 4: The impulse response and spectra of the balloon pop recorded in Hagia Sophia - on the left, and the restored estimated response - on the right. Time is presented in logarithmic

scale for clarity. The major peak of reflected energy corresponds to the dome reflection.

Figure 5 shows the improvements attained in the quality of impulse responses captured in Hagia Sophia and used in recreation of the acoustics of Hagia Sophia.

Figure 5: Spectrograms of the balloon pop response contaminated with speaking voices (left), non-contaminated response (center), restored and synthesized impulse response (right).

Reverberation time in linear scale. Impulse responses based on Hagia Sophia.

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In rehearsals and recording sessions conducted on CCRMA’s Stage, sixteen statistically independent impulse responses were used in sixteen instances of monophonic convolution using Altiverb 6 plugin in a Protools session. Each of the 16 independent convolutions was feeding one of the 16 loudspeakers. Listening to reverberation in between any set of loudspeakers, one was aware of a broad image of diffused reverberation. Since Hagia Sophia features predominantly the late reverberation and little, if any, of early reflections, the rendering in the listening room was thought to approximate the museum acoustics. Countryman Associates Model B2D Directional Lavalier microphones were mounted on the upper forehead of each of the 15 singers using a medical tape resistant to sweat, and were wired to Yamaha DMC1000 console for preamplification and distribution to loudspeakers. A laptop computer was running Protools session inserted within the Yamaha mixer and including the convolutions. The computer was also used to record the 15 microphones signals from individual singers, as well as a stereo pair of crossed-figure-8 microphones arranged in the middle of the circle to capture the acoustic balance of all performers in the virtual acoustics of Hagia Sophia. The recording of lavalier microphones was serving dual purpose, to inform about the amount of leakage from recreated reverberation and from other singers, and to provide a “dry” acoustic recording of each voice for post-production and subsequent investigations. There was also a second pair of microphones in center that was used to feed the convolution reverberator when the lavalier microphones were not available. It turned out that it was possible to achieve substantial amount of Hagia Sophia acoustics without feedback using just these two room microphones. We attribute this to the highly decorrelated statistically independent late reverberation produced by each of the sixteen loudspeakers, somehow able to “diffuse” the room modes in the Stage.

2.3 Sound Balancing for Rehearsing and Recording

Sound balancing in the room avoided feedback by pointing the lavalier microphones down towards the singers’ mouths while boosting the sound from loudspeakers located overhead that was more audible and not easily baffled by musicians. In one approach, only the lavalier microphones were used for convolution, their outputs adjusted to create a mono mix feeding all 16 convolution engines. The balancing adjustments were performed after the microphones were mounted on singers’ foreheads and each one would sing a passage to allow setting of the balance and equalization complementing the microphone placement. Since each singer contributed to all convolution outputs via the common send buss, the balance was from then on controlled by the singers with only a small adjustment made by mixing engineer between the gain of overhead speakers and horizontal speakers, and the overall loudness of reverberation. Only the intended musicians were able to stimulate the reverberation of Hagia Sophia, not anyone else present or talking in the room. This is the first time at CCRMA when loudspeakers were used to generate virtual acoustics for live performance and the outcome was impressively providing high level of Hagia Sophia reverberation without feedback. In the earlier tests at CCRMA, reverberation was provided to performers via headphones but it was isolating them from each other, only providing a guide for timing of performance. This time they were truly hearing each other and singing with each other immersed in the acoustic space created by using the loudspeakers.

In a second procedure, only a stereo pair of crossed-figure-8 microphones (Sennheiser MKH 800) was used to feed the 16 convolutions, without any individual lavalier microphones. The outcome was somewhat more prone to coloration and possibly feedback but still allowed to achieve a strong sense of immersion in the acoustics of Hagia Sophia. In this case, all persons present in the room could trigger the reverberation of that space, not just the singers.

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3 IMPLEMENTATION OF VIRTUAL ACOUSTICS OF HAGIA SOPHIA IN BING CONCERT HALL FOR THE PUBLIC CONCERT PERFORMANCE AND RECORDING

The February 1st public performance in Bing Concert Hall was to transport Cappella Romana and sold out audience into the historic space of Hagia Sophia to experience the Byzantine chant, including versions of the Kontakion, Trisagion, Prokeimenon and the Cherubic Hymn from the 12th through 15th centuries.

3.1 Layout of Loudspeakers and Performers

The goal of the speaker layout was to provide as much as possible an even distribution of the generated sound of Hagia Sophia over the span of the audience. This proved to be quite difficult in the vineyard-terrace type architecture because the loudspeakers could not be suspended close to the seats without obstructing the visual field of patrons sitting above. The hall has a terraced design with the audience seated at different levels and surrounding the stage. Consequently, the loudspeakers were placed considerably further away from the audience members sitting in the center of the hall, than those located at the edges of the hall. Figure 6 shows the locations of the loudspeakers suspended overhead and mounted on stands (left), and the locations of singers in the center of the stage during the dress rehearsal (right). Altogether, 24 QSC HPR122i main speakers and 6 QSC HPR181 subwoofers were used to project Hagia Sophia acoustics into Bing Concert Hall. Ten main speakers were arranged around the upper terrace, which included two front speakers on stands, four speakers on each side of the Hall in the lower catwalks, and four more speakers in the sides and back, also on stands. The speakers rigged from the ceiling were arranged in two “rings”, a medium height ring comprised of 10 speakers and a high ring of 4 speakers. The placement of the speakers was dictated by the spacing and availability of rigging points therefore exact symmetry of the arrangement could not be achieved.

Figure 6: The locations of the loudspeakers suspended overhead and mounted on stands (left),

and the locations of singers in the center of the stage in Stanford’s Bing Concert Hall (right).

The real-time projection of the Hagia Sophia acoustics in Bing Concert Hall had to reach sufficient loudness to invoke strong sensory awareness of this space above that of Bing Hall. Considering the extremely reverberant acoustics of Hagia Sophia, there was a danger of feedback between the singer microphones and hall loudspeakers due to high amplification needed to boost the reverberation. To reduce the chance of feedback, individual Countryman Model B2D hypercardoid microphones were affixed to each singer's foreheads and pointed downward. Microphone signals were sent by Shure transmitters and received by antennas in

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the Hall, which were connected to wireless receivers each located in the technical room to the side of the hall. From there they were routed the hall's main Yamaha SL5 mixer, which was used for level control and signal equalization. The 16 signals were then sent out of a dual ADAT link card into an audio workstation for mixing, processing, and projection into the hall. The speaker rigging maps, for both floor-mounted and suspended units, are presented in Figure 7.

Figure 7: The plan view of the locations of the horizontal loudspeakers mounted on stands (left), and the suspended ones overhead (right), in Stanford’s Bing Concert Hall (right).

3.2 Rendering System and Spatialization of Recreated Acoustics

A Linux based workstation having a 6 core, 12 thread i7-3930K processor, with 64G of RAM, and an SSD system disk with two disk mirrored RAID array was used for convolution and for ambisonic spatialization processing that generated and distributed audio signals of Hagia Sophia reverberation into the concert hall via the 24 full range loudspeakers and six subwoofers. The workstation and Yamaha mixer were set up in the main mixing position at the back of the hall, from there signals were connected through ethernet to the amp/patch room and via D/A converters to the loudspeakers. A total of 48 statistically independent impulse responses, each 12 seconds long at 48kHz sampling frequency, were used to simulate the enveloping soundfield of Hagia Sophia. They implemented a fully spatialized auralization based on the estimated Hagia Sophia impulse responses, and corrected for the existing acoustics of Bing Concert Hall. The convolutions were performed by four instances of jconvolver processing27 done within the Ardour2 session28. All 48 returns of reverberation plus direct microphone signals were distributed into the loudspeakers via ambisonic decoder plugin designed for this particular speaker-based diffusion by Aaron Heller and Eric Benjamin29. Technical details of the system design can be found in a related paper30. Only the lavalier microphones were used for generating the reverberation of Hagia Sophia through convolution. The three stereophonic microphone pairs hanging over the stage, the front and the mid part of the audience, and the stereo pair on the stage, were only used for recording of the live concert. No loudspeaker feeds were recorded.

For the performance, the Cappella Romana vocal ensemble utilized 12 melodists and 3 bass drones, with the melodists forming a circle and the drones placed behind the group. According to historical records, in Hagia Sophia the choir would be arranged in a circular configuration on

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the ambo (a raised stand in early Christian churches from which parts of the service were chanted or read). To effectively spatialize the performance, each of the 12 melodists’ microphone signals was convolved with 4 Bing-corrected Hagia Sophia impulse responses and distributed using ambisonics to create clusters of localized diffuse reverberation. These overlapping zones of reverberation were arranged artistically about the hall so that different listeners in different places around the hall would have a sense of varying spatial depth in the reverberant sound field. The three bass drone microphone signals were each mixed with four melodist signals and therefore each drone appeared in 16 of the convolutions and all zones of reverberation. The goal was to have the bass widely distributed and permeating the acoustic space of Bing Hall as the essential musical foundation set for the melodic lines that were more spatially articulated.

3.3 Audience Effect on Composite Acoustics

The impulse responses used in the concert had to be preprocessed by accounting for the reverberation contribution that was estimated to come from Bing Concert Hall. Such processing was not needed for the Stage, as it has a 0.5s T30.

During the performance in Big Concert Hall, audience members would hear three types of sound arrivals in different proportions depending on where they were seated: 1) direct sound from performers, 2) indirect sound of performers imprinted with the acoustics of Bing Hall; 3) sound from the loudspeakers reproducing indirect sound of voices convolved with Hagia Sophia impulse responses. The goal was to create the correct balance of these sound field components in order to produce the same psychoacoustic impression as would be heard by a performer or listener in Hagia Sophia. To achieve this we processed the Hagia Sophia’s responses to account for the Bing acoustics such that the acoustic energy envelope as a function of frequency that the listener experienced in the concert hall would match that of the Hagia Sophia response estimated from the measurements. Considering the different relative decay rates of Hagia Sophia and Bing Hall late field responses, we see that in the beginning of these impulse responses, there is little difference in energy between the 2.5s long response of Bing and the 11s long response of Hagia Sophia. But as time progresses through the decay of the IRs, the Hagia Sophia response becomes dominant in energy, increasingly louder than Bing. Accordingly, the “corrected” IR begins impulsively (to kick off the Bing Hall response) and cross-fades into the Hagia Sophia response (to provide the Hagia Sophia energy envelope after the Bing response has decayed).

While the audience effect of absorption was not measured, we were aware of the possibility of reduced audibility of the ambient sound in the presence of the audience, and ready to counteract with increased gain of both, the amplification of direct sound and of convolution reverberation. The comparison of two surround 5.1 recordings made with six suspended hall microphones during dress rehearsal and concert shows that there was little difference in the level of ambience between the two. The minute compensation of gain during the performance was able to recreate similar intensity of ambience during the sold out concert.

4 EVALUATION OF RESULTS AND RECOMMENDATIONS

The two cases of recreated acoustics of Hagia Sophia for live performance in two venues of different size and acoustics, using two types of technology based on convolutions, show that it is possible to build a convincing acoustical environment for interactive performance. It is essential that the musicians are given full control of the balancing of their acoustic contribution with the acoustic response of the virtual enclosure. The acoustics cannot be a moving target for a musician but a reliable component of his/her instrument. This is particularly true of vocal

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performers who have the intimate control of sound projection and the ability to assess that projection by careful monitoring of the ambient acoustic response. The key requirement for interactive acoustic performance in synthesized acoustics is low latency, since the delay not only changes the size impression of the venue but also of the timing and articulation required in performance. In the case of Hagia Sophia, there was a relaxed latency requirement because the impulse responses had delayed early reflections do to the size of the museum, and the dominant acoustic component was at the tail end of impulse response. Therefore, it was impossible to test the sensitivity of the singers to threshold values of latency with these signals. Any latency contributed positively to the already large sensation of the space. The goal of generating statistically independent impulse responses and using a large number of them (16 in rehearsals and 48 in concert) proved to provide a strong immunity from feedback and sound colorations. Each loudspeaker produced an independent response from other loudspeakers. While estimated impulse responses derived from a model can provide very useful results, it is not clear whether the same technique can generate representative impulse responses for smaller venues rich in early reflections. The benefit of ambisonic control of panning and sound distribution is also not clear as there was not enough time to study this topic systematically in the actual concert venue. The application of lavalier microphones placed closely to the sound sources was clearly very beneficial in terms of low colorations and lack of feedback. It allowed each singer to have direct control of reverberant balance and contributed well to the sense of the ensemble in performance.

5 CONCLUSIONS

The acoustic enclosure can have a dramatic impact on musical performance and on the perception of unity in score, interpretation, and historical validity. The impact of acoustics in music performance should be studied in depth as this may generate new knowledge about aspects of room acoustics required in creating new designs of concert and performance venues. The experience of recreating the acoustics of Hagia Sophia has shown that room acoustics is an indispensable, integral component of the musical instrument a performer tries to control in the act of performance. The room, whether real or virtual, is an essential channel of communication in music and helps to evoke deep emotional bond between the artist, the music, and the listener. This was plainly evident in the virtual acoustic performances of Cappella Romana of ancient music that was composed for Hagia Sophia. The music and acoustics blended so thoroughly that listeners and performers in the post concert recording sessions felt overwhelmed by the power of the experience. It seems possible, using virtual acoustics, to bring musical performance to a higher level of emotion and to study these aspects further using such tools.

ACKNOWLEDGMENTS

This research was enabled by the Stanford Presidential Fund for Innovation in the Humanities, granted for “Icons of Sound: Architectural Psychoacoustics in Byzantium”, the Stanford Institute for Creativity and the Arts (SiCa), and the generous support of Christine and Reece Duca, with additional support provided by the Center for Computer Research in Music and Acoustics (CCRMA). We also gratefully acknowledge the support of Natural Sciences and Engineering Research Council and of Social Sciences and Humanities Research Council of Canada, and of

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Hagia Sophia Museum and The Turkish Ministry of Culture and Tourism. Special thanks go to Chris Countryman for lending us the lavalier microphones.

REFERENCES

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24 Christoffer A. Weitze, Claus Lynge Christensen, Jens Holger Rindel and Anders Christian Gade. Computer Simulations of the Acoustics of Mosques and Byzantine Churches. 17th ICA, Rome, Italy, September 2 – 7, 2001.

25 Weitze et al., “The Acoustical History of Hagia Sophia revived through Computer Simulations”. http://www.dat.dtu.dk/cahrisma.htm;www.odeon.dk/pdf/ForumAcousticum2002.pdf

26 http://www.odeon.dk/acoustics-ancient-church-hagia-sofia 27 Jconvolver http://kokkinizita.linuxaudio.org/linuxaudio/ 28 Ardour2 http://ardour.org 29 Aaron Heller, Eric Benjamin, Richard Lee, “A Toolkit for the Design of Ambisonic Decoders”, Proceedings of LAC2012. 30 Fernando Lopez-Lezcano, Travis Skare, Michael J. Wilson, Jonathan S. Abel, “Byzantium in Bing: Live Virtual Acoustics Employing Free Software”, Manuscript submitted to Linux Conference 2013.