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The Science of Sound

By Gregg Sangillo

Mostly white church, with white and gold altar.

Image: Andrea Palladio's Redentore in Venice. Professor Braxton Boren researched the acoustics of Renaissance Venetian churches.

Let's say you're listening to a concert in Washington, DC. Whether it's an indie rock show at 9:30 Club, or a symphony at the Kennedy Center, you probably have an opinion about the sound quality emanating from the stage. But after talking with Braxton Boren, you'll realize just how complicated-and important-acoustics can be.

Boren joined American University's College of Arts and Sciences this semester. As an assistant professor of audio technology in the Department of Performing Arts, he incorporates his background in music theory and composition, physics, engineering, and computer programming. He played a few instruments growing up, but his love of science and math led him to pursue music technology. He recently discussed his work in an edited Q&A with University Communications.

 

UC: How would you describe your research and work?

Boren: It's interdisciplinary connections between music and science, with acoustics being the glue that holds all of my work together. For two years at Princeton as a postdoc, I was working on fundamental technical challenges involving 3-D sound and what we call immersive audio. So, audio systems that take into account how we perceive spatial reality when we're listening to sound in the real world. It's trying to figure out how things sounded in the past, and the role of sound in shaping human history. Taking famous composers and trying to hear how their music would have sounded in its original form.

 

UC: You were awarded a Gates Scholarship to attend University of Cambridge and research the acoustic simulation of Renaissance Venetian churches. Can you talk about that simulation process?

Boren: Two faculty members at Cambridge started a really interesting interdisciplinary project. Malcolm Longair is an astrophysicist, but he's also a very talented musician. His wife, Deborah Howard, is an architectural history professor and specializes in the architectural history of Venice. To probe the connections between architecture and music during the Renaissance, they found that a lot of the music was complex polyphonic music that didn't really fit the acoustics of current spaces. They brought the St. John's College choir from Cambridge to Venice, and even one of the best choirs in Europe couldn't really keep it together in some of these spaces. There was such a long reverberation time that you couldn't hear the rest of the ensemble. They concluded that it wasn't enough to just study the acoustics of the churches as they are now, but you'd have to know more about how these churches sounded in the past. So, they brought me on as a graduate student to build computer models of the spaces, and we calibrated them until they perfectly matched the measurements that were taken in the spaces as they exist today. Then, in consultation with architectural historians, I made changes corresponding to, 'Oh, this altar was taken out. These pews weren't added until later. On the festive occasions, they put in additional seating.' The seating was made of wood, and we figured out what kind of wood it was. And they put tapestries over the walls that would have increased the absorption. And they were completely crowded on the festive days when Claudio Monteverdi music was being performed, and that crowd absorbs a lot of the sound. So, by running simulations, we were able to show that the reverberation time probably would have been cut in half.

 

UC: How much knowledge would a 17th or 18th century European composer have had about the science of sound? Would they have factored in, say, the church's wood or the size of the crowd?

Boren: Were they aware of acoustics the way that we are today? Probably not. Modern architectural acoustics weren't really codified in numerical scientific terms until the very end of the 19th century. But architects had been dealing with sound and designing spaces for hundreds of years, and they knew that certain spaces sounded better when people had designed concert halls. Composers certainly paid a lot of attention to sound in a particular space, and we have documentary evidence of people talking about how they could improve acoustics. Sometimes it was just guesswork, and sometimes they hit on something that's mostly true. Sometimes they're just kind of out in left field. They're probably talking about reverberation times, but they don't have the vocabulary to put it in the modern terms that we would.

 

UC: Even as music technology advances dramatically, many people don't like newer sounds. Some music lovers still prefer vinyl records to digital music. Is there a way to merge the old and the new? For example, if you were streaming songs on Spotify, could you make it sound more like that European concert hall or the pop records from the 1950s and 1960s?

Boren: With the study of concert hall acoustics and church acoustics, and these very large spaces that are very reverberant, we can simulate that really accurately. I record your voice in a small dry environment, so we don't have very much sound reflection in the recording. And then I put your dry audio through this filter, and then that filter adds on every sound reflection that your voice would experience in this space. Then we can hear you with the reverberation time of, say, a big Andrea Palladio church. That is certainly very doable, and it's been used as a research tool. With the question of vinyl, there are some nonlinearities in the audio that are introduced through analog that you don't have in digital. So, often people say that analog has a warmer sound. And there's a little bit of analog compression going on-meaning that not all audio is treated the same at different levels. As you boosted up the higher levels, then all of the dynamic range gets compressed down. So that happens sort of naturally, whereas in digital audio, we apply our own compressor before we put a song on the radio. Modern digital pop audio often sounds a bit more mechanized or artificial, and analog audio, to some people, sounds more alive or vibrant.

There's also this affiliation of putting yourself out there as a person who likes analog. That's just people wanting to be different, or just to show that their taste is superior to other people. If you made a digital filter that completely reproduced everything about an analog, vinyl record, those people would still not be satisfied, I think, because that takes away their reason for wanting to listen to records in the first place.

 

UC: Can you discuss how your work with music relates to virtual reality?

Boren: I think virtual reality is a powerful tool for how we understand music in its original form. If you hear a song on the radio when you're 17 and driving in your car, and then you hear it 30 years later, it brings you back to that moment. It's not just the audio that you were hearing. It was actually a place, a time, a whole scenario that you were experiencing. If you listen to a song from the 1960s today, and you weren't alive in the 1960s, you're not really going to understand the full context of that song. If you've never listened to something in a car stereo, you might not understand the audio that was mixed and compressed to be heard over a lot of road noise in a car. The music that we teach gets vastly reinterpreted to sound quite a bit different than it would have in its original environment. So, I see virtual reality as another step toward accurately rendering what it was like to be a person interacting with this music at any point in time. That could have been 20 years ago, or it could have been 400 years ago.

When we think about history, it tends to seem very stodgy and stuffy. But if you can go back and listen to it, or experience it, or put yourself in the same seat with somebody listening to this music for the first time, then we can start to understand. Today, if you go to a classical music concert, it's for the wealthy elites. Those are the only people keeping classical music alive now. And there's this sort of unspoken code of how you're supposed to behave. You shouldn't unwrap any candies, you shouldn't clap between movements. If you get excited, and you happen to clap because something really moved you, then everyone is going to shame you into silence. But if you read historical accounts, this was the popular music of its time. People were really excited, and people would routinely cheer. It was sort of the punk rock concert of its time, and it had a completely different energy. Until you understand that, it's going to be difficult for our students to enjoy this music in a way that's real and vibrant today.