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Thursday, July 30, 2015

The sound of music, according to physicists

"Researchers elevate musicians in the air and attach lasers to their instruments." reports Brigham Young University (BYU).

The musicians played in an echoless room with lasers helping them hold the instruments perfectly in place. Photo: Brigham Young University (BYU)

Joshua Bodon is sick of hearing "Somewhere Over the Rainbow." More specifically, he's sick of hearing one 25-second clip of the song repeated more than 550 times.

For almost two years, this physics grad student has been testing how sound radiates from live musical instruments, which includes hearing the same song over and over… and over. But the monotony has a purpose; it's all about helping musicians, instrument makers, concert hall designers, audio engineers and music producers enhance sound quality.

The work takes place in one of two anechoic chambers at BYU. Anechoic, meaning "free from echoes and reverberation," describes a room built with walls that absorb sound energy, so noise can't bounce back to a listener.

Bodon and physics professor Timothy Leishman devised a recording system with a rotating chair and a semicircular array of 37 microphones that puts musicians out of their comfort zone.

"Some people go in there and it's so quiet that it feels like everything is imploding in on them," said Darin Bradford, a music professor who played several instruments for the research. "I was really happy to be involved – it was a really fascinating experience."

The musicians who play for the study face three difficulties that they never encounter in a concert hall:
  • They have to sit on a chair elevated several feet above the floor. That allows the research team to capture sound that radiates downward.
  • The walls don't bounce sound back to the musician, which changes how they hear the notes they play. If any note in a chromatic scale or musical excerpt is slightly off-key, they've got to start over.
  • While they play, they have to keep a laser that's attached to their instrument pointed inside of a target. Slight movements that move the laser outside of the target alter the direction of the sound waves.
When they finally get everything right, the chair rotates five degrees, and they do it all over again. The process repeats 72 times until the 360-degree revolution has been completed. A complete recording for one instrument can take anywhere from five to eight hours. Fortunately these musicians – both students and faculty at BYU - get paid. They also get a break each time they have rotated 90 degrees.

When the recordings are finished, Bodon and his team of three undergraduates, Michael Dennison, Claire McKellar and Michael Rose sort through the data – about 250 gigabytes per instrument. The students create balloon plots that map each instrument's sound radiation over a sphere. The team has become so proficient at this process, that they can do it start to finish in less than 24 hours.

So far the team has completed recordings and mapping of the cello, violin, trombone, French horn, baritone saxophone, oboe, clarinet, bassoon, viola and trumpet.

Source: Brigham Young University (BYU)

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