MIT guitar combines acoustics and electronics

Acoustic instruments with their wood-grain patterns produce unique sounds, but a prototype guitar built by a Massachusetts Institute of Technology student combines the natural acoustics of wood with the power of electronic processing.

Called the Chameleon Guitar, it can mimic different instruments using an on-board computer and replaceable wood soundboards.

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Instead of having a full-shaped chamber, like an acoustic guitar, violin, or other string instrument, the Chameleon's wood soundboard has several small sensors that send acoustic information to a computer that then interprets and processes the sounds. "So what we have is the authentic behavior of the wood, but we also have the computer control like a synthesizer, but it's much more authentic than a synthesizer," said Amit Zoran, the developer of the guitar and a student at MIT's Media Lab.

"A normal synthesizer synthesizes the fundamentals of a sound and is something created on a computer, but here we don't create the sound from nothing," Zoran said. The strings vibrate and attenuate the bridge of the guitar and then the sound moves like any other acoustic instrument.

Wook Yeon Hwang, a guitarist for 20 years and MIT Media Lab associate agreed. "The problem with synthesized instruments is that they pick a sound at one particular moment so every time it sounds the same," he said. "It's almost impossible to put my feelings into the music."

Being able to play on a guitar that uses the natural acoustics of the wood, instead of synthesis, is much better and much more important to musicians, said Hwang, who gave Zoran feedback as the guitar was developed.

Zoran only has two working wood soundboards for now. Both are made from red cedar, but one creates a sound that is more like an acoustic guitar, sonorous and open, while the other mimics a hard-body instrument and the sound of an electric guitar. The soundboards can be replaced in about 15 seconds, with the guitar needing to be retuned each time. At the tapered end of the board, opposite the bridge, there is a chip that plugs into the on-board computer and relays sound signals gathered from each pluck of the instrument.

Zoran has fabricated other experimental soundboards. One has metal screws in it and Zoran said that when the screw placement is changed, the sound will as well. One soundboard is hollow with a rubber stopper, allowing it to be filled with water or oil, which will create different acoustic properties. Yet another soundboard is made from the wood of a 150-year-old bridge in Vermont. Making an entire guitar from the aged wood would be near impossible if not prohibitively expensive, but because the soundboard is small the project was manageable.

At the heart of the instrument, and the part that has yet to be fully developed, is an on-board processing computer. On the front of each of the soundboards are five electronic pick ups that feed two stereo signals and one mono signal into the processing chip. Using software, the computer will interpret the unique sounds from the wood soundboard, mix it with the electronic audio properties on the chip and output the sound to an amplification unit.

Since the current prototype doesn't have the on-board software, Zoran said that what is being heard is only 5 percent of the actual sound that can be produced by the guitar -- only the natural resonation of the each of the unique wood soundboards can be heard. Once the software is written, Zoran said that musicians will be able to experiment in ways never possible, such as "playing" a guitar that is the size of a skyscraper.

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Under the direction of MIT Media Lab Associate Professor Pattie Maes, Zoran has been working on the Chameleon Guitar for about a year. He finished his proof-of-concept in August 2008 and after receiving positive feedback from Hwang and other musicians, he decided to take it further. Zoran worked with a Boston instrument maker, Marco Coppiardi, to build the guitar from scratch. Zoran's next step is to further integrate the guitar's computer and program the software. After that, he'll continue testing it with professional players, refine it and hopefully bring it to market.

Zoran wants to be able to give musicians something that they can't get from an acoustic instrument -- the freedom to change the sound.

"That is something that exists on synthesizers and digital instruments, but they lack the authentic properties of wood." Zoran thinks his creation will open up experimentation for musicians because they will no longer need to purchase multiple, expensive instruments.