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On the path to a virtual violin, musician creates the vBow

In the never-ending rhapsody of musical innovation, the vBow sounds a small but significant note.

Invented by Charles Nichols, a doctoral candidate in computer music theory and acoustics, the virtual violin bow resembles its traditional counterpart only in passing. A fiberglass rod moves back and forth through a hole at the end of a robotic arm, which is connected to an acrylic base shaped like a violin.

Yet this contraption, which uses servomotors and encoder sensors instead of strings, acts and sounds like a real violin bow does on real violin strings. By all accounts, Nichols, 34, is the first person to have developed a virtual stringed instrument that employs haptic feedback, allowing the musician to actually feel as though he is playing a violin.

The vBow also is Nichols' first step toward developing a computer-music instrument he can play as violinist. Once completed, the virtual violin, or vViolin, will allow him to produce computer music that is more expressive than that of a MIDI (musical instrument digital interface) violin. The vViolin also will allow Nichols to produce a vast range of sounds -- such as those of a trumpet or double bass, to cite two conservative examples -- but by using violin motions and technique.

"This work came out of my work as a violinist and composer trying to write interactive computer music that was expressive for a performer and rich in timbral and dynamic contrast," Nichols explained the other day, sitting in a trailer office behind the Center for Computer Research in Music and Acoustics. On the wall behind him hung a series of vBow bases staggered from left to right -- from earliest to more recent -- like a depiction of evolutionary man.

"I decided to develop an instrument I could play as a violinist," he added. "I don't have to play a keyboard, and I don't have to play a wind controller, and I don't have to try to get MIDI to sense what I'm doing."

Nichols, who earned a bachelor's degree in violin performance from the Eastman School of Music and a master's degree in music composition from Yale, initially set out to use a MIDI violin for his compositions, but found it wanting in several ways. The MIDI violin works by transmitting information about how violin strings vibrate to a digital synthesizer, which uses software to reproduce the sound. The system is unresponsive and prone to error, Nichols said. For one thing, there's often a substantial delay between the time a string is bowed and its vibration is translated into MIDI pitch and velocity information, he said. This results in a gap between the performance gesture and the sound, and rapid changes in bow direction and pitch often are not translated.

So Nichols set out to build a violin that did not depend on MIDI but instead sent data almost instantaneously from multiple sensors into a computer. "The vBow has really good resolution, which means that it senses really accurately all of my motions," he said. "So you can hear that as I draw the vBow at a regular speed, I get a clear violin sound. But if I draw the vBow too quickly, you can hear that it's as if the bow is skimming over the top of the string and just playing the higher partials or frequencies of the sound. And if I draw the vBow too slowly, it's as if the bow doesn't get the string to vibrate."

Haptic feedback has been used extensively by scientists experimenting with virtual reality and robotics. Technology magazines these days are filled with pictures of people wearing futuristic-looking gloves to control a robotic arm, which, when it closes its metallic fingers around an object, will communicate the resistance of that object back to the glove-wearer.

For musicians, the feeling of an instrument is key to their ability to express a note in a particular way. Witness, say, the dramatic antics of Geoff Nuttall, a violinist with the St. Lawrence String Quartet (Stanford's ensemble-in-residence), or the contortions of a jazz pianist trying to hit a chord in just the right way. A musician's rapport with his instrument is intimately physical.

"An electronic instrument that doesn't take into account how the player responds to the feeling of playing it is really missing half the interface," Nichols said. "Originally, the vBow was going to be an instrument that just used sensors to track my bow position, but then I learned about haptic feedback. So as you're moving the bow back and forth, you can feel a vibration and friction; as you're moving the bow in rotation across the virtual strings, you can feel the détentes of the string crossings; and as you're moving vertically into the string, you can feel the elasticity -- the springiness -- of the strings."

Nichols still has a way to go before his vViolin is completed. For one thing, he has yet to develop the vStrings for controlling pitch (although he has already built the fingerboard). He also must construct the vBody. These projects, he predicts, will take a few years.

Meanwhile, he will begin work at the end of the month as an assistant professor of composition and music technology at the University of Montana, where he was hired in July.


By John Sanford

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