Savart Journal

science and technology of stringed musical instruments

Detection of Bow Direction and Stopped String Length by Analysis of Asymmetric Helmholtz Velocity Data from a Magnetic Violin Pickup

John Silzel


The strings of bowed musical instruments undergo “Helmholtz motion” and exhibit time-varying displacements and velocities that contain information about the length of the string and the direction of action of the forces of static friction from the bow hair. This information is largely obscured in the sound radiated from acoustic instruments and in the output of pickups located on the bridge or instrument body. However, pickups that directly sense string dynamics can recover these information-rich signals from the bowed string. From the asymmetry of Helmholtz motion it is possible to deduce from pickup signal waveforms both the direction of the bow’s motion (upbow or down-bow) and the approximate length of the vibrating string as these change during a performance. Computationally simple methods applied to the output of a magnetic pickup permit recovery of aspects of a player’s bowing and left hand technique for study, or in electronic music, the control of performance parameters by bow direction or left hand position.

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Article published Jun 13, 2011.
This article has been accessed 7489 times since publication.


The Savart Journal is published in collaboration with the Guild of American Luthiers.

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John Silzel
Biola University
United States

John W. Silzel, Ph.D. developed new products and technologies for biomedical research and medical diagnostics for 18 years. He now is Associate Professor in the Department of Chemistry, Physics, and Engineering at Biola University of La Mirada, California. In addition to teaching, Dr. Silzel consults and pursues research interests which include the application of technology to the musical arts, including a software application for real time pitch recognition for bowed string instruments. His personal website is