Julius Smith

Early career and NeXT

From 1986 to 1991, Smith was a founding member of the Sound and Music Group at NeXT Computer, where he developed real-time signal-processing software for the Music Kit, Sound Library, and other audio software for the NeXTSTEP platform.^{[6] [7]}

Academic career

Smith joined the Stanford faculty in 1991, becoming an associate professor in 1994, full professor in 2004, and professor emeritus in 2022.^[1] At Stanford, he has taught courses in digital signal processing, computer music, and acoustics, while mentoring numerous graduate students who have gone on to careers in academia and industry.

He has held visiting appointments at the Télécom Polytechnic Institute of Paris, IRCAM Scientific Council in Paris, and Helsinki University of Technology, where he collaborated closely with Finnish acoustician and engineer Matti Karjalainen.^[8]

Industry involvement

Beyond academia, Smith has worked with several audio-technology companies, including:

• Staccato Systems – developed physical modeling synthesis technology licensed by Analog Devices
• Shazam Entertainment – co-invented the core audio fingerprinting algorithm^[3]
• moForte – continued development of physical modeling technologies^[9]

Digital waveguide synthesis

Smith's most influential contribution is digital waveguide synthesis, a computationally efficient method for simulating the physics of musical instruments. This technique models wave propagation in strings, tubes, and membranes using digital delay lines and filters. His 1992 Computer Music Journal article formalizing this approach remains a foundational text in the field.^[10]

Spatial localization

Smith's 1987 paper "Closed-Form Least-Squares Source Location Estimation from Range-Difference Measurements" introduced an algebraic solution to the time-difference-of-arrival (TDOA) localization problem. This work has been cited over 1,000 times and is fundamental to applications in radar, sonar, and wireless communications.^[11]

Sampling-rate conversion

At ICASSP 1984, Smith introduced windowed-sinc interpolation for high-quality, time-varying sampling-rate conversion. This method has been widely adopted in commercial sample-rate converters^[12] and open-source software such as libsamplerate.^[13]

Educational contributions

Smith has authored four open-access textbooks that are widely used in graduate-level audio DSP courses:^[14]

• Mathematics of the Discrete Fourier Transform (2007)
• Introduction to Digital Filters (2007)
• Physical Audio Signal Processing (2010)
• Spectral Audio Signal Processing (2011)

Books

• Smith, Julius O. (2007). Mathematics of the Discrete Fourier Transform (DFT): With Audio Applications (2nd ed.). W3K Publishing. ISBN 978-0-9745607-4-8.
• Smith, Julius O. (2007). Introduction to Digital Filters: With Audio Applications. W3K Publishing. ISBN 978-0-9745607-1-7.
• Smith, Julius O. (2010). Physical Audio Signal Processing: For Virtual Musical Instruments and Audio Effects. W3K Publishing. ISBN 978-0-9745607-2-4.
• Smith, Julius O. (2011). Spectral Audio Signal Processing. W3K Publishing. ISBN 978-0-9745607-3-1.

Key papers

• Smith, Julius O. (1992). "Physical Modeling Using Digital Waveguides". Computer Music Journal. 16 (4): 74–91. doi:10.2307/3680470. JSTOR 3680470.
• Smith, Julius O.; Abel, Jonathan S. (1987). "Closed-Form Least-Squares Source Location Estimation from Range-Difference Measurements". IEEE Transactions on Acoustics, Speech, and Signal Processing. 35 (12): 1661–1669. doi:10.1109/TASSP.1987.1165089.
• Smith, Julius O. (1983). Techniques for Digital Filter Design and System Identification with Application to the Violin (Ph.D. dissertation). Stanford University.