Automated Physical Modeling of Nonlinear Audio Circuits for Real-Time Audio Effects-Part II: BJT and Vacuum Tube Examples

• Published in: IEEE transactions on audio, speech, and language processing Vol. 20; no. 4; pp. 1207 - 1216
• Main Author: Yeh, D. T.
• Format: Journal Article
• Language: English
• Published: Piscataway, NJ IEEE 01.05.2012; Institute of Electrical and Electronics Engineers
• Subjects: Applied sciences; Circuit simulation; Computational modeling; Detection, estimation, filtering, equalization, prediction; Electron tubes; Exact sciences and technology; Function approximation; guitar amplifier modeling; guitar distortion; Information, signal and communications theory; Integrated circuit modeling; K-Method; Mathematical model; nonlinear filters; ordinary differential equation (ODE) solver; physical modeling synthesis; real-time audio; Real-time systems; Signal and communications theory; Signal, noise; Telecommunications and information theory; vacuum tube amplifier; virtual analog; Voltage control; Differential equation; vacuum tube amplifier; Non linear filter; guitar distortion; Triode; Function approximation; physical modeling synthesis; Modeling; Non linear phenomenon; Variable transformation; Preamplifier; K-Method; Off line; SPICE; virtual analog; Linear interpolation; Circuit simulation; real-time audio; nonlinear filters; Non linear system; Bipolar transistor; ordinary differential equation (ODE) solver; Simulation; guitar amplifier modeling; Non linear effect; Musical instrument
• ISSN: 1558-7916; 1558-7924
• DOI: 10.1109/TASL.2011.2173677

This is the second part of a two-part paper that presents a procedural approach to derive nonlinear filters from schematics of audio circuits for the purpose of digitally emulating musical effects circuits in real-time. This work presents the results of applying this physics-based technique to two audio preamplifier circuits. The approach extends a thread of research that uses variable transformation and offline solution of the global nonlinear system. The solution is approximated with multidimensional linear interpolation during runtime to avoid uncertainties in convergence. The methods are evaluated here experimentally against a reference SPICE circuit simulation. The circuits studied here are the bipolar junction transistor (BJT) common emitter amplifier, and the triode preamplifier. The results suggest the use of function approximation to represent the solved system nonlinearity of the K-method and invite future work along these lines.