From Event: SPIE Optical Engineering + Applications, 2016
Virtual analog modeling is the process of creating a digital model of an analog system. In this work a virtual analog model of a dynamic range compression circuit for electrical guitars is constructed by analyzing and measuring the analog reference system. The particular property of the chosen compression system is the use of an analog optical isolator, also called optocoupler. It is a two-port circuit element used to electrically isolate different parts of the audio system while maintaining one-directional coupling via the optical channel. The used analog optical isolator was a Perkin Elmer VTL5C2, consisting of a light dependent resistor and a light emitting diode in an opaque enclosure. All the characteristics of the nonlinear elements were measured, especially the VTL5C2, then the circuit was analyzed to determine its static behavior. In the digital model the output signal is multiplied with a timevariant gain factor, which is dependent on the input signal. Several processing blocks are used to calculate the gain factor, emulating the static and dynamic behavior of the analog reference system. An iterative error minimization procedure is used to refine parameters for the digital model. Finally the output of digital model and analog reference are compared to show how well the model has been adapted to the reference device.
Felix Eichas and Udo Zölzer, "Modeling of an optocoupler-based audio dynamic range control circuit," Proc. SPIE 9948, Novel Optical Systems Design and Optimization XIX, 99480W (Presented at SPIE Optical Engineering + Applications: August 30, 2016; Published: 30 September 2016); https://doi.org/10.1117/12.2235686.
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