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A Digital Model for the Prologue Voltage Control Filter

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The Prologue polyphonic synthesizer features a voltage control filter (VCF) employing an original topology. This paper examines its circuit and extracts a flowchart, which yields a set of analog filter equations. From these, the authors were able to develop a transfer function to describe its ideal linear time-invariant form. Then a linear digital version of the filter to validate the analysis was put forward. Noting that the filter operation within the synthesizer is fairly nonlinear, a number of modifications yielding a nonlinear model of the VCF is proposed. These were compared with the outputs of the original analog filter, and it was found that they approximate them consistently.

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JAES Volume 72 Issue 1/2 pp. 79-88; January 2024
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Permalink: http://www.aes.org/e-lib/browse.cfm?elib=22380

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