Improving the Chamberlin Digital State Variable Filter
This work addresses incremental improvements for electronic music applications using digital filters.
The paper tackled issues in the Chamberlin digital state variable filter by deriving transfer functions from a modified block diagram and developing improved filter equations to better shape the filter spectrum, comparing it to an alternative time-domain approach that yields similar results.
The state variable filter configuration is a classic analogue design which has been employed in many electronic music applications. A digital implementation of this filter was put forward by Chamberlin, which has been deployed in both software and hardware forms. While this has proven to be a straightforward and successful digital filter design, it suffers from some issues, which have already been identified in the literature. From a modified Chamberlin block diagram, we derive the transfer functions describing its three basic responses, highpass, bandpass, and lowpass. An analysis of these leads to the development of an improvement, which attempts to better shape the filter spectrum. From these new transfer functions, a set of filter equations is developed. Finally, the approach is compared to an alternative time-domain based re-organisation of update equations, which is shown to deliver a similar result.