Digital filter morphing techniques exist to reduce audible transient distortion during filter frequency response change. However, such distortions are heavily dependent on signal content, frequency response settings, filter topology, interpolation scheme, and sampling rates. This paper presents an investigation into these issues, implementing various filter topologies using different input stimuli and filter state change scenarios. The paper identifies the mechanisms causing these distortions, specifying worst case filter state change scenarios. The effects of existing interpolator schemes, finite word length, and system sampling rates on signal distortion are presented. The paper provides an understanding of filter state change, critical in the design of filter morphing algorithms.
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