Resolving delay-free loops in recursive filter structures has been a longstanding problem approached in several different ways including signal flow graph manipulation ,  and more recently with Zavalishin’s instantaneous response technique ,. Härmä demonstrates a method for resolving delay-less loops in recursive filter structures  but the technique is limited to a specific generic loop topology in which the feedforward branch does not implement signal processing; all processing is implemented in one or more delay-less feedback loops. We modify Härmä’s method to accommodate filter processing in the feedforward branch and provide a step-by-step method to resolve delay-less loops in recursive filter structures. We conclude with examples including a new method of synthesizing fourth order filters.
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