We refer to ¿Virtual Analog¿ (VA) as a wide class of digital implementations that are modeled after nonlinear analog circuits for generating or processing musical sounds. The reference analog system is therefore typically represented by a set of blocks that are connected with each other through electrical ports, and usually exhibits a nonlinear behavior. It therefore seems quite natural to consider Nonlinear Wave Digital modeling as a solid approach for the rapid prototyping of such systems. In this paper, we discuss how nonlinear wave digital modeling can be fruitfully used for this purpose, with particular reference to special blocks and connectors that allow us to overcome the implementational difficulties and potential limitations of such solutions. In particular, we address some issues that are typical of VA and physical modeling, concerning how to accommodate special blocks into WD structures, how to enable the interaction between different WD structures, and how to accommodate structural and topological changes on the fly.

In this letter, we show that a computable tree-like interconnection of parallel/series wave digital (WD) adaptors with memory (i.e., characterized by reflection filters instead of reflection coefficients) is equivalent to a like interconnection of standard (memoryless) adaptors whose peripheral ports are connected to mutators (two-port adaptors with memory). In proving all this, we provide a methodology for "extracting the memory" from a macro-adaptor, which can be fruitfully employed to simplify the implementation of WD structures