Wave digital filters: Voltage, current, or power waves?

Wave digital filters (WDF\´s) may be derived from analog reference filters by voltage, current, or power waves. While current waves do not lead to structures essentially different from those derived by the common voltage waves, power wave structures have usually been disregarded due to their computational complexity. It is shown that, on the contrary, some of these structures may be implemented quite efficiently. The recursive parts of digital ladder filters, including the "normalized" Gray-Markel filter, are interpreted as voltage, current, and power WDF\´s, respectively. Finally the quasi-equivalence of the three types of WDF\´s is discussed.