Time-varying wave digital filters for modeling analog systems

The theory of wave digital filters, which are well suited to model analog networks including those containing transmission lines, is extended to the time-varying case. This allows simulation of the moving vocal tract or parametric amplifiers. A representation consistent with the physics of time-varying reactances and transmission lines requires not only time-varying filter coefficients, but also structural modifications in the n-port adaptors and reactance one-ports of the filter. The number of coefficients in the adaptors is increased, and stability and pseudopassivity are not assured.