Improvements in or relating to state variable filters.

摘要

A programmable state variable filter includes a pair of integrators 3, 6. An electronically programmable attenuator 2, 4 in the form of a multiplying digital-to-analog converter is connected in series with the input of each integrator. The digital inputs of the converters are connected together and permit programming of the resonant or turnover frequency of the filter. There is also provided a tone detecting apparatus and a tone generating apparatus incorporating the filter.