A digital filter circuit for filtering at least two input signals having different signal data rates is described. The digital filter circuit includes an input multiplexer sub-circuit, a digital filter, and an output multiplexer sub-circuit. The digital filter is connected to the input multiplexer sub-circuit downstream of the input multiplexer sub-circuit. The digital filter is connected to the output multiplexer sub-circuit upstream of the output multiplexer sub-circuit. The input multiplexer sub-circuit is configured to receive the at least two input signals having different signal data rates. The input multiplexer sub-circuit is configured to selectively forward the at least two input signals to the digital filter. The digital filter is configured to filter the at least two input signals, thereby obtaining at least two filtered input signals. The output multiplexer sub-circuit is configured to selectively output the at least two filtered input signals. Further, a measurement instrument and a signal processing method are described.

A method for optimizing processor operation in a processing system including one or more digital filters is provided according to the invention. The method includes generating initial filter coefficients for the one or more digital filters of the processing system, determining one or more initial filter coefficients for at least one digital filter of the one or more digital filters that can be dropped and dropping the one or more initial filter coefficients. Dropping the one or more initial filter coefficients reduces a total number of filter coefficients to be used by the processing system.