The present disclosure relates to a system comprising: a MEMS capacitive transducer comprising a first electrode and a second electrode; integrator circuitry; and test circuitry. The MEMS capacitive transducer forms part of a negative feedback path of the integrator circuitry, and the test circuitry is operable to selectively apply one or more current sources to an input of the integrator circuitry based on a signal at an output of the integrator so as to generate a periodic signal at the output of the integrator circuitry. A frequency of the periodic signal is at least partially dependent upon a capacitance of the MEMS capacitive transducer. The system is further operative to determine a parameter indicative of the frequency of the periodic signal and to estimate the capacitance of the MEMS capacitive transducer based on the parameter indicative of the frequency of the periodic signal.