1. An echo path monitoring system comprising: a comparison generator configured to compare a microphone signal including an echo of a far-end signal with an estimated echo generated by an adaptive filter to obtain a first comparison, and to compare an error signal, which represents a difference between the microphone signal and the estimated echo, with the estimated echo to obtain a second comparison; and a controller configured to combine the first and second comparisons to form a parameter indicative of a state of the microphone signal and, in dependence on said parameter, control an operating mode of the adaptive filter.