A method for detecting speech using a first microphone adapted to produce a first signal (x), and a second microphone adapted to produce a second signal (x2), the method comprising the steps of: (i) applying gain to the second signal to produce a normalised second signal, which signal is normalised relative to the first signal; (ii) constructing one or more signal components from the first signal and the normalised second signal; (iii) constructing an adaptive differential microphone (ADM) having a constructed microphone response constructed from the one or more signal components which response has at least one directional null; (iv) producing one or more ADM outputs (yf, yb) from the constructed microphone response in response to detected sound; (v) computing a ratio of a parameter of either a first signal component or a constructed microphone response to a parameter of an output of the ADM; (vi) comparing the ratio to an adaptive threshold value; (vii) detecting speech if the ratio is greater than or equal to the adaptive threshold value.