1. A voice activity detector for detecting the presence of speech segments in frames of an input signal, the detector comprising: a frame divider for dividing frames of the input signal into consecutive sub-frames; an energy level estimator for estimating an energy level of the input signal in each of the consecutive sub-frames; a noise eliminator for analyzing the estimated energy levels of sets of the sub-frames to detect and to eliminate from energy level enhancement noise sub-frames and to indicate remaining sub-frames as speech sub-frames for energy level enhancement, and an energy level enhancer for enhancing the energy level estimated by the energy level estimator for each of the indicated speech sub-frames by an amount which relates to a detected change of the estimated energy level for a current indicated speech sub-frame relative to that for neighbouring indicated speech sub-frames.