A method and system for using input signal quality in an automatic speech recognition system. The method includes measuring the quality of an input signal into a speech recognition system and varying a rejection threshold of the speech recognition system at runtime in dependence on the measurement of the input signal quality. If the measurement of the input signal quality is low, the rejection threshold is reduced and, if the measurement of the input signal quality is high, the rejection threshold is increased. The measurement of the input signal quality may be based on one or more of the measurements of signal-to-noise ratio, loudness, including clipping, and speech signal duration.