1. A system for detecting reconizability of an input signal, applicable to the front stage of a speech recognition device or a dialog device, comprising: an environment parameter generator to generate at least an environment parameter from an input signal; a signal recognition verifier to verify whether said input signal being recognizable in accordance with said environment parameters after initial training with environment parameters in advance; and a strategy response processor; wherein said input signal is passed to said speech recognition or dialog device when said input signal is verified as recognizable; while said strategy response processor is triggered to respond with a plurality of strategies when said input signal is verified as unrecognizable.