1. A method for distinguishing speech with a voice activity detector including a processor and a memory, the method comprising: dividing, via the processor, an input voice signal into a plurality of frames; obtaining, via the processor, parameters from the divided frames; modeling, via the processor, a probability density function of a feature vector in state j for each frame using the obtained parameters; obtaining, via the processor, a maximum probability P 0 of each state that a corresponding frame will be a noise frame and a maximum probability P 1 of each state that the corresponding frame will be a speech frame from the modeled PDF and obtained parameters; performing, via the processor, a hypothesis test to determine whether the corresponding frame is a noise frame or speech frame using the obtained probabilities P 0 and P 1 ; and storing data corresponding to the determined speech frame in the memory.