4. The apparatus of claim 1 , wherein the normalizer is further configured to normalize the frames belonging to the current window in consideration of the frames belonging to the preceding windows and frames of training data in response to a total number of the frames belonging to the current window and of the frames belonging to the preceding windows being insufficient for speech recognition.
4. The apparatus of claim 1 , wherein the normalizer is further configured to normalize the frames belonging to the current window in consideration of the frames belonging to the preceding windows and frames of training data in response to a total number of the frames belonging to the current window and of the frames belonging to the preceding windows being insufficient for speech recognition. 5. The apparatus of claim 4 , wherein the normalizer is further configured to acquire a number of frames corresponding to a difference between the total number of the frames and a reference value from the training data in response to the total number of the frames being less than the reference value.