16. The speech recognition method of claim 13 , wherein the said enhancing the sound quality includes: performing fast Fourier transform on a single frame of the input speech signal; calculating a sum of signals in a specific frequency band of the fast Fourier transformed signal; dividing the sum of the signals by a number of fast Fourier transform bins; converting the divided sum into a log-scale form to extract therefrom voice activity detector characteristics; calculating filter values of the Wiener filter based on the voice activity detector characteristics; and filtering the input speech signal by using the calculated filter values.
13. A speech recognition method, comprising: determining a speed level of a moving object by using a noise signal at an initial time of speech recognition; if the speed level is equal to or lower than a specific level, enhancing sound quality of an input speech signal by extracting voice activity detection features robust against vehicular noise and applying to the input speech signal a Wiener filter using the extracted voice activity detection features; detecting start and end points of a signal having been subjected to the sound quality enhancement; eliminating sudden noise components occurring when the moving object moves based on a sudden noise Gaussian mixture model; and decoding a signal having been subjected to the sudden noise elimination by using a low-speed/medium-speed acoustic model database, and if the speed level is higher than the specific level, enhancing the sound quality of the input speech signal of the speech recognition by applying a Wiener filter using a Gaussian mixture model; detecting start and end points of a signal having been subjected to the sound quality enhancement; compensating distorted harmonic components of the signal having been subjected to end point detection based on a harmonic Gaussian mixture model; eliminating sudden noise components occurring when the moving object moves based on a sudden noise Gaussian mixture model; and decoding a signal having been subjected to the compensation and the sudden noise elimination by using a high-speed acoustic model database.