1. A speech recognition method comprising the steps of: (a) receiving input speech from a user; (b) processing the input speech using a first grammar to obtain parameter values of a first N-best list of vocabulary; (c) comparing at least one parameter value of a top result of the first N-best list to at least one predetermined threshold value; and (d) subsequently processing the input speech using a second grammar to obtain parameter values of a second N-best list of vocabulary, if the compared at least one parameter value is below the at least one predetermined threshold value.