1. An apparatus for producing an acoustic model for speech recognition, said apparatus comprising: means for categorizing a plurality of first noise samples into clusters, a number of said clusters being smaller than that of noise samples; means for selecting a noise sample in each of the clusters to set the selected noise samples to second noise samples for training; means for storing thereon an untrained acoustic model for training; and means for training the untrained acoustic model by using the second noise samples for training so as to produce the acoustic model for speech recognition.