Patent ID: 7895040
Filing Date: 2011-02-22
Classification: G10L

Abstract:
1. An apparatus for recognizing voice from a supplied voice signal using a HMM (Hidden Markov Model) comprising: an acoustic processing unit configured to acquire voice characteristic vectors for each of frames having a constant time width from the voice signal; a standard frame storage unit configured to determine one of the frames as a standard frame and store a frame number of the standard frame; a standard frame renewing, unit configured to, when a predetermined number of frames have passed over from the standard frame, reset and renew the standard frame to a frame which comes the predetermined number of frames after the standard frame, and repeat such resetting and renewing through last frame in sequence; a first search range selecting unit configured to select a first search range of the HMM on basis of a beam search for the standard frame; a first output probability calculating unit configured to calculate first output probabilities of voice characteristic vectors in respective transition paths within the first search range; a first output probability storage unit configured to store the first output probabilities as combined with the respective transition paths; a first output probability erasing unit configured to erase all the first output probabilities stored as combined with the transition paths when the standard frame is renewed; a second search range selecting unit configured to select a second search range of the HMM in the each of frames on basis of the beam search for the each of frames within an interval from the standard frame to a next and new standard frame, when the standard frame is not yet renewed; a second output probability calculating unit configured to calculate second output probabilities of the voice characteristic vectors in the current frame, of the voice characteristics vectors in the current frame or the standard frame, of the transition paths, when the first output probabilities as well as the second output probabilities in an interval from the standard frame to a frame immediately before a current frame are not yet stored; a determining unit configured to determine whether the first output probabilities in the respective transition paths within the second search range in the current frame or the second output probabilities relating to past frames existing between the standard frame and the current frame are combined with the transition paths; an approximate value setting unit configured to set the first output probabilities relating to the past frames between the standard frame and the current frame or the second output probabilities as approximate values of the second output probabilities of the transition paths when the first output probabilities or the second output probabilities relating to the past frames between the standard frame and the current frame are already stored as available; a second output probability storage unit configured to store the second output probabilities anew combined with the transition paths; a second output probability erasing unit configured to erase all the second output probabilities stored as combined with the transition paths when the standard frame is renewed; a forward probability calculating unit configured to calculate the forward probabilities of the current frame from the forward probabilities of previous frame calculated in advance, all the approximate values of the current frame and all the second output probabilities; and a voice recognizing unit configured to calculate the forward probabilities of the respective HMMs until the last frame and then provides a category assigned to the HMM which provides a largest forward probability for the last frame as a result of the voice recognition.