Patent ID: 7756707

Claim:
A speech signal processing apparatus comprising: a dividing unit which divides an input speech signal into frames, each of which has a predetermined time length; a calculation unit which calculates a VAD metric for a current frame; a determination unit which determines whether a signal in the current frame contains speech or non-speech by using the VAD metric and outputs a VAD flag of 1 or 0 indicating whether the current frame contains speech or non-speech, respectively; a filter unit which smooths the VAD flags output from said determination unit, wherein said filter unit executes a filter process expressed as follows: V f = ρV f−1 +(1−ρ) X f , where: f is a frame index; V f is the filter output of the frame f; X f is the filter input of the frame f, which is the VAD flag of the frame f; and ρ is a constant value as a pole of the filter; and a state evaluation unit which, according to the output from said filter unit, V f , evaluates a current state of the speech signal from among a silence state, a speech state, a possible speech state representing an intermediate state from the silence state to the speech state, and a possible silence state representing an intermediate state from the speech state to the silence state, wherein said state evaluation unit performs the following operations: in the silence state, when the VAD flag becomes 1, the state moves to the possible speech state, in the possible speech state, when V f exceeds a first threshold value, the state moves to the speech state and V f is set to 1, and when V f is below a second threshold value that is smaller that the first threshold value, the state moves to the silence state, in the speech state, when the VAD flag becomes 0, the state moves to the possible silence state, and in the possible silence state, when V f is below the second threshold value, the state moves to the silence state and V f is set to 0, and when the VAD flag becomes 1, the state moves to the speech state.