Patent ID: 8744846

Claim:
A noise state determination method of a noisy speech signal, the method comprising: calculating a transformed spectrum by transforming an input noisy speech signal to a frequency domain; calculating a smoothed magnitude spectrum by reducing magnitude differences of the transformed spectrum between neighboring frames; calculating a search spectrum which represents an estimated noise component of the smoothed magnitude spectrum; and calculating an identification ratio which represents a ratio of a noise component included in the input noisy speech signal, by using the smoothed magnitude spectrum and the search spectrum; wherein a whole frequency range of the frequency domain is divided into subbands, and the calculating of the search spectrum and the calculating of the identification ratio are performed on a sub-band basis, and wherein the search spectrum is calculated by using Equation E-1 T i,j ( f )=κ( j )· U i−1,j ( f )+(1−κ( j ))· S i,j ( f ) (E-1) wherein, i is a frame index, j (0≦j<J<L) is a sub-band index obtained by dividing a predetermined frequency range 2 L by a sub-band size (=2 L−J ), J and L are natural numbers which respectively determining a total number of the sub-bands and the predetermined frequency range, T i,j (f) is the search spectrum, S i,j (f) is the smoothed magnitude spectrum, U i−1,j (f) is a weighted spectrum indicating a spectrum having a smaller magnitude between the search spectrum and the smoothed magnitude spectrum of the previous frame, and κ(j) (0<κ(J−1)≦κ(j)≦κ(0)≦1) is a differential forgetting factor.