Patent ID: 7680656

Claim:
A method of determining an estimate for a noise-reduced value representing a portion of a noise-reduced speech signal, the method comprising: generating an alternative sensor signal using an alternative sensor; generating an air conduction microphone signal; using the alternative sensor signal and the air conduction microphone signal to estimate a likelihood, L(S t ) of a speech state, S t by estimating a separate likelihood of the speech state for each of a set of frequency components and combining the separate likelihoods to form the likelihood of the speech state; and using the likelihood of the speech state to estimate the noise-reduced value, {circumflex over (X)} t , as: X ^ t = ∑ s ∈ { S } ⁢ ⁢ π s ⁢ E ⁡ ( X t ❘ Y t , B t , S t = s ) where π s is a posterior on the state and is given by: π s = L ⁡ ( S t = s ) ∑ s ∈ { S } ⁢ ⁢ L ⁡ ( S t = s ) and where: E ⁡ ( X t ❘ Y t , B t , S t = s ) = σ s 2 ⁡ ( σ p 2 ⁢ Y t + M * ( ( σ u 2 + g 2 ⁢ σ v 2 ) ⁢ B t - g 2 ⁢ σ v 2 ⁢ GY t ) σ p 2 ⁡ ( σ u 2 + g 2 ⁢ σ v 2 + σ s 2 ) +  M  2 ⁢ σ s 2 ⁡ ( σ u 2 + g 2 ⁢ σ v 2 ) ) where : ⁢ σ p 2 = σ w 2 + g 2 ⁢ σ v 2 ⁢ σ u 2 σ u 2 + g 2 ⁢ σ v 2 ⁢  G  2 ⁢ ⁢ and M = H - g 2 ⁢ σ v 2 σ u ⁢ 2 + g 2 ⁢ σ v 2 ⁢ G where M* is the complex conjugate of M, X t is a noise reduced value, Y t is a value for a frame t of the air conduction microphone signal, B t is a value for a frame t of the alternative sensor signal, σ u 2 is a variance of sensor noise in the air conduction microphone, σ w 2 is a variance of sensor noise in the alternative sensor, g 2 σ v 2 is the variance of ambient noise, G is the channel response of the alternative sensor to ambient noise, H is the channel response of the alternative sensor to a clean speech signal, S is the set of all speech states, σ s 2 is a variance for a distribution that models a probability of a noise-reduced value given a speech state and E(X t |Y t ,B t ,S t =s) is the expectation of X t given Y t , B t , and a speech state of s.