Patent ID: 7315623

Claim:
A method of suppressing ambient noise in a hands-free device having two microphones spaced a predetermined distance apart, each of which supplies a microphone signal, comprising: generating a sum signal and a difference signal of the two microphone signals; computing a first Fourier transform R(f) of the sum signal (S) and a second Fourier transform of the difference signal; detecting speech pauses from the first and second Fourier transforms R(f) and D(f); determining first spectral power density S rr from the first Fourier transform R(f) of the sum signal (S); determining second spectral power density S DD from the second Fourier transform D(f) of the difference signal (D); calculating the transfer function H T (f) for an adaptive transformation filter from the first spectral power density S rr , and from the second spectral power density S DD ; generating the interference power density S nn (f) by multiplying the second power density S DD by its transfer function H T (f); calculating the transfer function H sub (f) of a spectral subtraction filter from the interference power density S nn (f) and from the first spectral power density S rr ; filtering the first Fourier transform R(f) with the spectral subtraction filter; and transforming the output signal of the spectral subtraction filter back to the time domain.