Patent ID: 6130943
Filing Date: 2000-10-10
Classification: H04B

Abstract:
An apparatus for suppressing echo in a telecommunications network having a send path carrying a voice signal and a receive path carrying the echo, the apparatus comprising:a first filter coupled to the send path for producing a transformed send path signal having selected frequencies attenuated, the first filter including:a first sample buffer for receiving and storing 2.sup.n digitized samples of the send path signal, wherein n is an integer greater than 0,a first processor implementing a discrete, real-valued Fourier transform of the contents of the sample buffer, which circumvents problems introduced by reliance on Fourier transforms with complex coefficients,a first multiplier that attenuates one set of frequencies in the voice spectrum according to the rule that if a frequency in the voice spectrum is attenuated then the first harmonic of that frequency is not attenuated, and if the first harmonic of a frequency in the voice spectrum is attenuated then that frequency is not attenuated, anda second processor implementing a discrete, real-valued inverse Fourier transform of the power of the voice frequency spectrum after selective attenuation by the first multiplier, to produce digitized samples of the transformed send path signal wherein all frequencies modeled have the same phase; anda second filter coupled to the receive path for producing a transformed receive path signal having selected frequencies attenuated, the second filter including:a second sample buffer for receiving and storing 2.sup.n digitized samples of the reccive path signal,a third processor implementing a discrete, real-valued Fourier transform of the contents of the second sample buffer, which circumvents problems introduced by reliance on Fourier transforms with complex coefficients,a second multiplier that attenuates a complementary set of frequencies in the voice spectrum according to the rule that any frequency attenuated by the first multiplier is not attenuated by the second multiplier and any frequency not attenuated by the first multiplier is attenuated by the second multiplier, anda fourth processor implementing a discrete, real-valued inverse Fourier transform of the power of the voice frequency spectrum after selective attenuation by the second multiplier to produce digitized samples of the transformed receive path signal wherein all frequencies modeled have the same phase.