| Hands-free speech communication is indispensable in audio and video conference systems, hot-line telephones and videophones, mobile radio terminals and digital ISDN network etc. However, the control(cancellation) of the acoustic echo has always had a strong impact on the transmission quality in hands-free telecommunication.Conventional methods of acoustic echo control (cancellation),such as echo suppression or gain control, may lead to the degradations in speech quality or make the speakers feel uncomfortable.Adaptive echo cancellation provides a comfortable solution whose concept is extremely simple: If an exact electric replica of the LRM (Loudspeaker-Room-Microphone) system is provided, the decoupling "of loudspeaker and microphone can be achieved without any restrictions to the electric acoustic system, and more important ,without any loss of convenience to the user.The implementation of such a system is extremely complicated due to three factors: the impulse response of a LRM system has a duration of several hundred milliseconds, the system has to be adaptive, and the adaptation has to be performed with a speech input. The traditional adaptive algorithms such as LMS and NLMS can not obtain the satisfied result in the real-time acoustic echo cancellation processing.The Decorrelating NLMS with Variable Step Size algorithm has provided thepossibility of the real-time acoustic echo cancellation .It features better steady-state misalignment of variable step size method and the faster convergence rate of the decorrelating method than those of the NLMS algorithm. Computer simulation results confirm the effectiveness of this algorithm.Furthermore, an acoustic echo cancellation system has been made using TMS320VC5402 and some other devices . The Decorrelating NLMS with Variable Step Size algorithm has been implemented on this system in the real-time processing. It has been proved that Decorrelating NLMS with Variable Step Size algorithm can obtain a satisfied echo cancellation result.
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