Acoustic echo cancellation or suppression for hands-free cellphones is a challenging topic. One of the biggest problems is nonlinearity of the echo-path such as loudspeaker distortion and vibrations of the cellphone shell [4, 18, 19, 28]. When a speech signal with large power is injected into a small loudspeaker, the loudspeaker itself and many mechanical contacts in the shell generate distorted echo. Among the sources of nonlinearity (distortion), mechanical nonlinearity with shell vibrations is said to be the dominant factor .
This chapter presents a nonlinear echo canceller using spectral shaping based on a frequency-domain model of highly nonlinear residual echo . In the next section, the residual-echo model based on the spectral correlation between the residual echo and the echo replica is developed from experimental results. An echo suppressor structure based on the new model is shown in Sec. 8.3. Evaluation results using a hands-free cellphone handset are demonstrated in Sec. 8.4.