3D echo cancellation in a home environment

Abstract

This thesis describes the work done to research, implement, and compare various algorithms for the cancellation of echoes in a home environment, where the room impulse response is unknown and variable. The general problem, where the speaker's movements are completely unrestricted, is a very hard one, and research in this area has only begun in the last several years. Therefore, this thesis addresses a simplified version of the problem, where the impulse response of the multipath environment is assumed to be stationary within the duration of a verbal command. Given this assumption, which is reasonable for most situations, algorithms based on the complex cepstrum, autocorrelation, and delay and sum methods of echo cancellation were chosen and developed for the study. Many simulation tests were done to determine the behavior of the algorithms under different echo environments. The test signals were based on the simple delay and attenuation echo model with one microphone, and on a more realistic echo model, generated by the Cool Edit Pro software, with one or three microphones. The performance metrics were the number of errors and the percent of improvement in speech recognition by Dragon Systems' Naturally Speaking software. The results showed vast improvement for the cepstral domain methods on the simple echo signals, but the numbers were mixed for the complex model, one microphone cases. However, with three microphones, the delay and sum algorithm showed consistent improvement. Given that research in this specific area of 3D echo cancellation in a home environment, where 3D refers to the moving speech source, is still in its early stage, the results are encouraging.