A method steering a null toward a point in high reverberate non-minimum phase acoustic space

In this paper, we propose a method capable of steering a null toward a point in high reverberate non-minimum phase acoustic space. This method is characterized by applying the cascade connection of recursive and non-recursive adaptive filters to steering the null. The cascade connection completely expresses the structure of the acoustic paths from a sound source to microphones. The acoustic paths can thereby estimated with high precision. However, as well known, the recursive adaptive filter has two problems. One is that the performance of the recursive adaptive filter is apt to become unstable. We solve this problem by applying the lattice structure to the recursive adaptive filter. The stable performance is guaranteed by limiting the reflection coefficients to less than unity. Another is that the response of the recursive filter diverges when the minimum phase condition is not satisfied. We hence separate the recursive filter into the minimum and the non-minimum phase components. We next transform the latter into a non-recursive filter and connect it to the output of another microphone. The cascade connection can thereby steer the null with high stability and precision even in high reverberate non-minimum phase acoustic space.