Methods of Extending a Generalized Sidelobe Canceller With External Microphones

While substantial noise reduction and speech enhancement can be achieved with multiple microphones organized in an array, in some cases, such as when the microphone spacings are quite close, it can also be quite limited. This degradation can, however, be resolved by the introduction of one or more external microphones (<inline-formula><tex-math notation="LaTeX">$\text{XM}$</tex-math></inline-formula>s) into the same physical space as the local microphone array (<inline-formula><tex-math notation="LaTeX">$\text{LMA}$</tex-math></inline-formula>). In this paper, three methods of extending an <inline-formula><tex-math notation="LaTeX">$\text{LMA}$</tex-math></inline-formula>-based generalized sidelobe canceller (<inline-formula><tex-math notation="LaTeX">$\text{GSC-LMA}$</tex-math></inline-formula>) with multiple <inline-formula><tex-math notation="LaTeX">$\text{XM}$</tex-math></inline-formula>s are proposed in such a manner that the relative transfer function pertaining to the <inline-formula><tex-math notation="LaTeX">$\text{LMA}$</tex-math></inline-formula> is treated as <italic>a priori</italic> knowledge. Two of these methods involve a procedure for completing an extended blocking matrix, whereas the third uses the speech estimate from the <inline-formula><tex-math notation="LaTeX">$\text{GSC-LMA}$</tex-math></inline-formula> directly with an orthogonalized version of the <inline-formula><tex-math notation="LaTeX">$\text{XM}$</tex-math></inline-formula> signals to obtain an improved speech estimate via a rank-1 generalized eigenvalue decomposition. All three methods were evaluated with recorded data from an office room and it was found that the third method could offer the most improvement. It was also shown that in using this method, the speech estimate from the <inline-formula><tex-math notation="LaTeX">$\text{GSC-LMA}$</tex-math></inline-formula> was not compromised and would be available to the listener if so desired, along with the improved speech estimate that uses both the <inline-formula><tex-math notation="LaTeX">$\text{LMA}$</tex-math></inline-formula> and <inline-formula><tex-math notation="LaTeX">$\text{XM}$</tex-math></inline-formula>s.