  To estimate the direction of arrival (DOA) of multiple speakers with methods
that use prototype transfer functions, frequency-dependent spatial spectra
(SPS) are usually constructed. To make the DOA estimation robust, SPS from
different frequencies can be combined. According to how the SPS are combined,
frequency fusion mechanisms are categorized into narrowband, broadband, or
speaker-grouped, where the latter mechanism requires a speaker-wise grouping of
frequencies. For a binaural hearing aid setup, in this paper we propose an
interaural time difference (ITD)-based speaker-grouped frequency fusion
mechanism. By exploiting the DOA dependence of ITDs, frequencies can be grouped
according to a common ITD and be used for DOA estimation of the respective
speaker. We apply the proposed ITD-based speaker-grouped frequency fusion
mechanism for different DOA estimation methods, namely the multiple signal
classification, steered response power and a recently published method based on
relative transfer function (RTF) vectors. In our experiments, we compare DOA
estimation with different fusion mechanisms. For all considered DOA estimation
methods, the proposed ITD-based speaker-grouped frequency fusion mechanism
results in a higher DOA estimation accuracy compared with the narrowband and
broadband fusion mechanisms.
