Speaker localization by humanoid robots in reverberant environments

One of the important tasks of a humanoid-robot auditory system is speaker localization. It is used for the construction of the surrounding acoustic scene and as an input for additional processing methods. Localization is usually required to operate indoors under high reverberation levels. Recently, an algorithm for speaker localization under these conditions was proposed. The algorithm uses a spherical microphone array and the processing is performed in the spherical harmonics domain, requiring a relatively large number of microphones to efficiently cover the entire frequency range of speech. However, the number of microphones in the auditory system of a humanoid robot is usually limited. The current paper proposes an improvement of the previously published algorithm. The improvement aims to overcome the frequency limitations imposed by the insufficient number of microphones. The improvement is achieved by using a novel space-domain distance algorithm that does not requires the transformation to the spherical harmonics domain, thereby avoiding the frequency range limitations. A numerical study shows two important results. The first is that, using the improved algorithm, the operation frequency range can be significantly extended. The second important result is related to the fact that higher frequencies contain more detailed information about the surrounding sound field. Hence, the additional higher frequencies lead to improved localization accuracy.