For various reasons including the reduction of computational costs many source

For various reasons including the reduction of

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For various reasons, including the reduction of computational costs, many source-localization algorithms break the array into pairs of microphones (See Section 1.1 for references of work in this area.). Pairwise time-delay estimation (TDE) is used to determine the time difference of arrival (TDOA) of speech sounds between the microphones comprising each pair. The redundancy of a multitude of TDOA estimates has been exploited by statistically averaging in some way to give an estimate of the talker’s location [12]. However, pairwise techniques suffer considerably from acoustic reverberation. The performance of pairwise techniques improves with the amount of data used, but the desire for high update rates and low latency places strict limits on this. 2
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When a system has a multitude of microphones, far more than a sufficient number for source- localization, they should be used in a manner that will make the algorithm robust to reverberation. The application of error-prone pairwise TDE does not seem to be the best way to achieve this. An alternative approach is one where a beamformer is used to search over a predefined spatial region looking for a peak (or peaks) in the power of its output signal [59]. While this is computationally more intensive than pairwise methods, it inherently combines the signals from multiple microphones rather than reducing the data from each pair to a single time-delay parameter. This approach is able to compensate for the short duration of each data segment used for localization by integrating the data from many, or all, of the microphones prior to parameter estimation. An additional advantage that beam-steering techniques have over TDE-based techniques is the ability to localize multiple simultaneous talkers. In such a scenario, the power of a steered beamformer should peak multiple times, and each peak should correspond to the location of an active talker. Although these techniques have not been a popular choice for speech-array applications, a new steered-beamformer method is proposed in this thesis, which combines the best features of the beamformer with those of a popular pairwise technique. It will be demonstrated that this new steered-beamformer produces highly reliable location estimates, in rooms with reverberation times of 200 and 400 milliseconds, using 25-millisecond data segments. 1.1 Methods for Pairwise Time-Delay Estimation Many passive talker localization techniques rely on pairwise time delay estimation (TDE) [11][13][64]. These techniques use the time difference of arrival (TDOA) of speech sounds between two spatially separated microphones to parameterize the source location [7][8][12][20][93]. The best results are obtained when the microphone pairs are strategically positioned to give optimal spatial accuracy [9][10].
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