  We propose a diarization system, that estimates "who spoke when" based on
spatial information, to be used as a front-end of a meeting transcription
system running on the signals gathered from an acoustic sensor network (ASN).
Although the spatial distribution of the microphones is advantageous,
exploiting the spatial diversity for diarization and signal enhancement is
challenging, because the microphones' positions are typically unknown, and the
recorded signals are initially unsynchronized in general. Here, we approach
these issues by first blindly synchronizing the signals and then estimating
time differences of arrival (TDOAs). The TDOA information is exploited to
estimate the speakers' activity, even in the presence of multiple speakers
being simultaneously active. This speaker activity information serves as a
guide for a spatial mixture model, on which basis the individual speaker's
signals are extracted via beamforming. Finally, the extracted signals are
forwarded to a speech recognizer. Additionally, a novel initialization scheme
for spatial mixture models based on the TDOA estimates is proposed. Experiments
conducted on real recordings from the LibriWASN data set have shown that our
proposed system is advantageous compared to a system using a spatial mixture
model, which does not make use of external diarization information.
