Samenvatting

The use of wireless acoustic sensor networks
(WASNs) has received increased attention over the last decade.
The advantages of WASNs over stand-alone multi-microphone
devices are that the microphone array is not anymore limited
by the dimensions of a single device, and that microphones
can be placed at arbitrary locations. One of the disadvantages,
however, is that for many applications, like beamforming, the
clocks of all devices in the network need to be synchronised
and that the microphone gains need to be equalised. In this
paper we will prove that a specific class of beamformers is
clock-offset and gain mismatch invariant. The parameters for
these beamformers (acoustic transfer function and power spectral
density matrices) can be estimated directly from the uncalibrated
microphone signals, instead of first synchronising the clocks and
equalising the gains and then estimating them. The resulting
beamformers are applied to the non-calibrated microphone
signals. We will substantiate, by means of computer simulations,
that the proposed approach gives identical results compared
to the setup where microphone signals are first calibrated, so
that clock-offset compensation and microphone gain equalisation
becomes unnecessary.
Index Terms—Beamforming, clock synchronisation, microphone
gain equalisation, wireless acoustic sensor networks