A first set of signals from an array of one or more microphones, and a
second signal from a reference microphone are used to calibrate a set of
filter parameters such that the filter parameters minimize a difference
between the second signal and a beamformer output signal that is based on
the first set of signals. Once calibrated, the filter parameters are used
to form a beamformer output signal that is filtered using a non-linear
adaptive filter that is adapted based on portions of a signal that do not
contain speech, as determined by a speech detection sensor.