In a technique for canceling noise from a microphone communications path,
an electrical equivalence circuit which is positioned close to and
electrically matched to the microphone produces a signal free reference
signal. The microphone converts speech to a voice signal. An analog
multiplexer alternately switches from the microphone to the electrical
equivalence circuit to produce a multiplexed analog signal composed of the
voice signal from the microphone and the signal free reference signal from
the electrical equivalence circuit. A wire connects the output of the
analog multiplexer switch to an A/D converter. The wire picks up noise
from the surrounding environment. The A/D converter converts the
multiplexed signal having the noise to a plurality of voice samples taken
from the voice signal portion of the multiplexed signal and a plurality of
noise samples taken from the signal free reference signal portion of the
multiplexed signal. A noise cancellation unit applies a noise suppression
algorithm (e.g., spectral subtraction) to the plurality of noise samples
and the plurality of voice samples to reproduce the voice signal with the
noise suppressed.