A tracking apparatus identifies distorted output signals from a digital
system caused by at least one distorted signal input to the digital
system. A first signal is input to the tracking apparatus when a
distorted signal is input to the digital system. A second signal is input
to the tracking apparatus when a non-distorted signal is input to the
digital system. The tracking apparatus models a delay and widening
characteristics of the digital system and operates in parallel with the
digital system.