Systems and techniques relating to interpreting signals on a noisy channel
with polarity uncertainty. A signal processor, such as a read channel
transceiver device usable in a magnetic recording system, includes a
detector operable to find a data pattern that indicates control
information in a read signal and to determine a signal polarity of the
read signal by determining Euclidean distances between a sampled sequence
from the read signal and multiple possible sequences corresponding to
preamble-shifted and polarity-reversed versions of the data pattern. The
read signal is obtained from a partial response channel, such as in a
storage device, and the data pattern can be a servo mark selected based
on Euclidean distances between the servo mark and preamble-shifted and
polarity-reversed versions of the servo mark generated according to a
target channel and an encoding scheme specified for the storage medium.