The Sheffield techno duo of Mark Bell and Gez Varley have a reputation that, at first glance, might seem to exceed their abilities. Having released only two records and not many more singles while they worked together, the pair's apparently meager contribution would hardly seem to bear out the claim that they were one of British techno's most important, agenda-setting groups. Nonetheless, early singles such as "We Are Back," "Freeze," and "Love Is the Message" from their debut Frequencies, as well as "Tied Up" from their second disc, Advance, have indelibly marked British tech...