High Quality Content by WIKIPEDIA articles! Otto Julius Zobel (October 20, 1887 – January 1970) was a design engineer who worked for the American Telephone Telegraph Company (AT T) in the early part of the 20th century. Zobel`s work on filter design was revolutionary and led, in conjunction with the work of John R. Carson, to significant commercial advances for AT T in the field of frequency division multiplex (FDM) telephone transmissions.