Otto Julius Zobel (October 20, 1887 – January 1970) was an electrical engineer who worked for the American Telephone & Telegraph Company (AT&T) in the early part of the 20th century.

[6][7] He was the son of Oscar Ewald "Herman" Zobel, who had emigrated to the United States from his native Germany in 1860, and his wife Ernestine, née Kahl.

Zobel stayed at the University of Wisconsin as a physics instructor from 1910 to 1915, and graduated with his PhD in 1914;[6] his dissertation concerned "Thermal Conduction and Radiation".

[6] The last of Zobel's prolific list of patents[16][17] occurred for Bell Labs in the 1950s, by which time he was residing in Morristown, New Jersey.

[24] Ingersoll and Zobel state that in many cases the calculation involved makes the solution "well-nigh impossible" by analytical means.

As the idea was to put another (completely different) signal in the slot vacated by the unwanted sideband it was important that all traces of it were removed to prevent crosstalk.

This standard in telephony is still in use today and had remained widespread until it began to be supplanted by digital techniques from the 1980s onwards.

Sharper cut-offs and higher stopband rejection to any arbitrary design specification could be achieved merely by increasing the length of the ladder.

[30] After Zobel arrived at the Engineering Department of AT&T he used his mathematical skills to further improve the design of electric wave filters.

A fast transition between passband and stopband was one of the primary requirements for cramming as many telephone channels as possible into one cable.

[2][32] One disadvantage of the m-type section was that at frequencies past the pole of attenuation, the response of the filter started to increase again, reaching a peak somewhere in the stopband and then falling again.

[33] Zobel overcame this problem by designing hybrid filters using a mixture of constant k and m-type sections.

Zobel found that a value of m = 0.6[36][37] for the end half sections, while not mathematically exact, gave a good match to resistive terminations in the passband.

These "image" impedances have a mathematical characterization impossible to construct simply out of discrete components, and can only ever be approximated.

Zobel found that using these impedances constructed out of small filter chains as components in a greater network allowed him to build realistic line simulators.

These were not in any sense intended as practical filters in the field, but rather the intention was to construct good controllable line simulators without having the inconvenience of miles of cable to contend with.

[43] Zobel invented several filters whose defining characteristic was a constant resistance as the input impedance.

With modern computing power, a brute force approach is possible and easy—that is, simply incrementally adjusting each component while recalculating in an iterative process until the desired response is achieved.

During World War II he moved on to waveguide filters for use in the newly developed radar technology.

[48] Little was published during the war for obvious reasons but towards the end with Bell Labs in the 1950s, Zobel designs for sections to match physically different waveguide sizes appear.

[46] While Carson led the way theoretically, Zobel was involved in the design of filters for the purpose of noise reduction on transmission systems.

The line of attack against noise from the radio engineers included developing directional antennae and moving to higher frequencies where the problem was known not to be so severe.

[52][53] The radio engineers' preoccupation with static and the techniques being used to reduce it led to the idea that noise could be eliminated by, in some way, compensating for it or canceling it out.

[55] Armstrong was technically in the wrong in this exchange, but in 1933, ironically and paradoxically, went on to invent wideband FM, which enormously improved the noise performance of radio by increasing the bandwidth.

[5] Although this work by Carson and Zobel was very early, it was not universally accepted that noise could be analyzed in the frequency domain in this way.

[57] This work on noise produced the concept, and led Zobel to pursue the design, of matched filters.

The purpose of this research is to attempt to demonstrate that the results obtained from genetic programming are comparable to human achievements.

This was judged to be human-comparable, not only because of the patent, but also because the high-pass and low-pass sections were "decomposed" as in Zobel's design, but not specifically required to be so in the programs parameters.