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A Hole in the Water

The practice of "deplatforming" individuals on the basis of content is actually just another form of signal filtering with all the advantages and disadvantages that go with it.  "Filtering is a class of signal processing, the defining feature of filters being the complete or partial suppression of some aspect of the signal".  Recently the New York Times sat in as Twitter attempted to formulate a set of rules determining what signals would be allowed to pass.

On Friday, to provide more transparency about its decision making, Twitter invited two New York Times reporters to attend the policy meeting. During the one-hour gathering, a picture emerged of a 12-year-old company still struggling to keep up with the complicated demands of being an open and neutral communications platform that brings together world leaders, celebrities, journalists, political activists and conspiracy theorists.

Even settling on a definition of dehumanizing speech was not easy. By the meeting’s end, Mr. Dorsey and his executives had agreed to draft a policy about dehumanizing speech and open it to the public for their comments.

To Twitter's credit they realized the process was hard. After all, if filters are erroneously defined they will become a liability.  Not only will they  block out irrelevant information but the crucial signals as well.  If an adversary knows the filter, he can mimic what the system is programmed to ignore and become invisible -- a "black hole in the water" to use a naval metaphor.

For this reason critical detection systems are often combinations of relatively unmediated input and much more heavily filtered displays.  "In a passive sonar system ... sources fall into two main categories: broadband and narrowband ." The former listens to everything, including unknown signals, while the latter focuses on known signal types.

Broadband sources, as the name suggests, [is from] acoustic energy over a wide range of frequencies.... Narrowband sources radiate within a small band about a particular frequencies [of] the various pieces of machinery found in every ship. For example, pumps, motors, electrical generation equipment and propulsion systems. When specifying narrowband sources, it is important to also specify the frequency at which it occurs.

A Navy article describes how this works in practice; sonar teams have someone assigned to scan for any noise and if it looks interesting then drill down with a narrowband filter to bring out its signature.

"The broadband operator's job is eyes on the screen, head phones on, and constantly search 360 degrees around the ship," Whitson said. "He doesn't stop. If he hears something, he will put a tracker on it so we can send the data to the control room."

Whitson gave a brief description of the broadband noise. "The background noise of the ocean sounds like white noise," he said. "Imagine turning the lights off, turning the air conditioner down to about 60 degrees, and staring at a screen with green and black lines."

STSs are trained to pinpoint a variety of sounds over broadband noise. Often, they have to distinguish between animal, environmental, and mechanical noises. Their training requires the STSs to review publications based on history, which provides them with recorded data. Based on the data, STSs are given the knowledge to distinguish sounds.

"We listen to the sounds," Hudgins said. "When we hear those mechanical sounds, we use formulas that we can look up. We use sound, speed in water, and time difference."