One of the designers, Peter van Hengel explained to me that the idea grew out of a project at the University of Groningen, which simulated the workings of the inner ear with computer models. "A colleague of mine applied the same inner-ear model to trying to recognize speech amid noise," he said, "and found that it could be used to select the parts belonging to the speech and leave out the noise." They founded Sound Intelligence in 2000, initially focussing on speech-noise separation for automatic speech recognition, with a sideline in the analysis of non-speech sounds. In 2003, the company was approached by the Dutch national railroad, which wanted to be able to detect several kinds of sound that might indicate trouble in stations and on trains (glass-breaking, graffiti-spraying, and aggressive voices). This project developed into an aggression-detection system based on the sound of people shouting: the machine detects the overstressing of the vocal cords, which occurs only in real aggression. (That’s one reason actors only approximate anger; the real thing can damage the voice.)

The city of Groningen has installed an aggression-detector at a busy intersection in an area full of pubs. Elevated microphones spaced thirty metres apart run along both sides of the street, joining an existing network of cameras. These connect to a computer at the police station in Groningen. If the system hears certain sound patterns that correspond with aggression, it sends an alert to the police station, where the police can assess the situation by examining closed-circuit monitors: if necessary, officers are dispatched to the scene. This is no Hal, either, but the system is promising, because it does not pretend to be more intelligent than it is. I thought the problem with the technology would be false positives: too many loud noises that the machine mistook for aggression. But in Groningen, at least, the problem has been just the opposite. "Groningen is the safest city in Holland," van Hengel said, ruefully."There is virtually no crime. We don’t have enough aggression to train the system properly."

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Source: The New Yorker, 23 June 2008 (by John Seabrook)