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Engineers in South Korea have created a computer filter that can listen to a half-second of audio and determine whether or not it's pornography. It seems porn has a distinct set of audio characteristics, and here we'll just sit back and let New Scientist explain:

Speech signals are normally low-pitched and musical clips have a wide range of pitches; both vary only gradually over time. In contrast, pornographic sounds tend to be higher-pitched, change quickly and also periodically repeat.

Got that? High-pitched and repetitive = porn. (Make all the pop music jokes you like in the comments section, guys.)

Anyway, the program's not foolproof--it can be thrown off if the porn uses background music, and sometimes it also mistakes "comedy shows with laughter" for X-rated material. (New Scientist: "The loud audience cheers and cries share similar spectral characteristics to sexual sounds.") But the program was able to separate porn from non-porn, including "music, movies, news, and sport," with 93 percent accuracy.

Until now, most porn filters have worked on a visual basis, flagging clips that show a lot of skin. But as you might imagine, this system isn't perfect. The researchers behind the audio filter believe it has the potential to be a lot more effective. And Geek.com points out that there are any number of businesses who might be interested in technology like this: "A great example of that is YouTube as it needs to keep its service free of porn, and anything classed as remotely adult sits behind an age warning."