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NPR has a story about Mosquito,  a high frequency outdoor generator being used by some 30 cities to discourage teenagers from staying in parks at night. According to the manufacturer's website, Mosquito generates an 18 kHz signal -- at that frequency, presumably a sine (because where would the harmonics live?) -- with an AGC to keep it 5 dB above ambient. No indication whether their AGC looks at broadband or just 18 kHz... but if it's broadband, then the noise is going to be a lot more obvious up there than +5 dB would suggest.

 

According to NPR, "anyone over age 25 is supposed to be immune because, basically, their ear cells have started to die off."

 

Later in the article: "In 2008, the United Nations Committee on the Rights of the Child implored the United Kingdom 'reconsider ... the Mosquito devices insofar as they may violate the rights of children.'

 

No mention of whether it discriminates against golden-eared audiophiles. 

 

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About fifteen years ago, NPR had a story about a similar device being used in shopping malls to move the kids along... with an on-air sample. AFAIK NPR back then was distributing its news on a 32kHz s/r channel.

They also had a downloadable sample so you could listen on better speakers. I remember checking it out: it was low bit mp3 encoded with a 22 kHz s/r. 

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It's so outrageous that it is funny.  I think a wrist-rocket and some steel ball bearings in steady hands would put an end to that stuff quickly.  Make them replace the stuff twice a week for a month or two and it will magically go away.

 

D.

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West Palm Beach, FL, has figured out how to use sound for social control (NYT) without relying on HF loss:

Baby Sharks

 

They play the repetitive (^3) children’s song in a loop all night to to keep homeless from sleeping on the grounds of a city-owned pavilion. 

 

No comments from people who live near the pavilion. Perhaps their kids are happy. 

 

—-

I lived in WPB for a few years. I don’t recall us even having sharks in the water while I was there. 

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