The audio file begins with everyday sounds — birds chirping, a child screaming, a dog barking. You can hear them flying by a couple of times and even hear the wings flapping. “You hear more distant sounds you normally wouldn’t hear, including distant birds and other types of activities,” he said. Others still might adjust their frequency, going to a higher pitch to cut through urban noise. “You could hear all these crazy frequencies from ventilation shafts and vending machines, sounds that normally are not easily perceived.

Source: thestar April 18, 2020 11:07 UTC