How you hear
The sound that you hear is the vibration of the air pressure that hits your eardrum. The air pressure vibrates from below atmospheric pressure to above atmospheric pressure. The frequency at which the pressure vibrates is measured in Hertz (Hz). The outer limits of young humans is about 20 Hz to 20K Hz (20,000 Hz). I say young humans because your hearing degrades as you get older. The average middle-aged person doesn’t hear anything much higher than 16KHz.
How dogs hear
Dogs have a much higher range of hearing. Dogs can hear from about 64Hz to about 65Khz when they are young. As in humans, dog’s hearing also degrades as they get older. The average dog whistle frequencies range from 16Khz to 22KHz.That’s why, at least at the higher frequencies, most people can’t hear them.
The shape of a dog’s ears doesn’t affect the frequency that the dog can hear, but does affect the acuteness or sensitivity of the dog’s hearing. Dogs with flaps over their ears, like Bloodhounds, Basset Hounds and Poodles don’t hear as well as dogs with prick ears, ears that stand up straight, like those of German Shepherds or Pomeranians. Also, some dogs with prick ears can rotate them somewhat to get a better sense of where the sound is coming from.
In general, dogs can hear significantly better than humans, both in terms of frequency of the sound and the loudness of the sound. From about 65Hz to 3K Hz dogs have about the same hearing sensitivity as humans. For frequencies from 3K Hz to 12K Hz, dogs hearing becomes progressively more sensitive than that of humans. Beyond 12K Hz, dog’s hearing is so much more sensitive than human’s that there is really no comparison. That’s one of the reasons that a lot of dogs try to get away from vacuum cleaners. It’s not that they are afraid of them. It’s because they produce sounds that are so loud that they hurt the dog’s ears, but are so high in frequency that the human running the vacuum cleaner doesn’t hear them.
There may be situations when your walking your dog, and your dog stops and listens or looks at something. You look in the direction your dog is looking and you don’t see or hear anything unusual. It’s probably because your dog heard a sound that is too faint or too high in frequency for you to hear and looks to see where the sound is coming from. It happens to me frequently when I walk my greyhound in the evening.