Dogs hear frequencies from 12 to 80,000 Hertz (or oscillations per second), and humans - from 16 to 20,000. The dog is able to differentiate up to 9,000 sounds of different heights and feel the strength of the sound from 0.1 to 120 decibels. Dogs hear sounds of medium strength at a distance of 40-50 m (humans - 6-10 m). Hearing aids when turned on emit a high-frequency sound that people don't hear. And when their microphones are too close to each other, loud feedback sounds arise that attract dogs.