Hz

Infrasonic waves have a frequency of less than 20Hz.

The tuning note A4 is equal to 440 Hz.

At the other end of the spectrum are very low-frequency sounds (below 20 Hz), known as infrasound.

Bats can hear at among the highest frequencies of any mammal, up to 120,000 Hz. They use ultrasonic vocalizations as sonar, allowing them to pursue tiny insects in the dark without bumping into objects.

When your dog tilts his head to listen to seemingly imaginary sounds, he is tuning in to ultrasonic frequencies, as high as 45,000 Hz.