The latter refers to the very low-frequency sounds male elephants issue during their annual period of heightened sexual activity.

Many residents say they believe the hum is a low-frequency sound created unintentionally by industrial equipment, though its source has not been pinpointed.

"The thing about low-frequency sound is that it can go for miles," he said.

"The idea is that these low-frequency sounds were important in religious rituals for changing states of consciousness," he said.

"I think low-frequency sound, when played above a certain volume, is very conducive to a meditative state or a trance," Anderson said.

But someone whose hearing is impaired generally needs high-frequency sounds amplified more than low-frequency sounds.

The film uses extremely low-frequency sound during the opening scenes to create a state of disorientation and unease in the audience.

Like other whales, males make long, loud, low-frequency sounds.

This species often approaches ships, as they are attracted to certain artificial, low-frequency sounds.

The sei whale makes long, loud, low-frequency sounds.