Very low-frequency sounds are called infrasound. They have a frequency ranging from 0.1 to 20 Hz. These sounds are below the human range of hearing. While infrasound isn't commonly linked to EVPs, how these sounds affect us is a common area of research for parapsychologists because these low-frequency vibrations have been known to cause people to report discomfort in the form of disorientation, feeling panicked, and an increased heart rate and blood pressure. In extreme cases, infrasound has been attributed to feelings of depression, a general feeling of unease, as well as visions of apparitions.

Scientists researching the low-frequency noise created by wind turbines and traffic noise discovered the effects of infrasound on humans. They found a link between infrasound and the sensations often described as getting chills down the spine.

As specialist audio equipment is required to detect infrasound, it can be hard to eliminate this from your investigation. However, keeping...