There's often talk in the field of EVP research about capturing voices that are outside the human hearing range, but this is not something that is easily done. It requires specialized equipment and is impractical as part of a paranormal investigation.

The human hearing range, or audible range, is the frequency range that the human ear can detect. The cochlea in the ear is only stimulated by a limited range of frequencies. This means that we can only hear certain frequencies. The range of normal human hearing is 20 to 20,000 Hz.

If a voice were outside of this range, it would be speaking at a pitch so low that we can't imagine how that would even sound. On the other hand, if a voice is at a frequency higher than the human audible range, then it would be beyond any piercing high-pitch sound we've ever heard.

There are many cases where an...