inaudible

Inaudible is an adjective used to describe sound that cannot be heard by the human ear. It can refer to sounds outside the human hearing range—either below the lower limit (infrasonic) or above the upper limit (ultrasonic)—as well as to sounds that are not perceived in a given listening situation.

The typical adult human hearing range runs roughly from 20 Hz to 20 kHz, though exact limits vary with age and individual factors. Sounds below about 20 Hz or above about 20 kHz are generally inaudible to humans. Infrasonic and ultrasonic sounds are common in nature and technology and may be detected by other animals or by specialized devices, but not by common human listeners.

In practical use, inaudible can describe sounds that are present but not perceived due to distance, masking by louder sounds, or poor transmission. In acoustics and audio engineering, inaudible content can be removed or encoded away in perceptual coding because it does not affect listeners; this is a key concept in reducing data without degrading perceived quality. In medical and industrial contexts, ultrasound (frequencies above 20 kHz) and infrasound are used for imaging and monitoring, though they are not audible to humans.

In everyday language, people may note that a whisper or distant noise is inaudible, meaning it cannot be heard in the given circumstances. The term is often contrasted with audible, which simply means capable of being heard.

Origin: from Latin inaudibilis meaning not to be heard, formed from in- (not) + audibilis (able to be heard).