inaudibility

Inaudibility refers to the state in which sound cannot be perceived by a listener under specific conditions. In psychoacoustics, audibility is defined relative to the listener's threshold of hearing, which depends on frequency, amplitude, background noise, and the listener's own hearing ability.

Common causes include low sound pressure level (amplitude) due to distance or attenuation, high ambient noise levels that mask the signal, atmospheric absorption and air humidity, and spectral masking where one sound masks another. Sounds outside the typical human hearing range (roughly 20 Hz to 20 kHz) are generally inaudible to humans regardless of level. Hearing impairment or cochlear damage can raise the threshold of audibility.

Audibility is often represented by psychoacoustic models and audibility curves, such as the equal-loudness contours. A sound may be audible at a given level for some listeners but inaudible for others; loudness, masking, and temporal factors influence perception. In digital audio, inaudibility is also leveraged via perceptual coding, removing information that falls below the audible threshold.

In design and communication, inaudibility is considered in room acoustics, indexing, and signal transmission. For instance, designers aim to keep speech above the hearing threshold while reducing noise, and audio codecs encode only components that are perceptually significant.