Hypersensitivity in an acoustic context describes an increased perception of volume, in which even normal everyday noises are experienced as unpleasant or painful. It can be a consequence of hyperacusis, but can also occur temporarily after exposure to noise or stress-related central modifications. Diagnostically, discomfort thresholds (UCL) are determined to quantify the degree of hypersensitivity. Therapeutic approaches include gradual desensitization with controlled noise stimuli and cognitive behavioral therapy to reduce emotional distress. In hearing aid fitting, compression is carefully adjusted so as not to exacerbate hypersensitivity.

A conductive hearing disorder refers to any functional impairment in which sound does not reach the inner ear efficiently through air conduction or bone conduction. Causes include cerumen impaction, tympanic membrane perforations, or ossicular fixations such as otosclerosis. Clinically, this manifests as a spread between normal bone conduction thresholds and elevated air conduction thresholds on the audiogram. Treatment depends on the cause: surgical reconstruction, removal of obstacles, or use of bone conduction hearing systems. Regular tympanometry and otoscopy monitor the success of the therapy.

Auditory adaptation is the decrease in volume perception during continuous or repeated sound stimulation in order to protect the auditory system from permanent overstimulation. It manifests itself as an increase in the hearing threshold for continuous tones or noise over time. Adaptation mechanisms occur in hair cells, cochlear synapses, and central auditory pathways. In hearing aid technology, adaptive compression algorithms are being developed that mimic these natural processes in order to maintain sound consistency. Lack of or delayed adaptation can lead to fatigue and discomfort.

Auditory fatigue refers to the temporary reduction in loudness perception and hearing acuity after prolonged exposure to sound, especially at high levels. It manifests itself in increased hearing thresholds and reduced discrimination ability, which recover after periods of rest. The mechanisms involved are hair cell fatigue, synaptic exhaustion, and central adaptation processes. Audiologically, fatigue is quantified with tests before and after noise exposure in order to determine risk limits for hearing protection. Rehabilitation through staggered listening breaks and programmed "recovery noise" supports regeneration.

Auditory filtering describes the ability of the ear to separate relevant sound components (e.g., speech) from background noise based on frequency, time, and spatial cues. In the cochlea, basilar membrane, receptor, and neural filters emphasize or attenuate certain frequency bands. Central filtering mechanisms in the auditory pathway and cortex select signals according to meaning and context. In hearing aids, this is technically replicated by multiband filters, noise reduction, and directional microphones. Efficient filtering improves speech comprehension in noisy environments and reduces cognitive load.

Auditory localization is the ability to determine the direction and distance of a sound source. It is based on interaural time differences (ITD) and interaural level differences (ILD), as well as spectral filter effects of the outer ear and head-body transfer functions. Central processing centers in the brainstem (olive complex) combine these cues to enable spatial hearing. Damage to binaural signal processing leads to localization limitations and reduced situational awareness. Hearing systems with binaural networking support natural localization by maintaining cues synchronously.

Auditory masking describes the phenomenon whereby loud sounds mask quiet sounds of the same or similar frequencies, preventing them from being heard. This creates critical bands within the ear where masking energy is particularly effective. Masking is used as a diagnostic tool in audiometry and in hearing aids for tinnitus masking or noise suppression. Adaptive masking filters take individual critical bandwidths into account for effective noise suppression. Psychoacoustic masking effects are fundamental to compression and noise management algorithms.

Auditory plasticity is the ability of the auditory system to adapt structurally and functionally to changes in acoustic stimuli or hearing loss. It includes the formation of new synapses, cortical reorganization, and changes in auditory pathway connections. Plasticity enables recovery after sudden hearing loss, adaptation to hearing aids and cochlear implants, and the learning of new hearing strategies. Rehabilitation training and musical listening promote plastic processes and improve speech comprehension and sound perception. Plasticity decreases with age, which is why early intervention is recommended.

The auditory threshold is the minimum audible sound pressure level for a stimulus at a given frequency and duration. It is documented in the audiogram as the hearing threshold for tones (dB HL) and forms the basis for diagnosing hearing loss. Shifts in the threshold of more than 20 dB from the norm indicate hearing impairment. Different types of thresholds—absolute, terminal, and discomfort thresholds—characterize the entire dynamic hearing experience. Repeated threshold measurements enable progress monitoring during therapy or noise protection measures.

Auditory processing encompasses all central neural mechanisms that transform and interpret acoustic signals from the cochlea to the cortex. It includes temporal and spectral analysis, pattern recognition, and speech comprehension. Disorders of processing—such as central auditory processing disorders—lead to comprehension difficulties despite normal peripheral function. Diagnostic procedures such as evoked potentials and dichotic tests examine the processing levels. Rehabilitation through auditory training uses plastic adaptation to strengthen deficient processing components.

Auditory perception refers to the conscious experience of sound characteristics such as volume, pitch, timbre, and spatial location. It arises through the integration of peripheral stimuli and cognitive processes in the auditory cortex and associated areas. Perceptual phenomena such as gestalt formation (auditory scene analysis) and attention control determine which sound sources are in focus. Perception is measured psychophysically using threshold and discrimination tests. Impairments occur in cases of tinnitus, hidden hearing loss, or central disorders and require targeted training.

Ultrasonic frequencies are sound frequencies above the human hearing range (>20 kHz). Although not consciously audible, they can cause resonances and nonlinear effects in the outer and inner ear acoustics. In otoacoustics, ultra-high frequency emissions (up to 100 kHz) are used to test outer hair cell functions with high resolution. Ultrasound in the hearing range is used in medicine (Doppler sonography) and materials testing, but not for conventional hearing tests. Research is investigating the possible biological effects of ultra-high frequencies in hearing aids and ambient noise.

Ambient noise refers to all acoustic signals in the environment that are not part of the target stimulus, such as traffic noise, conversations, or machine noise. These signals affect speech comprehension, listener fatigue, and the performance of hearing aids. Audiologists measure signal-to-noise ratios (SNR) in typical everyday situations in order to optimize treatment concepts. Noise reduction algorithms and directional microphones in hearing aids reduce disruptive ambient noise. In room planning, noise maps and acoustic simulations are used to control ambient noise levels.

The uncomfortable level (UCL) is the sound pressure level at which a sound is perceived as unpleasant or painful. It is typically 80–100 dB HL above the hearing threshold and varies individually with frequency and hearing status. UCL measurements are important for setting the maximum output power of hearing aids to avoid overamplification. Deviations may indicate hyperacusis or central auditory dysregulation. Follow-up checks of the UCL help to adjust comfort parameters to the situation.

The just-noticeable difference (JND) is the smallest perceptible difference in an acoustic stimulus, e.g., in volume or frequency. It is determined using methods such as the double comparison method and is frequency- and level-dependent. Typical loudness JNDs are around 1 dB, while frequency JNDs are 0.2–1% of the carrier frequency. In hearing aids, JND values are used in the fine tuning of compression and filter bandwidths. Increased JNDs indicate reduced resolution and can explain speech comprehension problems.