The caloric test examines the function of the horizontal semicircular canal by introducing warm or cold water or air into the ear canal. Temperature differences generate endolymphatic currents that trigger typical nystagmus (rapid eye movements). The intensity and direction of the nystagmus provide information about vestibular functional asymmetries and central vestibular integrity. It is standard in the diagnosis of vertigo and helps to localize vestibular deficits on one side. Since the stimulation can be unpleasant, the examination is performed under continuous monitoring of eye movements.

Canal audiometry measures the sound conduction properties of individual frequency bands ("channels") in the ear canal or hearing aid. It uses narrow filter bands to determine thresholds and amplification requirements separately for each channel. The results help to precisely adjust multiband compression parameters and ensure clear speech comprehension. In research, channel audiometry is used to investigate frequency selectivity and masking effects. Modern hearing aid fitting software visualizes channel audiograms in real time for fine calibration.

A channel compressor is a dynamic processor that controls level compression separately in each frequency channel of a hearing aid. It reduces loud signals above the comfort threshold more than quiet signals in order to adapt the dynamic range to the residual hearing. Parameters such as ratio, attack and release times are optimized individually for each channel. Multi-channel compression makes it possible to emphasize speech components in critical bands while attenuating impulse-like noises. However, incorrectly adjusted compressors can cause sound artifacts and discomfort.

Channel separation refers to the division of the audio spectrum into separate frequency bands for independent processing. It forms the basis for multiband compression, filtering, and noise reduction in hearing aids. Good channel separation minimizes crosstalk between adjacent bands and prevents phase problems. The number and bandwidth of the channels are adjusted to the hearing loss profile and the processing power of the processor. Adaptive systems change channel boundaries depending on the situation to ensure optimal sound quality in changing environments.

The number of channels indicates how many frequency bands a hearing aid divides the audio signal into. Typical values range from 4 to 16 channels; more channels allow for finer adjustment but require higher processing power. A higher channel count supports precise masking management and individual amplification profiles. However, too many channels can lead to over-adjustment and increased noise. The ideal channel count depends on the hearing loss pattern and the processing capabilities of the wearer.

Capsulitis is an inflammation of the bony capsule of the inner ear, usually resulting from otitis media or a skull base injury. It causes severe ear pain, dizziness, and often sensorineural hearing loss. CT/MRI scans and laboratory tests are used to determine the extent of the inflammation and identify the pathogen. Treatment includes systemic antibiotics, pain management, and surgical drainage if necessary. Early treatment is essential to prevent permanent damage to the inner ear.

Cascade amplification refers to a multi-stage amplification architecture in which several amplifier stages are connected in series. Each stage increases the level slightly, achieving overall amplification without significant distortion. This technique improves noise performance and linearization compared to single stages with high amplification. In digital hearing aids, cascade amplification is found in both analog-to-digital converters and output amplifiers. It contributes to low inherent noise and high fidelity.

Sound compression reduces the dynamics of audio signals by attenuating loud sections more than quiet ones. In hearing aids, it is essential for protecting residual hearing from overloading while making weak signals audible. Compression parameters such as ratio, knee point, and release time determine the response behavior. Adaptive compression automatically adjusts to speech and ambient noise. However, incorrectly set compression can make the sound seem "flat" or unnatural.

The cerebellopontine angle is the anatomical space between the cerebellum and the pons through which the VIII cranial nerve passes. Acoustic neuromas, benign tumors that cause hearing loss, tinnitus, and vertigo, often develop here. Microsurgical resection requires access through this angle, whereby the brain stem and vessels must be spared. Intraoperative monitoring of the auditory brainstem exits protects nerve function. Postoperative imaging checks the completeness of the resection and for complications.

Der Klirrfaktor gibt das Verhältnis der Summe aller harmonischen Obertöne zur Grundschwingung an und quantifiziert Verzerrungen in einem System. In Hörgeräten beschreibt er, wie stark das Ausgangssignal vom Eingangssignal abweicht. Niedrige Klirrfaktoren (<1 %) sind wünschenswert für unverfälschten Klang. Messungen erfolgen mit Sinus‑Sweeps und Spektralanalyse. Hoher Klirrfaktor kann Sprachverständnis und Klangqualität erheblich verschlechtern.

Acoustic trauma is caused by extremely short, high-intensity sound explosions that can immediately destroy hair cells and synaptic connections in the inner ear. Symptoms include sudden hearing loss, tinnitus, and dizziness. Emergency treatment with high-dose corticosteroids and hyperbaric oxygenation can reduce damage, but must be administered immediately. Long-term consequences include permanent hearing loss and psychological stress. Prevention through hearing protection during gunfire or explosions is essential.

Bone conduction transmits sound directly to the cochlea via vibrations in the skull, bypassing the outer and middle ear. It is used in audiometry to distinguish between conductive and sensorineural hearing loss. Bone conduction hearing aids are used to treat patients with middle ear problems. Implantable bone conduction devices (BAHS, Bonebridge) deliver higher sound quality than traditional bone conduction headphones. Bone conduction also plays a role in autophony.

The cochlea is the snail-shaped organ in the inner ear where sound waves are converted into electrical nerve impulses. The basilar membrane is lined with inner and outer hair cells, which encode sounds of different frequencies through mechano-electrical transduction. Tonotopy ensures that high frequencies are detected at the base and low frequencies at the apex of the cochlea. Damage to the cochlea, for example due to noise or ototoxins, leads to permanent sensorineural hearing loss. Research into cell regeneration and cochlear implants aims to restore function.

Communicative accessibility means that people with hearing loss have unrestricted access to linguistic content, for example through sign language, subtitles, inductive hearing systems, or real-time transcription. It encompasses technical, architectural, and organizational measures in public spaces, media, and digital offerings. The goal is equal participation in education, culture, and everyday life. Legal requirements mandate accessibility in public institutions and online services. Audiologists and hearing care professionals advise on suitable aids and installations.

Compensation methods are used to compensate for hearing loss through technical or therapeutic means. They range from hearing aids and implants to auditory training and environmental adjustments. Digital signal processors use multiband compression, noise reduction, and directional microphones to amplify speech components. Therapeutic compensation includes central auditory processing training to promote neural plasticity. A combination of technical and rehabilitative compensation achieves the best results for speech comprehension.

Compression dynamics describe how a hearing aid responds to different input levels: quiet signals are amplified more than loud ones in order to make optimal use of the wearer's dynamic range. Important parameters include compression ratio, knee point, and attack/release time. A fast attack time protects against impulse noise, while a slow release time preserves natural sound transitions. Individual fine-tuning adapts the dynamics to the hearing loss profile and hearing preferences. Mismatches can impair speech comprehension and sound quality.

In conductive hearing loss, sound transmission through the outer ear or middle ear is impaired, for example due to cerumen impaction, tympanic membrane perforation, or otosclerosis. Those affected have normal bone conduction but elevated air conduction thresholds on the audiogram. Treatment options include surgical reconstruction, removal of obstructions, or bone conduction hearing aids. Tympanometry and the Rinne test help to distinguish between conductive and sensorineural hearing loss. The prognosis is usually very good if treatment is successful.

The head-related transfer function (HRTF) describes how the head, ears, and torso filter sound depending on frequency, thereby generating directional cues. It is essential for spatial hearing and virtual reality audio. Individual HRTFs are recorded with microphones at the ear or calculated to produce realistic 3D audio effects. In hearing aid development, HRTF models are used to maintain natural localization despite the device. Adaptive algorithms can adjust HRTFs to head movements in real time.

Headphones are sound transducers that are positioned directly on the ear and transmit sound to the eardrum in an isolated manner. They are used in audiometry (everyday testing and research) and as accessories for hearing aid streamers. Closed designs offer high shielding against ambient noise, while open designs provide a more natural sound. Calibrated measurement headphones ensure standardized sound levels during threshold tests. Hygiene and comfort are important for accurate and reliable measurements.

The force law of hair cells describes the nonlinear relationship between the deflection of hair cell stereocilia and the electrical response triggered. Small deflections lead to proportionally larger receptor potentials, which explains the sensitivity of the cochlear amplifier. When certain deflection limits are exceeded, the characteristic curve flattens out to provide protection against overstimulation. Changes to this law due to damage affect the dynamic range and frequency resolution. Biophysical models help to optimize hearing aid compression.

A crystal calibrator generates a defined sound pressure level (usually 94 dB SPL at 1 kHz) in a closed adapter to test microphone sensitivities. It uses piezoelectric crystals for stable frequency and amplitude. Calibration before each measurement ensures accuracy in audiometry and room acoustics. Regular traceability to national standards ensures measurement consistency. Documentation of calibration is part of quality control in laboratories and clinics.

Auditory short-term memory stores acoustic information for seconds to minutes in order to process speech and sounds. It enables the understanding of sentences by retaining previous words in memory. Impairments lead to difficulties with longer passages of speech and complex listening situations. Tests such as dichotic number span measure auditory memory performance. Auditory training and cognitive exercises can improve short-term memory functions.