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Auditory masking

Auditory masking is the psychoacoustic phenomenon in which the presence of one sound, known as the masker, elevates the detection threshold of another sound, called the signal or target, thereby impairing its perception.^[1] This effect arises from the auditory system's limited capacity to process multiple sounds simultaneously and is a cornerstone of understanding human hearing.^[1] Masking is broadly categorized into energetic and informational types. Energetic masking occurs due to the spectral and temporal overlap of the masker and signal energies, primarily at the peripheral level of the auditory system, such as in the cochlea.^[2] In contrast, informational masking results from central auditory processing challenges, including perceptual uncertainty, similarity between sounds, or difficulty in segregating the target from the masker in complex acoustic scenes.^[2] Additionally, masking can be simultaneous, when the signal and masker coincide in time, or temporal, encompassing forward masking (where the masker precedes the signal by a short interval) and backward masking (where the masker follows the signal).^[1] Temporal masking effects typically decay within 100-200 milliseconds after the masker offset.^[1] Historically, auditory masking was first systematically studied in the early 20th century, with seminal experiments by Wegel and Lane demonstrating how one pure tone masks another based on frequency proximity.^[1] These investigations revealed the frequency-selective nature of auditory filters, modeled as bandpass filters with bandwidths of about 10-15% of their center frequency, as measured via methods like psychophysical tuning curves and notched-noise masking.^[1] In practical applications, auditory masking principles underpin perceptual audio coding schemes, such as those in MP3 compression, where inaudible components masked by louder sounds are discarded to reduce file sizes without compromising perceived quality.^[3] Similarly, in hearing aids, techniques like auditory masked threshold noise suppression exploit masking to enhance speech clarity by attenuating background noise that would otherwise obscure target sounds.^[4]

Fundamentals

Definition and Types

Auditory masking refers to the phenomenon in which the presence of a masker sound elevates the detection threshold of a target sound, rendering the target inaudible or more difficult to perceive.^[5] This occurs when the auditory system struggles to distinguish the target amid competing acoustic energy or perceptual complexity. The masked threshold represents the minimum intensity level at which the target sound becomes detectable in the presence of the masker.^[6] The systematic study of auditory masking began in the early 20th century with the work of Wegel and Lane, who in 1924 examined how one pure tone masks another and linked it to inner ear dynamics.^[6] This laid foundational insights into masking mechanisms. The concept was further formalized in psychoacoustics by Fletcher and Munson in 1937, who established key relationships between sound loudness and masking effects through experimental measurements.^[7] Auditory masking is primarily divided into energetic masking and informational masking. Energetic masking involves peripheral interference within the auditory periphery, particularly overlapping excitation patterns along the basilar membrane in the cochlea, where the masker's energy suppresses neural responses to the target.^[5] A representative example is broadband noise masking a faint pure tone in an otherwise quiet environment, as the noise overwhelms cochlear detection of the tone's frequency-specific vibrations.^[6] Informational masking, by contrast, arises from central auditory processing limitations, where perceptual uncertainty or similarity between the target and maskers overloads higher-level interpretation, even without significant energy overlap.^[8] This type was first articulated by Pollack in 1975 to describe masking beyond peripheral energetics.^[8] An illustrative case is the cocktail party scenario, where multiple simultaneous talkers in a crowded room hinder comprehension of a single speaker due to competing linguistic and attentional demands, despite individual words remaining acoustically detectable.^[8]

Masked Threshold

The masked threshold is defined as the minimum sound pressure level at which a target sound becomes detectable in the presence of a masking sound, representing the point where the target is just audible despite the interfering stimulus.^[9] This concept, first quantitatively explored in early psychophysical studies, quantifies how the masker elevates the detection threshold of the target compared to quiet conditions.^[6] Masked thresholds are typically measured using psychophysical procedures that minimize bias and ensure reliable estimates of detectability. Common methods include adaptive tracking paradigms, such as the two-interval forced-choice (2IFC) task, where listeners identify which of two intervals contains the target amid the masker, with stimulus levels adjusted dynamically to converge on the 70.7% correct performance point. These techniques, refined over decades, allow for efficient threshold estimation by focusing trials near the detection boundary and accounting for listener response variability. The extent of masking is often expressed as the threshold shift, calculated as

\text{threshold shift} = 10 \log_{10} \left( \frac{I_{\text{masked}}}{I_{\text{quiet}}} \right),

where I_{\text{masked}} is the intensity of the target at threshold with the masker present, and I_{\text{quiet}} is the intensity at the absolute threshold without masking; this yields the threshold shift in decibels (dB).^[10] For tonal maskers close in frequency to the target, typical shifts range from 10 to 20 dB, depending on the masker-target separation and overall stimulus levels.^[6] Several factors influence the masked threshold, including the overall level of the masker, which generally produces greater elevation as intensity increases due to enhanced peripheral excitation overlap.^[11] Target duration also plays a role, with shorter signals yielding higher thresholds because of limited temporal integration in the auditory system.^[12] Additionally, listener variability contributes to differences in masked thresholds, arising from individual differences in cochlear mechanics and attentional factors.^[13] Both energetic masking, from overlapping excitation patterns, and informational masking, from perceptual uncertainty, can contribute to this threshold elevation.^[9]

Simultaneous Masking

Critical Bandwidth

The critical bandwidth (CBW) represents the frequency range over which sounds interact most effectively in the auditory system, arising from the overlapping excitation patterns produced by those sounds on the basilar membrane. Within this bandwidth, a masker tone or noise elevates the detection threshold of a target sound more substantially than when the sounds are separated by larger frequency intervals, reflecting the limited frequency resolution of the cochlea's mechanical filtering. This concept underpins simultaneous masking, as energy from the masker spreads across the basilar membrane, interfering with the neural representation of nearby frequencies.^[14]^[15] In the 1960s, Eberhard Zwicker formalized the CBW in his model of auditory processing, defining it as the approximate width of an auditory filter centered at a given frequency, which aligns closely with the equivalent rectangular bandwidth (ERB) of these filters. Zwicker's framework subdivided the audible spectrum into 24 critical bands, each corresponding to regions of integrated auditory processing where loudness summation and masking effects occur nonlinearly. This model built on earlier psychophysical observations but provided a quantitative basis for understanding how the ear groups frequencies into perceptually equivalent units.^[14] The ERB, as a measure of filter bandwidth, is approximated by the formula

\text{ERB}(f) \approx 24.7 + 0.108f

where f is the center frequency in Hz; for instance, at a center frequency of 1 kHz, the ERB is approximately 132.7 Hz, indicating the span over which masking interactions are prominent. This linear approximation captures the filter's broadening with increasing frequency, mimicking the anatomical gradient along the basilar membrane. More refined polynomial forms exist, but this equation suffices for estimating bandwidths in the typical speech range of 100 Hz to 8 kHz. CBW values are empirically derived from masking experiments, in which the threshold shift for a target tone is measured as a function of its frequency separation from a masker; masking reaches its peak when the target and masker fall within the same CBW, beyond which the effect diminishes sharply. Zwicker employed techniques such as masking a narrowband noise with flanking tones to delineate these boundaries, confirming that CBW increases from about 100 Hz at low frequencies to over 3 kHz at high frequencies. These measurements validate the CBW as a functional equivalent to the auditory filter's passband, essential for modeling frequency selectivity without direct physiological access.^[14]

Frequency and Intensity Effects

In simultaneous auditory masking, the strength of masking depends critically on the frequency relationship between the masker and the target signal. When the masker and target frequencies are similar—termed on-frequency masking—the masking effect is strongest because the masker's energy is concentrated within the same auditory filter centered on the target's frequency. In contrast, masking weakens as the frequency separation increases, reflecting the auditory system's frequency selectivity, where dissimilar frequencies engage different filters with less overlap. This effect is asymmetric: a masker at a lower frequency than the target produces greater masking at higher frequencies—a phenomenon known as upward spread of masking—due to the broader spread of excitation toward higher frequencies along the basilar membrane. Conversely, downward spread from higher-frequency maskers to lower targets is more limited, resulting in weaker masking. The intensity of the masker also modulates masking strength in a non-linear fashion. Near the critical band, the masked threshold typically shifts by approximately 3 dB for every 10 dB increase in masker intensity, indicating compressive processing that tempers the growth of masking compared to a linear expectation. At low intensities close to threshold, masking follows a more linear pattern, but as masker levels rise, cochlear compression reduces the relative impact, leading to shallower slopes in the growth-of-masking function—often around 0.3 to 0.5 for off-frequency maskers. This non-linearity arises from the active amplification and saturation mechanisms in the cochlea, which alter the effective excitation patterns at higher levels. Listeners can mitigate masking through off-frequency listening, where they attend to spectral sidebands of the target in adjacent auditory filters rather than the on-frequency component, thereby reducing the effective masking from the primary filter's output. This strategy is particularly effective when the masker is off-frequency, as it exploits the asymmetric shape of auditory filters, which have steeper slopes on the high-frequency side. Filter shapes are often modeled using the rounded exponential (roex) function, capturing the gradual roll-off and enabling quantitative predictions of masking reduction. Experimental studies, such as those employing notched-noise maskers, have generated masking curves as functions of frequency offset and intensity, revealing peak masking near zero offset that broadens and asymmetry increases with higher intensities—key data from Patterson and Moore's work on filter estimation.

Temporal Masking

Forward Masking

Forward masking, also known as pre-masking, refers to the phenomenon where the detection threshold of a target sound (probe) is elevated due to a preceding masker sound that ends shortly before the probe's onset, typically within a gap of 0 to 200 ms.^[16] This temporal separation distinguishes forward masking from simultaneous masking, where the masker and target overlap in time, highlighting sequential processing effects in the auditory system.^[17] The time course of forward masking exhibits an exponential decay following the masker's offset, with the masking effect diminishing as the interstimulus interval (time between masker offset and probe onset) increases. This recovery process has a time constant of approximately 50 ms at high frequencies, reflecting the auditory system's temporal resolution limits.^[18] The masking depth can be modeled as M(t) \approx A \cdot e^{-t / \tau}, where M(t) is the masking depth in dB, A is the initial masking depth, t is the interstimulus interval, and \tau is the time constant typically around 50-100 ms depending on frequency and intensity.^[19] Several factors influence the magnitude of forward masking, including masker intensity and frequency proximity to the probe; masking is stronger for higher masker levels and when the masker and probe share similar frequencies (on-frequency conditions).^[20] Physiologically, forward masking is associated with cochlear adaptation, where the basilar membrane's response to the masker persists, and neural recovery processes in the auditory nerve, which temporarily reduce responsiveness to subsequent stimuli.^[21]^[22] In psychoacoustic research, forward masking serves as a tool to investigate the temporal properties of auditory filters, providing insights into how the cochlea integrates sound over time and aiding the development of models for auditory processing.^[1]

Backward Masking

Backward masking, also known as post-masking, occurs when the perception of a target sound is impaired by a subsequent masker that begins shortly after the target's offset, typically within 0-50 ms, leading to elevated detection thresholds for the target. This phenomenon arises because the auditory system integrates sensory information over a brief temporal window, allowing the masker to interfere with the processing of the preceding signal. Unlike simultaneous masking, backward masking highlights the limits of temporal resolution in the auditory pathway, where the masker disrupts the neural representation of the target before it is fully encoded.^[23] The time course of backward masking is relatively short, with maximal effects observed at zero delay between target offset and masker onset, decaying rapidly to negligible levels by 20-50 ms post-target. For brief targets like 10-ms tones, masking thresholds can increase by approximately 20-35 dB at onset, but this effect diminishes with longer delays or target durations exceeding 20 ms. This brevity contrasts with forward masking, which persists longer due to slower neural recovery processes, illustrating an asymmetry in temporal masking where backward effects are weaker overall but peak more sharply. Mechanisms underlying backward masking involve both peripheral and central auditory processing, including temporal smearing of neural responses and interference within an integration window of approximately 200 ms for tonal signals. At the periphery, the masker may alter basilar membrane vibrations lingering from the target, while centrally, it suppresses signal-evoked activity in the auditory cortex, reducing dynamic range and firing rates. This disruption is more pronounced for short-duration targets, as the auditory system relies on integration to build a robust percept, which the masker interrupts.^[23] Experimental findings, such as those by Zwicker, demonstrate peak backward masking at zero delay, with overshoots up to 13 dB for a 2-ms, 5000-Hz tone masked by white noise, decreasing with spectral similarity between target and masker.^[24] Data from Zwicker and Fastl further show that backward masking exhibits an asymmetric profile compared to forward masking, with effects confined to shorter intervals and lower magnitudes, emphasizing the auditory system's forward-biased temporal processing. Factors enhancing backward masking include greater intensity differences and frequency similarity between target and masker, though these influences are less potent than in forward masking. For instance, masker levels of 50-90 dB SPL can elevate thresholds by 4-8 dB more at close frequencies, but dissimilar spectra (e.g., tone vs. noise) yield stronger initial overshoots. Brief target durations amplify the effect, underscoring the role of temporal integration limits.

Other Masking Phenomena

Informational Masking

Informational masking refers to the degradation in the detection, discrimination, or recognition of a target sound caused by competing sounds, where the interference arises not from the energetic overlap of their spectra or temporal envelopes at the auditory periphery, but from higher-level perceptual, cognitive, or attentional processes that introduce uncertainty and difficulty in segregating the target. This form of masking was first introduced by Pollack in 1975 as a distinct phenomenon beyond traditional energetic masking. Unlike energetic masking observed in simple tone-in-noise scenarios, informational masking involves complex auditory scenes where the maskers create confusion through similarity or perceptual grouping errors, diverting attention from the target. Key components of informational masking include the difficulty in auditory stream segregation when multiple similar sound sources are present, leading to confusion in identifying which sounds belong to the target versus the maskers, and failures in perceptual grouping that exacerbate uncertainty. For instance, in the cocktail party effect, listeners struggle to focus on one conversation amid multiple talkers due to overlapping acoustic cues and attentional demands, resulting in informational interference that hinders speech understanding. Similarity-based confusion is particularly pronounced when maskers share spectral or temporal characteristics with the target, such as in speech-on-speech masking where concurrent talkers with comparable voices or prosody increase the cognitive load required for segregation. These elements highlight how informational masking operates at central auditory processing stages, relying on linguistic and contextual cues rather than mere energy summation.^[25]^[26] Informational masking is typically measured through psychophysical tasks involving detection thresholds or speech identification in multi-source environments, often isolating its contribution by subtracting energetic masking estimates, such as those derived from ideal time-frequency segregation (ITFS) models that compute the maximum possible signal glimpses available after removing masker energy overlap. In multi-talker scenarios, informational masking can elevate thresholds by 10-20 dB or more beyond energetic components alone, as demonstrated in experiments where speech maskers cause significantly greater impairment than noise of equivalent energy. For example, speech intelligibility can drop to near zero with just a few competing talkers, reflecting losses up to 30 dB compared to 4 dB for noise maskers at detection threshold.^[27]^[25] Theoretical frameworks for informational masking, such as that proposed by Kidd et al. in 2023, emphasize the role of cognitive load in handling auditory scene complexity, integrating perceptual uncertainty with attentional selection mechanisms to explain masking release through cues like spatial separation or glimpsing opportunities in the signal. Factors influencing its magnitude include the acoustic similarity between target and maskers, which amplifies confusion, and linguistic familiarity, where maskers in an unfamiliar language reduce interference by minimizing semantic overlap. Informational masking is especially prominent in speech-on-speech masking, where it accounts for much of the difficulty in noisy social settings, but can be mitigated by spatial cues or brief temporal gaps that aid segregation. Seminal work by Neff in 1991 further linked informational masking to auditory attention, showing how divided focus in multi-tone identification tasks increases masking independent of energy overlap.^[25]^[28] Recent advances as of 2025 include brain-inspired algorithms that improve cocktail party listening by isolating talkers using narrow spatial tuning, demonstrating practical applications in enhancing speech separation in noisy environments.^[29]

Binaural Masking

Binaural masking refers to the alteration in the detection threshold of a target sound when the masker and target exhibit differences in interaural time differences (ITD) or interaural level differences (ILD) across the two ears. This phenomenon arises because the auditory system processes binaural cues to enhance signal detection in noisy environments, particularly when the target and masker are spatially separated. Unlike monaural masking, binaural masking leverages interaural disparities to reduce the effective masking, improving the signal-to-noise ratio perceived by the listener.^[30] The masking level difference (MLD), first described by Hirsh in 1948, quantifies the binaural advantage as the improvement in detection threshold when the target signal is presented out-of-phase across the ears relative to the in-phase masker noise. Typically, MLD values range from 10 to 15 dB for normal-hearing listeners, representing a substantial reduction in the required signal intensity for detection. The MLD is calculated using the formula:

\text{MLD} = 10 \log_{10} \left( \frac{I_{\text{monaural threshold}}}{I_{\text{binaural threshold}}} \right)

where I denotes the signal intensity at threshold, with the monaural condition corresponding to the homophasic (S_0N_0) configuration and the binaural to the antiphasic (S_{\pi}N_0). This effect is maximal for low-frequency tones in correlated broadband noise, as the auditory system exploits phase differences to segregate the target.^[31]^[32] Binaural masking release (BMLR) describes the overall improvement in signal detection due to these spatial cues, enabling better performance in complex acoustic scenes. A related phenomenon, the squelch effect, provides an additional binaural benefit of approximately 5-10 dB in speech understanding for hearing-impaired individuals, particularly those with bilateral cochlear implants, by suppressing noise through perceived source separation. MLD and BMLR are frequency-dependent, with the strongest effects below 1.5 kHz where ITD cues dominate, and diminish at higher frequencies where ILD becomes more relevant. These mechanisms are particularly valuable in reverberant noise environments, such as classrooms or auditoriums, where spatial separation aids in overcoming masking from reflections.^[33]^[34]^[30] As of 2025, research has advanced in characterizing the maturation of the binaural intelligibility level difference (BILD) in school-age children, aiding clinical assessments of central auditory development.^[35]

Physiological Mechanisms

Peripheral Mechanisms

Auditory masking at the peripheral level primarily arises from processes in the cochlea, where the basilar membrane's frequency-specific tuning leads to interference between sounds. The basilar membrane decomposes incoming sounds into frequency components along its tonotopic organization, with each location responding maximally to a characteristic frequency. When a masker and target sound stimulate overlapping regions of the basilar membrane, the masker's excitation can saturate the mechanical response, reducing the basilar membrane's vibration amplitude to the target by approximately 1 dB per dB increase in masker level near the characteristic frequency. This saturation occurs due to compressive nonlinearity in the cochlear amplifier, limiting the dynamic range and diminishing the target's neural representation.^[5]^[36] Suppression mechanisms further contribute to peripheral masking, particularly in two-tone interactions where one sound reduces the response to another. In two-tone suppression, a suppressor tone decreases the basilar membrane vibration and auditory nerve firing rate to a probe tone, with the effect most pronounced for off-frequency suppressors (e.g., an octave below the probe's characteristic frequency), shifting the rate-level function and elevating thresholds by 5-26 dB without altering discharge rates. This suppression grows faster for lower-frequency tones and originates from nonlinear cochlear mechanics. Adaptation plays a key role in forward masking, where preceding maskers lead to temporary reduction in sensitivity; while outer hair cell electromotility amplifies low-level sounds, adaptation in inner hair cells and synaptic processes post-maskers contributes to elevated thresholds, with recovery tied to slower neural adaptation rather than direct outer hair cell involvement.^[37]^[38]^[39] At the auditory nerve level, masking manifests as reduced spike rates and increased detection thresholds due to the masker's influence on cochlear output. In cat auditory nerve fibers, simultaneous masking grows at approximately 2 dB per dB for masker tones near or slightly above (10%) the fiber's characteristic frequency, reflecting hydromechanical spread of excitation that broadens the effective filter and overlaps with target responses. Post-masker thresholds rise due to this spread and adaptation, with noise maskers suppressing tone-evoked spikes by competing for neural resources in overlapping frequency channels. Electrophysiological data from animal models, such as cats, confirm these effects trace to early cochlear stages before central processing.^[40]^[5] Linear predictive models, such as the gammatone filterbank, simulate these peripheral processes by mimicking basilar membrane filtering with gamma-enveloped tones spaced on the equivalent rectangular bandwidth scale. These models capture masking by convolving inputs with filters that approximate cochlear frequency selectivity, predicting reduced target output in noise through linear superposition, and have been calibrated to human psychoacoustic data for tasks like tone-in-noise detection. Such simulations align with animal electrophysiology, reproducing suppression and spread without nonlinear extensions for basic energetic effects.^[41] The critical bandwidth, underlying simultaneous masking spread, emerges from the width of these peripheral filters, typically spanning 100-300 Hz at low frequencies. However, peripheral mechanisms primarily explain energetic masking, where physical overlap limits signal representation in the cochlea and auditory nerve, but fail to account for informational masking involving perceptual uncertainty at higher levels.^[5]^[42]

Central Mechanisms

Central mechanisms of auditory masking involve neural processing in the brainstem, midbrain, and cortex, where incoming signals from the periphery are integrated, modulated, and interpreted to influence perception in noisy environments. In the brainstem and midbrain, the inferior colliculus serves as a critical hub for integrating temporal cues, with neurons showing sound-evoked inhibition that underlies forward masking by suppressing responses to subsequent targets.^[43] Efferent feedback from the medial olivocochlear system further modulates these effects by dynamically adjusting cochlear gain, as demonstrated in a 2024 subcortical computational model that incorporates efferent control of cochlear gain to predict forward masking.^[44] This feedback mechanism helps mitigate masking by enhancing neural recovery times, particularly for brief temporal separations between masker and target. At the cortical level, the auditory cortex contributes to informational masking through attention-dependent processes and auditory scene analysis, where competing sounds interfere with target segregation beyond simple energetic overlap. Functional MRI evidence reveals reduced neural representation of target speech in masked conditions, with attentional focus modulating activity in primary and non-primary auditory areas to prioritize relevant streams while suppressing distractors.^[45] Subcortical delays in processing masked speech, observed via electrophysiological measures, further support central involvement, as responses become progressively smaller and delayed with increasing masking severity, reflecting integration lags that propagate to cortical stages.^[46] Recent advances highlight objective assessment and modeling of these central processes. Auditory steady-state response (ASSR) techniques enable non-invasive evaluation of masking effects, with a 2025 pilot study exploring the use of ASSR to assess auditory masking thresholds non-invasively, offering a tool to probe central temporal integration without behavioral reliance.^[47] Computational models incorporating efferent dynamics have improved predictions of forward masking, aligning simulated neural responses with human psychophysics by simulating brainstem-to-cortex pathways.^[44] Central mechanisms also account for asymmetries in masking, such as the persistence of backward masking despite peripheral recovery, due to central overwriting of target traces in short-term sensory memory rather than ongoing cochlear adaptation.^[48] In complex acoustic environments, these processes amplify peripheral excitation patterns through gain control and attentional biasing, enhancing target detection while exacerbating interference from informational maskers like fluctuating speech.^[49]

Applications

Audio Compression and Psychoacoustics

Auditory masking plays a central role in perceptual audio coding, where psychoacoustic models leverage masking thresholds to compress audio signals by quantizing components below human perception thresholds. In codecs such as MP3 (MPEG-1 Audio Layer III), developed in the 1990s, these models identify inaudible spectral components masked by dominant tones or noise, allowing for aggressive quantization without perceptible distortion. This approach exploits the ear's insensitivity to signals near masking sounds, enabling significant data reduction while preserving subjective audio quality. Simultaneous masking is particularly exploited in these systems through the concept of critical bands, which divide the spectrum into frequency regions analogous to the basilar membrane's filtering. Bit allocation algorithms assign fewer bits to masked subbands, prioritizing audible elements and hiding quantization noise within the masking threshold. Temporal masking predictions further mitigate artifacts like pre-echoes, where a strong signal masks subsequent weaker ones, by adjusting block sizes in the modified discrete cosine transform (MDCT) to align with auditory integration times. ISO/MPEG standards incorporate spreading functions to model frequency masking, simulating how masking energy spreads across critical bands via excitation patterns derived from psychophysical data. For instance, these models enable encoding at bit rates as low as 128 kbps with minimal perceptible loss for stereo music, as validated in listening tests showing transparency thresholds comparable to uncompressed CD audio. Modern codecs, such as Advanced Audio Coding (AAC) and Opus, build on these principles with refined psychoacoustic models incorporating auditory masking to achieve transparent quality at even lower bit rates, often below 96 kbps. As of 2025, the LC3 codec in Bluetooth Low Energy (LE) Audio, standardized by the Bluetooth SIG in 2020 and widely implemented in devices by 2024, uses advanced masking thresholds for efficient wireless streaming, supporting features like Auracast for broadcast audio to multiple listeners, including hearing aids, with reduced latency and power consumption.^[50] In research applications, masking principles inform the tuning of auditory filters for virtual acoustics, where simulated environments replicate masking effects to enhance spatial audio rendering. Models are rigorously tested against human detection thresholds in controlled experiments, refining parameters like the masking slope for better fidelity in immersive systems. However, a key limitation is the over-reliance on energetic masking, which often underperforms in complex musical passages where informational masking—arising from perceptual grouping—degrades compression efficiency and introduces audible artifacts.

Hearing Aids and Clinical Uses

In audiological diagnostics, clinical masking is employed during pure-tone audiometry to isolate thresholds in the test ear by introducing noise to the non-test ear, preventing cross-hearing via bone or air conduction pathways.^[51] Masking is required for air conduction when interaural differences exceed 40 dB (or 55 dB with insert earphones) and for bone conduction when air-bone gaps surpass 10 dB or bone conduction in one ear is better by 40 dB than the contralateral air conduction threshold.^[51] This technique ensures accurate differentiation between conductive and sensorineural hearing loss, with procedures involving incremental noise levels until a plateau threshold is achieved, typically using narrowband noise at 10-20 dB above the non-test ear's expected threshold.^[51] Cochlear dead regions, areas of dysfunctional inner hair cells, are identified through off-frequency listening deficits where signals are detected via adjacent viable regions, leading to elevated masked thresholds.^[52] The threshold equalizing noise (TEN) test diagnoses these by presenting pure tones in noise; a dead region is indicated if the masked threshold exceeds the TEN level by at least 10 dB per equivalent rectangular bandwidth (ERB) and 10 dB above the absolute threshold, often revealing perceptual distortions like noise-like tones in affected frequencies.^[52] Modern hearing aids incorporate noise reduction algorithms based on auditory masking thresholds to suppress background interference while preserving speech cues.^[53] These algorithms, such as the generalized minimum mean square error estimator adapted for masking (GMMSE-AMT[ERB]), estimate simultaneous and temporal masking using ERB-scaled filters tailored to hearing loss profiles, reducing noise gain in low-signal-to-noise ratio bands without distorting speech intelligibility.^[53] As of 2025, AI-enhanced systems in hearing aids further refine masking-based noise suppression by dynamically adjusting to acoustic scenes, improving speech-in-noise performance. Directional microphones in binaural hearing aids exploit spatial release from masking by enhancing frontal signals and attenuating off-axis noise, providing up to 5-10 dB signal-to-noise ratio improvements in reverberant environments through interaural time and level differences.^[54] Bluetooth LE Audio integration allows direct high-quality streaming to aids, leveraging masking models for efficient low-bitrate transmission in applications like Auracast for public announcements.^[55] In cochlear implants, channel allocation strategies using n-of-m approaches, such as SNR-based methods like the IdBM (intelligibility-based mask estimation), select the most prominent spectral envelopes from target-dominated channels (signal-to-noise ratio ≥0 dB) over masker-dominated ones to minimize masking effects and provide clearer speech representation.^[56] This reduces energetic and informational masking by limiting channel interactions, with studies showing improved sentence recognition in noise by 10-20% compared to non-selective strategies like CIS, particularly when avoiding overlap in competing talkers.^[56] Hearing-impaired individuals often face heightened informational masking challenges in noisy environments, where perceptual segregation of speech streams is impaired.^[57] Clinical phenomena such as hyperacusis, an exaggerated sound intolerance often co-occurring with hearing impairment, can be managed with low-level masking noise to desensitize the auditory system and reduce discomfort from everyday sounds.^[58] Impaired ears exhibit reduced masking release, with hearing-impaired listeners showing only 0-2 dB benefit in fluctuating noise versus 4-8 dB in normal-hearing individuals, due to diminished audibility during noise dips.^[59] Recent applications of auditory steady-state responses (ASSR) in 2025 pediatric assessments provide objective thresholds for infants, incorporating masking for high-intensity stimuli to prevent contralateral contamination and aiding early identification of mild losses in non-responsive children.^[60] Sound therapy for tinnitus relief leverages controlled masking with broadband noise generators, delivering partial masking at or slightly above hearing thresholds for 8-10 hours daily to promote habituation and reduce perceived loudness.^[61] Integrated into tinnitus retraining therapy, this approach may provide subjective improvements in annoyance for 60-80% of patients over 12-24 months according to some studies, though systematic reviews indicate limited overall evidence of efficacy; often using behind-the-ear devices without reported adverse effects.^[61]^[62]

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Recovery from short-term adaptation was measured in single neurons in the cochlear nucleus using a forward masking stimulus paradigm.
[23]
https://doi.org/10.1152/jn.00114.2018
[24]
https://core.ac.uk/download/pdf/215249778.pdf
[25]
https://doi.org/10.1121/AT.2023.19.1.29
[26]
https://doi.org/10.1121/1.1907229
[27]
Informational masking and auditory attention - PubMed
Informational masking is broadly defined as a degradation of auditory detection or discrimination of a signal embedded in a context of other similar sounds.
[28]
Binaural masking level difference for pure tone signals - PMC
Jul 4, 2023 · The binaural masking level difference (BMLD) is a psychoacoustic method to determine binaural interaction and central auditory processes.Missing: MLD | Show results with:MLD
[29]
Masking Level Difference (MLD) - AC40 - Interacoustics
Feb 10, 2022 · The masking level difference (MLD) is the improvement in detecting a tone or speech in noise when the phase of the tone or the noise is reversed by 180 degrees.Missing: psychoacoustics | Show results with:psychoacoustics
[30]
Masking level differences under two different measurement conditions
Masking level difference (MLD) is a binaural interaction phenomenon that describes the improvement in the detection threshold due to phase differences of ...Missing: psychoacoustics | Show results with:psychoacoustics
[31]
[PDF] SPATIAL RELEASE FROM MASKING - Acoustics Today
A simpler version of the BILD is the binaural masking level difference (BMLD), where a target ... al listening condition (known as the squelch effect).
[32]
[PDF] Masking Level Difference (MLD): Literature Review
Mar 10, 2017 · Masking Level Difference composes a tests set for the central auditory processing behavioral evaluation and estimates decoding binaural.
[33]
Masking of sounds by a background noise – cochlear mechanical ...
In the search for cochlear correlates of auditory masking by noise stimuli, we recorded basilar membrane (BM) vibrations evoked by either tone or click signals ...
[34]
The role of suppression in psychophysical tone-on-tone masking - NIH
This study tested the hypothesis that suppression contributes to the difference between simultaneous masking (SM) and forward masking (FM).
[35]
Masking by Inaudible Sounds and the Linearity of Temporal ...
Aug 23, 2006 · This phenomenon, known as “forward masking,” is usually quantified by measuring how much the just-detectable level (or threshold) of a target ...Missing: probe | Show results with:probe
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Adaptation in auditory processing | Physiological Reviews
Jan 3, 2023 · Release of acetylcholine from medial olivocochlear neurons inhibits the electromotility exhibited by outer hair cells, which is responsible for ...<|separator|>
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Growth rate of simultaneous masking in cat auditory-nerve fibers ...
The growth rate of maskings averaged approximately 2 dB/dB, was typically largest for tones about 10% above fiber CF, and decreased at higher and lower ...
[38]
[PDF] History and Future of Auditory Filter Models - Google Research
Abstract—Auditory filter models have a history of over a hundred years, with explicit bio-mimetic inspiration at many stages along the way.
[39]
Determining the energetic and informational components of speech ...
SNHL listeners demonstrated both greater energetic and informational masking as well as higher glimpsed thresholds.
[40]
Temporal Masking Reveals Properties of Sound-Evoked Inhibition in ...
The inferior colliculus (IC) is the first place in the central auditory pathway where duration-selective neurons are found.
[41]
A Subcortical Model for Auditory Forward Masking with Efferent ...
Sep 4, 2024 · A recent computational model of the auditory subcortex including medial olivocochlear efferents generates forward masking, an increase in detection threshold.Missing: seminal | Show results with:seminal
[42]
FMRI speech tracking in primary and non-primary auditory cortex ...
Sep 30, 2024 · These results indicate that the fMRI signal tracks cortical responses and attention effects related to continuous speech.
[43]
The effect of speech masking on the human subcortical response to ...
Dec 11, 2024 · We show that the subcortical response to masked speech becomes smaller and increasingly delayed as the masking becomes more severe.
[44]
https://www.eneuro.org/content/11/9/ENEURO.0365-24.2024
[45]
Backward Masking - an overview | ScienceDirect Topics
This confirms that the critical aspect of backward masking is overwriting of the target's sensory memory by the mask, not the mere proximity of target and mask.
[46]
Hearing in Complex Environments: Auditory Gain Control, Attention ...
Feb 10, 2022 · Thus, while peripheral mechanisms certainly contribute to perceptual alterations associated with cochlear degeneration, there is growing ...
[47]
Audiology Clinical Masking - StatPearls - NCBI Bookshelf - NIH
Mar 31, 2022 · Therefore, clinical masking is required when the difference in hearing thresholds between the ears is greater than the interaural attenuation.
[48]
Dead Regions in the Cochlea: Diagnosis, Perceptual ...
Off-frequency listening can occur even in normally hearing people, especially when a signal has to be detected in the presence of another sound. However, it ...
[49]
An Auditory-Masking-Threshold-Based Noise Suppression ...
Nov 10, 2005 · This study describes a new noise suppression scheme for hearing aid applications based on the auditory masking threshold (AMT) in ...Missing: reduction | Show results with:reduction
[50]
Unilateral and bilateral hearing aids, spatial release from masking ...
Jul 11, 2013 · Spatial release from masking (SRM) was tested within the first week of fitting and after 12 weeks hearing aid use for unilateral and ...
[51]
A new sound coding strategy for suppressing noise in cochlear ... - NIH
The new criterion selects target-dominated (SNR⩾0 dB) channels and discards masker-dominated (SNR<0 dB) channels. Experiment 1 assessed cochlear implant users' ...Missing: allocation | Show results with:allocation
[52]
Speech Understanding With Various Maskers in Cochlear-Implant ...
Jul 19, 2018 · For example, informational masking can occur when a competing talker interferes with a target talker due to difficulty perceptually segregating ...
[53]
Evaluation and Selection of Maskers and Other Devices Used in the ...
We review not only the phenomenon of tinnitus masking, but also discuss the use of controlled levels of noise in the treatment of hyperacusis, an exaggerated or ...
[54]
Masking release for hearing-impaired listeners: The effect of ...
The current study demonstrates that EEQ processing leads to a greater release of masking for HI listeners in certain types of fluctuating noise (in particular, ...Missing: hyperacusis | Show results with:hyperacusis
[55]
Auditory Steady-State Responses for Detecting Mild Hearing Loss in ...
Jul 15, 2025 · Our conclusion is that ASSR assessments via bone are effective in the pediatric population, although in the adult population, they should be ...
[56]
Sound therapy (masking) in the management of tinnitus in adults
Initial approaches to sound therapy involved 'complete masking' whereby the masking noise is raised in intensity until the tinnitus becomes inaudible (Coles ...