Overview & Audiometric Principles
Pure-tone audiometry is the gold-standard clinical mechanism utilized to map the absolute limits of human auditory perception across the range of speech frequencies. This online simulator mimics the behavior of diagnostic standard clinical audiometers, mapping the intensity of pure acoustic sine wave presentations against standard Hearing Levels ($\text{dB HL}$). Hearing Level is a biological normalization reference, contrasting a user's sensory sensitivity against the established normal hearing threshold (Reference Equivalent Threshold Sound Pressure Levels, or $\text{RETSPL}$).
Unlike standard logarithmic physical Sound Pressure Levels ($\text{dB SPL}$), defined physically by:
$$L_p = 20 \log_{10} \left( \frac{p}{p_0} \right) \text{ dB SPL}$$
where $p_0 = 20 \ \mu\text{Pa}$ (the absolute lower limit of standard biological hearing sensitivity at $1000\text{ Hz}$), $\text{dB HL}$ normalizes this threshold to $0 \text{ dB HL}$ across all frequencies. Human hearing is naturally less sensitive to extreme low and high frequencies due to the impedance matches of the middle ear ossicles and acoustic canal geometry. Consequently, the physical energy required to achieve a $0 \text{ dB HL}$ clinical perception varies heavily by frequency. This relationship is integrated within our computational synthesis engine, compensating with custom calibration offsets:
$$A(f) = 10^{\frac{H - \text{RETSPL}(f) - \Theta_{\text{sys}}}{20}} \times G_{\text{calib}}$$
where $H$ is the chosen target hearing intensity in $\text{dB HL}$, $\text{RETSPL}(f)$ represent frequency-specific standard compensation curves, $\Theta_{\text{sys}}$ is system baseline safe headroom, and $G_{\text{calib}}$ is overall system attenuation to protect user hardware and cochlear structures from high-energy acoustic overload.
The human peripheral auditory system acts as a biological frequency analyzer. Acoustic waves entering the external auditory meatus strike the tympanic membrane, translating physical pressure oscillations into mechanical displacements. These vibrations are amplified through the ossicular chain (malleus, incus, stapes) and delivered to the oval window of the fluid-filled cochlea. Inside, pressure differentials between the scala vestibuli and scala tympani create a traveling wave along the basilar membrane. The physical properties of this membrane vary continuously: it is narrow and stiff at the base (highly responsive to high frequencies) and wide and floppy at the apex (responsive to low frequencies), establishing a tonotopic map.
Sensory transduction is carried out by the organ of Corti. Deflection of inner hair cell stereocilia against the tectorial membrane opens mechanically gated ion channels, initiating potassium influx, depolarizing the cell membrane, and firing action potentials along the cochlear nerve. In clinical pathology, structural or metabolic compromises along this pathway lead to hearing deficits. Conducting air-conduction sweeps allows clinicians to characterize these losses.
⚠️ Diagnostic Warning & Disclaimer
This simulator operates as an educational and behavioral sensory visualization lab. Because commercial consumer headphones, system sound limits, micro-circuitry pre-amplifiers, and ambient room noise curves are not standardized or professionally calibrated in situ using an artificial mastoid ear-coupler (ANSI S3.6), the resulting output coordinates must NOT be treated as a definitive clinical diagnosis. If you detect asymmetrical thresholds, significant high-frequency drop-offs, or suspect hearing loss, please arrange a formal examination with a licensed clinical audiologist.
Step-by-Step Operation Guide
Conducting an interactive behavioral test relies on precise sensory detection. Use this structured workflow to optimize your testing sequence:
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Optimal Acoustic Configuration: Seat yourself in a static, noise-isolated room. Connect a high-quality pair of stereo headphones, ensuring the Left and Right physical channels are oriented correctly on your ears.
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Audio Activation: Click the "🔇 SOUND OFF" button in the upper control tier. This initiates the standard Web Audio pipeline. It will transform to "🔊 SOUND ON" with an active green glowing indicator.
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Frequency Selection: Click a target frequency button (standard practice starts at $1000\text{ Hz}$ to isolate cognitive adaptation, then sweeps upwards through $2000$, $4000$, and $8000\text{ Hz}$ before returning to verify thresholds at lower bands like $500$, $250$, and $125\text{ Hz}$).
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Modality Choices: Use the "Stimulus Presentation Mode" dropdown. Clinical audiologists prefer **Pulsed Tones** (a rhythmic sequence of $250\text{ ms}$ sine pulses) as it prevents sensory habituation and allows the auditory cortex to segment the external trigger from internal tinnitus.
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Ascending Threshold Determination: Move the "Hearing Level" slider down to $0\text{ dB HL}$ (or when the tone is completely silent). Gradually drag the slider upwards in small intervals ($5\text{ dB}$ blocks) until you can barely hear the tone. This is your sensory threshold.
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Marking Thresholds: Click the "Record Threshold" button. A marker will lock onto the visualizer graph: a Blue "X" represents the Left Ear, and a Red "O" represents the Right Ear. Repeat this action for the opposing ear across all targeted frequency channels.
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Loading Profile Cases: Select from "Clinical Case Presets" to instantly project textbook conditions, such as high-frequency presbycusis or noise-induced notches, directly onto the interactive canvas for analysis and comparison.
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Data Capture: Click "Export Plot as Image" to generate an identical, pixel-perfect copy of your clinical audiogram canvas containing your recorded hearing threshold curves.
To trace a comprehensive diagnostic hearing curve, you should follow the clinical ascending threshold method. For each chosen test frequency, reduce the sound volume to an inaudible level, then increase it in $5\text{ dB}$ steps until the patient signals sound detection. After detection, lower the level by $10\text{ dB}$ and begin another ascending climb. A threshold is defined as the lowest level at which a response is recorded for at least $50\%$ of the trials on ascending sweeps.
Engineering & Software Architecture
The underlying application engine leverages modern browser technologies optimized for performance, visual quality, and acoustic accuracy. To eliminate layout shifts, infinite canvas expansion loops, and external scaling dependencies, we bypassed common Chart.js structures to build a custom high-performance, high-DPI HTML5 $2\text{D}$ Canvas plotting environment.
During screen-scaling, orientation shifts, or high-DPI (Retina) changes, the engine captures the browser window’s backing store multipliers:
$$\text{DPR} = \text{window.devicePixelRatio} \ || \ 1$$
The engine resizes the internal drawing buffer of the canvas to match the physical screen pixels while keeping CSS dimensions stable, preventing pixelation.
The digital signal synthesizer relies on the Web Audio API. Pure, mathematically correct sine waves are generated using a native browser OscillatorNode:
$$s(t) = A \cdot \sin(2\pi f t)$$
This digital signal is routed to a stereo ChannelMergerNode, which isolates the auditory signal to either the Left (Index $0$) or Right (Index $1$) channel. This ensures zero acoustic crosstalk between ears. To prevent transient "clicks" or pop artifacts on the headphones when changing volume or starting/stopping signals, we use smooth exponential ramping parameters on the output amplifier:
$$\text{gain}(t) = \text{gain}_{\text{target}} \cdot e^{-\lambda(t - t_0)}$$
This dynamic ramping is driven via the sub-millisecond audio timeline Scheduler (AudioParam.setTargetAtTime), ensuring that all transitions are completely transparent to the user.
A high-resolution clinical frequency spectrum analyzer (oscilloscope) is embedded directly at the bottom of the canvas. This parses the output signals using a fast Fourier transform algorithm (FFT) inside an AnalyserNode, mapping actual wave generation curves in real time for diagnostic confirmation.
The vector canvas coordinate mapping converts clinical variables to physical pixels. The X coordinate uses logarithmic octave divisions, while the Y coordinate features inverted mapping (mapping $0\text{ dB}$ near the top edge and $110\text{ dB}$ near the bottom):
$$y_{\text{pixel}} = y_{\text{padding\_top}} + \left(\frac{H - H_{\text{min}}}{H_{\text{max}} - H_{\text{min}}}\right) \cdot \text{plot\_height}$$
This ensures that the plotted output strictly aligns with established standard medical layout rules, maintaining spatial accuracy across all viewport form factors.
Future Clinical Enhancements
A roadmap of potential future improvements focuses on expanding diagnostic automation and improving system precision:
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Adaptive Hughson-Westlake Staircase: An automated testing loop implementing the clinical Hughson-Westlake algorithm (an iterative "Down $10 \text{ dB}$, Up $5 \text{ dB}$" sweep) to scientifically detect true hearing thresholds without human manual input.
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Microphone Ambient Decibel Noise Monitor: Active background-noise polling using the user's web microphone, displaying warnings if local room noise levels exceed critical thresholds ($\sim 40 \text{ dBA}$) that could mask high-frequency hearing detection.
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Bone Conduction & Tympanometry Layers: Addition of alternative diagnostic mapping structures, including standard clinical symbols for masked and unmasked bone conduction ($\langle$, $\rangle$, $[$, $]$).
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External Hardware Coupler Calibrations: Custom calibration profiles matching popular consumer hardware (Apple AirPods, Sony WH-1000XM series) using laboratory transfer functions to yield closer approximations of true decibel levels.
Implementing WebRTC-based local loopback checks can help detect ambient background interference before a test begins. By sampling local room noise through the user's built-in microphone, the software can run an ongoing FFT analysis to ensure high low-frequency noise (e.g., HVAC hum) does not mask low-frequency test tones. Additionally, integrating Speech Reception Threshold (SRT) testing using pre-recorded spondaic words would expand this tool from basic tone mapping into a comprehensive diagnostic suite.
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