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An audiogram is the primary tool for detecting noise-induced hearing loss — but most workers who receive one in an occupational health setting have never had it explained to them. This guide covers what the audiogram shows, how to read the results, what different patterns mean, and why it matters for hearing conservation compliance.
Soundtrace generates OSHA-compliant audiograms with automated baseline comparison, professional supervisor review, and employee-friendly results summaries — so workers understand what their audiogram means and employers have the documentation OSHA requires.
An audiogram is the graph produced by pure-tone audiometric testing. It plots an individual’s hearing thresholds — the softest level at which they can consistently detect a tone — at multiple frequencies across both ears.
The test works by presenting tones at specific frequencies through calibrated headphones, starting at clearly audible levels and decreasing until the softest level the person can consistently detect is found. This threshold level, measured in decibels hearing level (dB HL), is plotted on the audiogram for each frequency tested.
In occupational audiometry, OSHA requires testing at six frequencies: 500, 1000, 2000, 3000, 4000, and 6000 Hz. These frequencies span the range most relevant for speech understanding and most vulnerable to noise-induced damage. Some programs also test at 8000 Hz; testing above 8000 Hz (extended high-frequency audiometry) can detect early ototoxic damage but is not required by OSHA.
The audiogram is not a pass/fail test in the occupational context — it’s a surveillance record. Its primary value comes from comparing results over time: each annual audiogram is compared to the baseline to detect progressive change, not evaluated against population norms alone.
▶ Bottom line: The audiogram records the softest sounds a person can hear at each frequency. Its occupational value is in tracking change over time — the baseline comparison is what makes it a hearing conservation tool rather than just a snapshot.
An audiogram has two axes:
Horizontal axis (X-axis): Frequency in Hertz (Hz). Frequencies increase from left to right: 250, 500, 1000, 2000, 3000, 4000, 6000, 8000 Hz. Low frequencies (left) correspond to low-pitched sounds; high frequencies (right) correspond to high-pitched sounds. Normal speech occurs primarily in the 500–4000 Hz range.
Vertical axis (Y-axis): Hearing Threshold Level in dB HL. The scale runs from –10 at the top to 110 or 120 at the bottom. Better hearing is toward the top of the graph (lower numbers); worse hearing is toward the bottom. 0 dB HL is not silence — it is the average threshold of young adults with normal hearing. A threshold of 25 dB HL means the softest tone the person can hear is 25 dB above the normal young adult reference.
Symbols: Standard audiometric notation uses O (circle) for right ear air conduction results and X for left ear air conduction results. Bone conduction results (used to differentiate sensorineural from conductive loss) use different symbols: < for right ear, > for left ear. In occupational audiometry, air conduction is the primary measurement.
The plotted results for each ear are connected by lines, creating the audiogram “curve” that visually represents the hearing profile across frequencies.
▶ Bottom line: Reading an audiogram: better hearing is toward the upper-left (low thresholds, low frequencies). Worse hearing is toward the lower-right. A notch dipping below the rest of the curve at 4000 Hz is the noise-induced hearing loss signature.
A normal audiogram for a young adult without noise exposure shows:
As people age without noise exposure, a gradual high-frequency decline appears — presbycusis. This age-related pattern shows relatively normal low-frequency thresholds sloping to elevated thresholds in the high frequencies, beginning typically in the 40s and progressing with age. This presbycusis pattern is important to distinguish from noise-induced loss because noise-induced loss produces a characteristic notch rather than a slope, and is centered at 4000 Hz rather than affecting the highest frequencies first.
For workers entering a hearing conservation program, the baseline audiogram establishes their individual starting point. This baseline may already show some degree of hearing loss from prior noise exposure, recreational noise, or age-related change. The baseline is the reference, not a normative comparison.
▶ Bottom line: Normal occupational baselines are not always perfectly flat curves at 0 dB HL. New hires may come in with pre-existing loss. The baseline documents the starting point — which is why it matters so much to establish it accurately at enrollment, before further occupational noise exposure occurs.
Noise-induced hearing loss produces a distinctive audiogram signature:
The 4000 Hz notch: Hearing thresholds are relatively normal at low and mid frequencies (500–2000 Hz), drop significantly at 3000–4000 Hz, and partially recover at 6000–8000 Hz. This notch pattern reflects the anatomy of the cochlea: the region tuned to 4000 Hz receives disproportionate mechanical stress from most industrial noise spectra and is positioned at a particularly vulnerable point in the cochlear structure.
Bilateral and roughly symmetric: Because occupational noise typically reaches both ears simultaneously, noise-induced loss is usually bilateral (both ears affected) and approximately symmetric. Significant asymmetry between ears — more than 15–20 dB difference at 4000 Hz — suggests a cause other than symmetric bilateral noise exposure and warrants further evaluation.
Progression over time: In early stages, the notch is confined to the 4000 Hz area. With continued noise exposure, the notch deepens and spreads to adjacent frequencies. When the notch extends into 2000–3000 Hz, speech understanding begins to be affected. The progression from isolated 4000 Hz notch to broad high-frequency loss can take years to decades depending on noise level, hearing protection use, and individual susceptibility.
The characteristic 4000 Hz notch can appear even before a Standard Threshold Shift is detected against the OSHA STS criteria, which average thresholds at 2000, 3000, and 4000 Hz. A developing notch that doesn’t yet reach 10 dB average is a clinical signal worth flagging for enhanced surveillance — the intervention window is still open.
▶ Bottom line: A deepening notch at 4000 Hz on successive annual audiograms is the early audiometric signature of noise-induced hearing loss. It predates functional hearing impairment by years — which is why annual surveillance catches it in the window where intervention can change the trajectory.
Not all audiogram patterns represent noise-induced hearing loss. The professional supervisor must consider alternative diagnoses when the pattern is inconsistent with noise-induced loss:
High-frequency sloping loss without a notch: A gradual slope from normal low-frequency hearing to poorer high-frequency thresholds without a notch is more typical of presbycusis (age-related hearing loss) than noise-induced loss. Noise and age interact, however, so occupational noise may accelerate age-related decline.
Asymmetric loss: Significantly more hearing loss in one ear than the other (more than 15–20 dB at 4000 Hz) is not typical of noise-induced loss from bilateral industrial noise exposure. Asymmetric loss may indicate acoustic neuroma, Meniere’s disease, prior acoustic trauma to one ear, or noise from a localized source to one side (e.g., a machine on the worker’s right side).
Low-frequency or flat loss: Hearing loss affecting low frequencies equally with or more than high frequencies suggests Meniere’s disease (particularly with episodic symptoms), autoimmune inner ear disease, or conductive hearing loss (middle ear pathology). These patterns are not typical of occupational noise and warrant medical referral.
Sudden large change: A dramatic threshold shift between annual audiograms — far larger than expected for a year of exposure — may indicate sudden sensorineural hearing loss (which can benefit from urgent treatment), acute acoustic trauma from a specific event, or medication effects. This pattern warrants prompt medical evaluation, not just retest scheduling.
▶ Bottom line: Pattern recognition is why the professional supervisor — not just automated threshold comparison software — is required to review audiograms. An algorithm can detect an STS; only a clinical professional can evaluate whether the pattern suggests something beyond occupational noise requiring different action.
Under OSHA 1910.95(g)(10)(i), a Standard Threshold Shift is defined as a change in hearing threshold, relative to the baseline audiogram, of an average of 10 dB or more at 2000, 3000, and 4000 Hz in either ear.
The STS calculation:
Age correction is optionally applied before this calculation using OSHA Appendix F tables, which predict expected threshold change due to aging alone. If the age-corrected shift is less than 10 dB average, the recordability calculation may not apply (though the 1910.95 follow-up obligations still need professional supervisor review).
The STS triggers a required employer action sequence: notification within 21 days, hearing protection reassessment, optional retest within 30 days, and OSHA 300 recordability evaluation.
Every audiogram conducted in an occupational hearing conservation program is simultaneously a clinical document and a compliance record. It must be:
An audiogram conducted outside these requirements — with uncalibrated equipment, in an acoustically inadequate environment, by an unqualified technician, or without professional supervisor review — is not an OSHA-compliant audiogram regardless of whether the threshold values are recorded correctly.
Soundtrace produces compliant audiograms with automated baseline comparison, professional audiologist review, and 30-year digital records retention — all without a sound booth.
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