2Pure-Tone Audiometry (incl. high-frequency)

FWhat the pure-tone audiogram measures

Pure-tone audiometry (PTA) quantifies the quietest tone a listener can detect at each frequency, conventionally from 250 Hz to 8 kHz, expressed in decibels hearing level (dB HL). Two routes are tested: air conduction (through the earphone, testing the whole auditory pathway) and bone conduction (through a vibrator on the mastoid, bypassing the outer and middle ear). The gap between them — the air–bone gap — localises the lesion. No gap with elevated thresholds means sensorineural loss; a gap means a conductive component.

In tinnitus this matters because the type of loss reshapes the differential: a purely sensorineural high-frequency loss is the signature of the common cochlear tinnitus, whereas a conductive picture redirects attention to the middle ear or to a third-window lesion [2005].

TThe typical tinnitus audiogram: high-frequency slope and the noise notch

The single most common audiometric finding in tinnitus is high-frequency sensorineural hearing loss [2005]. Two patterns recur. The noise notch is a focal dip centred at 3–6 kHz (classically 4 kHz) with partial recovery at 8 kHz — the fingerprint of noise-induced cochlear injury. The sloping presbycusic pattern is a smooth downhill curve worsening toward the high frequencies, typical of age-related loss.

The cochlear region of greatest damage is also, characteristically, the region from which the tinnitus arises. This is the central insight of the central-gain model: deafferentation in the high-frequency cochlea removes inhibitory drive, the central auditory system increases its gain to compensate, and a phantom tone emerges at frequencies bordering the loss [2011].

TBeyond 8 kHz: extended high-frequency audiometry

The conventional audiogram stops at 8 kHz, but cochlear damage often begins higher. Extended high-frequency (EHF) audiometry tests 9–16 kHz (and beyond) and frequently reveals loss in tinnitus patients whose standard audiogram is entirely normal [2015]. A meta-analysis confirms that EHF thresholds are significantly worse in tinnitus patients with a normal conventional audiogram than in matched controls, establishing EHF testing as the most direct way to expose this “hidden” cochlear contribution [2022].

Clinically, EHF audiometry rescues the patient who is told their hearing is “normal” despite obvious tinnitus, gives a mechanistic explanation, and supports counselling about noise protection. It is especially useful early in noise and ototoxic injury, where the highest frequencies are damaged first.

CTinnitus pitch sits at the audiometric edge

When the perceived pitch of the tinnitus is matched psychoacoustically (covered in a later module) and superimposed on the audiogram, it characteristically falls at or just within the edge of the hearing loss — the frequency region where thresholds begin to deteriorate. This edge phenomenon is one of the most robust observations in tinnitus and is exactly what the central-gain model predicts: maladaptive plasticity is concentrated at the border between intact and deafferented cochlear input [2011].

For the clinician this turns the audiogram into a predictive tool: the shape of the loss anticipates where the tinnitus pitch will lie, the high-frequency slope explains its typically high pitch, and a normal standard audiogram with high-pitched tinnitus is the cue to test extended high frequencies rather than to dismiss the complaint [2015].