7Notched and Customised Sound Therapy

FFrom masking to shaping the spectrum

Conventional sound therapy delivers broadband noise across all frequencies. Tailored sound therapy takes a different tack: it removes or rearranges energy at specific frequencies, usually those near the tinnitus pitch, in the hope of driving favourable plastic change in the deafferented region. Instead of covering the tinnitus, these approaches try to retune the maladaptive map that produces it.

The two best-known families are notched stimulation, which deletes a band of frequencies around the tinnitus pitch, and customised or personalised stimulation, which is individually fitted to the patient’s tinnitus and audiometric profile. Both rest on the idea that the abnormal central activity is frequency-specific and therefore potentially treatable with a frequency-specific stimulus.

TThe lateral-inhibition rationale for notching

Why remove sound at the tinnitus frequency rather than add it? The logic is lateral inhibition. Neurons tuned to a given frequency inhibit their neighbours; if a band of frequencies is notched out of the stimulus, the auditory neurons flanking the notch are strongly driven and, through lateral inhibition, suppress the under-stimulated neurons inside the notch — precisely the hyperactive, deafferented neurons thought to generate the tinnitus.

The landmark demonstration came from Okamoto and colleagues, who had patients listen to their favourite music with an energy notch one octave wide centred on their tinnitus pitch. After twelve months, the notched-music group reported reduced tinnitus loudness and showed reduced auditory-cortex activity at the tinnitus frequency, compared with controls who listened to placebo-notched music [2010]. The effect was specific to notching at the tinnitus frequency, supporting the lateral-inhibition account.

TCustomised noise, fractal tones and coordinated reset

Beyond notched music, several customised approaches are in use. Fractal tones — non-repeating, melodic, self-similar sequences built into many hearing aids — aim to provide pleasant, unpredictable enrichment that the brain does not fixate on; they were popularised through acoustic stimuli delivered via hearing aids [2010]. Customised broadband noise is shaped to the individual’s hearing loss and tinnitus pitch rather than presented flat.

A more theory-driven approach is acoustic coordinated-reset (CR) neuromodulation, developed by Tass and colleagues. Here a sequence of tones around the tinnitus frequency is delivered in a specific spatiotemporal pattern designed to desynchronise the pathologically synchronous neural population. An early study reported reductions in tinnitus loudness and synchrony with acoustic CR [2012], though the approach has not been widely replicated at scale.

CThe mixed evidence

It is important to be candid: tailored sound therapy is promising but unproven as a class. The Okamoto notched-music result is elegant and frequency-specific, but the sample was small and later replication attempts have been inconsistent, particularly for patients whose tinnitus is noise-like rather than tonal — notching only makes sense when there is a definable tinnitus frequency to notch around.

The Cochrane review of sound therapy concluded that the overall quality of evidence for sound-based interventions is low and that no specific sound type has been shown to be clearly superior [2018]. Acoustic CR has not lived up to its early promise in independent trials. The pragmatic position is that tailored sounds are low-risk and may help selected, well-characterised patients, but should not be sold as established cures [2013].

CChoosing a tailored approach in practice

Tailored sound therapy is most defensible when three conditions are met: the patient has a clearly tonal tinnitus with a reproducible pitch match; their hearing loss is mild enough that flanking frequencies can be adequately stimulated; and they are motivated to use the stimulus consistently for months. Notched music suits patients who already enjoy listening to music; fractal tones suit hearing-aid users who want built-in enrichment.

The honest counselling point is that the expected effect is modest and gradual, and that personalisation improves comfort and adherence more reliably than it improves the underlying neural effect. As with all sound therapy, realistic expectations and sustained use matter more than the specific algorithm chosen.