Tinnitus maskers are a range of devices based on simple white noise machines used to add natural or artificial sound into a tinnitus sufferer's environment in order to mask or cover up the ringing. The noise is supplied by a sound generator, which may reside in or above the ear or be placed on a table or elsewhere in the environment. The noise is usually white noise or music, but in some cases, it may be patterned sound or specially tailored sound based on the characteristics of the person's tinnitus. The perceived loudness of tinnitus, called sensation level (SL), is how much louder the tinnitus is above the ambient noise of the environment. By raising the ambient level of noise (playing white noise into the ear), the apparent loudness of tinnitus is reduced. The noise level is close to and usually somewhat louder than the perceived loudness of the tinnitus. The generated noise is designed to be a calming, less intrusive sound than the ringing or hissing of tinnitus. Depending on the loudness of the noise, tinnitus may be fully or partially masked. Tinnitus masking cannot reduce or eliminate tinnitus, only reduce awareness of it. The efficacy of a tinnitus masker may depend on the wearer's capacity to experience residual inhibition, the temporary suppression of tinnitus in response to particular sound patterns. The mechanism of sound masking can be explained by analogy with light. In a dark room where someone is turning a lamp on and off, the light will be obviously noticeable. However, if the overhead lights are turned on, turning on the lamp will no longer be as distracting because it has been "masked". While sound masking is an effective solution for a majority of those with tinnitus, it does not work for everyone.
History The concept that an external sound could suppress perception of an internal one was first realised clinically in the mid-1970s by Dr. Jack Vernon, when he reported that white noise was effective in alleviating tinnitus.
Suppression vs. masking Tinnitus suppression is different from but related to tinnitus masking. It is an acoustic or neurological effect that results in temporary suppression of tinnitus by listening to an appropriately tailored sound for a short period. After the sound is withdrawn, tinnitus may be fully (complete silence) or partially suppressed. Most (70–90%) of persons can experience the effect. There is usually a period of complete silence followed by a gradual return of tinnitus to its original level. The effect lasts for 5 minutes or less in 90% of persons but in rare cases, an hour or more. The period of complete silence is usually seconds to about a minute. If the trigger sound is repeated at intervals, tinnitus can be suppressed as long as the repetition lasts.
Residual inhibition The residual inhibition (RI) effect, first noted in 1903, is the capacity of a sound of the right frequency and intensity to briefly attenuate or suppress tinnitus. To distinguish the tailored sound used for inhibition from the broadband undifferentiated sound employed in tinnitus maskers, it is usually referred to as the 'trigger' or 'quieting' sound. The trigger sound is closely matched to the pitch and spectrum of the tinnitus, and as loud or somewhat louder than the perceived loudness of the tinnitus. The trigger sound is applied to the ear or ears with tinnitus and typically lasts a minute or two. Not everyone can experience RI; for those who do not, tinnitus masking is likely to be ineffective.
Acoustic qualities Two qualities of a tinnitus masker need to be taken into account: how effective the masking is, and how intrusive or distracting the generated sound itself is. The masking sound may have various temporal, spectral and amplitudinal characteristics. In some cases, the sound is tuned to the pitch, loudness and other qualities of the tinnitus. However, frequencies widely divergent from the tinnitus frequency may also mask the tinnitus, if they are of sufficient loudness. The minimum energy (or loudness) mask is usually one closely matched to the central frequency and bandwidth of the tinnitus. But it has also been discovered that a tinnitus mask close to the frequency of the tinnitus can be ineffective, while a masker with a different frequency or bandwidth effectively masks the tinnitus. This indicates different origins of tinnitus. Tinnitus maskers may use music or natural sounds, wide band white or pink noise, narrow band white noise, a notched soundfield, frequency or amplitude modulated sound, intermittent pulsed sound, or other patterned sound. Temporally patterned sound may be more effective than white noise or background music in masking tinnitus. Studies have found that bandpass maskers are less annoying than pure tone maskers, that the annoyance rating of bandpass maskers is proportional to bandwidth, that intermittent maskers were more annoying than continuous ones, and that control over the center frequency and bandwidth was important in minimizing the annoyance of maskers.
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