Minimum masking level (MML): the loudness needed to cover your tinnitus

What the minimum masking level measures

The minimum masking level (MML) is a psychoacoustic measurement that identifies the lowest level of broadband noise, usually white or wideband noise, at which tinnitus becomes inaudible. It is expressed in decibels sensation level (dB SL), meaning the number of decibels above the person’s audiometric hearing threshold at the test frequency or across the test band.

MML is part of a broader psychoacoustic tinnitus assessment that typically also includes tinnitus pitch matching (identifying the frequency that best corresponds to the perceived pitch of the tinnitus) and tinnitus loudness matching (identifying the level at which an external tone sounds as loud as the tinnitus). Together, these measures build a quantitative profile of the tinnitus as a sound.

Why MML is clinically useful

MML has two main clinical applications: characterizing the tinnitus for assessment purposes, and providing a practical basis for sound therapy approaches.

For assessment, the MML tells the clinician how much external sound energy is needed to suppress the tinnitus signal. A low MML (sometimes just a few dB above threshold) means relatively quiet environmental sounds can cover the tinnitus; a high MML indicates the tinnitus is more resistant to masking. This information can inform the sound levels used in sound therapy and may guide which sound therapy approach is most appropriate.

For sound therapy planning, MML establishes a practical floor. Sound enrichment, one element of tinnitus management approaches such as tinnitus retraining therapy, uses low-level background sound delivered at or below the MML to reduce the contrast between the tinnitus and the acoustic environment. The NIDCD notes that sound therapies are commonly used as part of tinnitus management, though evidence levels vary across specific approaches.

How the test is performed

The audiologist seats the patient in a sound-treated room and presents broadband noise through earphones or a loudspeaker at a level that is clearly below the tinnitus. The noise level is then raised in small steps, typically one decibel at a time, while the patient monitors their tinnitus. The test continues until the patient reports that the tinnitus has just become inaudible. That level, minus the hearing threshold, is the MML in dB SL.

Some protocols present the noise to the ear in which tinnitus is most prominent; others use bilateral presentation. Some use noise bands centered on the tinnitus pitch rather than broadband noise. The exact method affects the result, so clinical MML values should be interpreted in the context of the protocol used to obtain them.

The test requires good cooperation from the patient: the ability to attend to a fluctuating internal percept while listening for changes, and the ability to reliably indicate when the tinnitus disappears. This is subjectively demanding, and variability between test sessions is known to occur.

MML versus loudness discomfort level

MML and loudness discomfort level (LDL) are sometimes measured in the same session because both use controlled sound delivery through earphones, but they measure different things. MML identifies the level needed to suppress tinnitus. LDL identifies the level at which sound becomes uncomfortably loud. Together they define two important boundaries: the practical noise range for sound therapy (above MML to be effective) and the upper limit of comfortable loudness (below LDL to be tolerable).

For people with hyperacusis, a heightened sensitivity to ordinary sounds, LDL values can be low, meaning the tolerable range between the background and the discomfort level is narrow. In these cases, MML may exceed the comfortable dynamic range, making traditional masking-level-based sound therapy impractical without modification.

MML and residual inhibition

Residual inhibition is a related phenomenon: after the masking noise is turned off, tinnitus is temporarily suppressed or reduced in a substantial proportion of people. The duration and degree of residual inhibition vary widely. MML assessment sometimes includes observation of residual inhibition after the masking noise stops, because the presence and duration of residual inhibition may have implications for certain sound-based interventions.

The British Tinnitus Association describes residual inhibition as one of several psychoacoustic phenomena that researchers use to understand tinnitus mechanisms and explore potential therapeutic approaches.

What MML does not measure

MML is a measure of one acoustic property of tinnitus, not a measure of distress or disability. Decades of tinnitus research have consistently shown that the loudness and maskability of tinnitus correlate poorly with how much distress it causes. Many people with very low MML values, meaning their tinnitus is easily masked, experience severe functional and emotional impact. Others with higher MML values live with their tinnitus with relatively little disruption.

Distress, functional impact, and quality-of-life measures require questionnaire-based assessment, such as the Tinnitus Handicap Inventory, rather than acoustic measurement.

If symptoms persist or change, see an audiologist or physician.