Abstract: Pure-tone hearing test is a commonly used audiological examination method in our clinical practice. The accuracy of pure-tone hearing test often affects the effect of hearing aid fitting for users. Masking is a difficult point in pure tone audiometry. Let me first explain to you when masking is needed. Pure-tone audiometry What is pure-tone masking? When does pure-tone audiometry require masking?

First, we need to understand:

What is masking?

Masking, in short, is the phenomenon in which the intensity of a sound perceived by the human ear is weakened or disappears due to interference from another sound, which is called masking.

For example:

When the same piece of music is played in a simple environment (such as a quiet room), the listener will hear the clarity better; but in a complex environment (such as a wet market), the listener's hearing clarity will be greatly reduced, which is masking.

Secondly, we need to understand:

Why is masking needed?

In pure tone hearing tests, there is sometimes "shadow hearing": when the hearing thresholds of the two ears are very different, when the difference ear is tested, the test signal is likely to be transmitted to the contralateral cochlea before reaching its threshold. , the non-test ear senses the test sound first and responds.

Use a specific audiogram to show you:

In this audiogram, the hearing thresholds of the left and right ears are quite different, but the trends in the overall air conduction test results are very similar.

Therefore, the purpose of masking in the pure tone hearing threshold test is to avoid the participation of the non-test ear (that is, the good ear "overhears" the signal sound played at the poor ear), and to obtain the true threshold of the test ear as much as possible .

Finally, we need to understand:

What are the conditions for masking in pure tone audiometry?

The commonly used headphones for pure tone audiometers are in-ear headphones, whose interaural attenuation value (IA) is between 40 and 70 decibels. Therefore, in air conduction audiometry, the masking condition is: air conduction threshold of the poor ear - bone conduction threshold of the good ear ≥ 40dB.

Example:

In the audiogram above, at 1000Hz, the air conductance value of the left ear: 65dBHL, bone conduction value: 35dBHL; the air conductance value of the right ear: 35dBHL, bone conduction Value: 25dBHL. At this time, the left ear is the bad ear and the right ear is the good ear.

The air conduction threshold of the poor ear (65) - the bone conduction threshold of the good ear (25) = 40dB, which meets the conditions. At this time, the air conduction hearing threshold test at 1000Hz in the left ear requires masking, and the masking sound is added to the right ear.