[Pure Tone Hearing Test]What is Pure Tone Masking When does pure tone audiometry need masking?
First, we need to understand:
What is masking?
Masking, in short, is the phenomenon that the intensity of one sound is reduced or disappeared due to the interference of another sound, which is called masking.
For example:
If the same piece of music is played in a simple environment (such as a quiet room), the clarity of the listener will be better; but in a complex environment Down (such as the vegetable market), the clarity of the listener’s listening will be greatly reduced, which is masking.
Second, we need to understand:
Why masking is needed?
In the pure-tone audiometric test, there is sometimes “shadow hearing”: when the hearing thresholds of the two ears are quite different, when the poor ear is tested, the test signal is likely to propagate before reaching its threshold. To the contralateral cochlea, the non-test ear first felt the test sound and responded.
I will show you the following audiograms:
In this audiogram, the hearing thresholds of the left and right ears are quite different, but the overall air conduction test results are very different. near.
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 bad ear), and to obtain the true threshold of the test ear as much as possible. .
Finally, we need to understand:
In pure tone audiometry, what conditions need to be masked?
The commonly used earphones for pure tone audiometers are in-ear earphones, and their interaural attenuation (IA) is between 40 and 70 decibels. Therefore, in the air conduction audiometry, the masking conditions are: the air conduction threshold of the poor ear – the bone conduction threshold of the good ear ≥ 40dB.
For example:
In the audiogram above, at 1000Hz, the left ear air conduction value: 65dB HL, the bone conduction value: 35dB HL; the right ear air conduction value: 35dB HL , Bone conduction value: 25dB HL. At this time, the left ear is the bad ear, and the right ear is the good ear.
The air conduction threshold of the bad 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 of the left ear needs to be masked, and the masking sound is added to the right ear.
