Is AGC Beneficial In Hearing Aids?

Yes, AGC is beneficial in hearing aids because the basic function of a hearing aid is to amplify sound. Whether the goal is simply to restore loudness or to improve speech intelligibility, the gain of most modern hearing aids is nonlinear.

The hearing aid can apply for substantial gain to low-intensity sounds. And less gain to sounds that are already of high intensity.

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The slope of the input/output function of a nonlinear hearing aid is, by definition, less than one. The gain in this example decreases as the input level increases, thus compressing the dynamic range of the sound and presenting to the ear.

Because hearing-impaired listeners often have linear loudness growth and perceive loud sounds normally (known as loudness recruitment). The compressive gain of a hearing aid design to restore nonlinearity by amplifying soft sounds. But minimally affecting more intense sounds.

How Automatic gain control (AGC) benefits hearing aid users?

To automatically control the gain electronically, it detects the incoming sound level and changes the gain accordingly 45. A hearing aid typically splits the signal into at least two frequency bands, detects the incoming level. And applies the appropriate amount of gain.

However, this gain adjustment does not occur instantaneously. Because a single sample does not accurately represent the intensity of the signal, the level must be detected over some time interval. Additionally, it often controls the gain to change somewhat slowly over time and, thus, minimize distortion 82. Fast amplitude modulation can result in spectral components that may not otherwise exist.

When the signal level rises above the threshold, the gain is reduced as a function of time. For fast time constants, the gain is reduced over a short period of time. As implemented in many hearing aids, this time constant is often a few milliseconds. Which corresponds to the approximate length of a syllable.

How much do we gain by automatic gain control in hearing aids?

There are three rationales used for automatic gain control in hearing aids. First among them is to establish loudness relations among the different acoustical elements of speech to what they would be for a normal ear. Right there is a lack in the proof to support the fact that the speech intelligibility gets critically affected by such loudness relations.

The second rationale is to minimize the resulting of the narrowband interfering sounds. This might be applicable in some of the situations not in many others.

The third irrational is one of the most important. Its work is to make sure that all the elements in a speech are comfortably audible. It can be achieved by using two forms of AGC:  slow-acting AGC works on the whole speech signal; from one situation to another to repay for the variations in sound level and fast-acting (syllabic) compression that performs independently in a number of bands, to repay for the variations in the level of acoustical elements of a speech.


The hearing test at RNID has concluded that AGC can benefit hearing aid users in their daily uses. It allows the user to listen to a wider range of sound levels without distortion or discomfort.

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