The function of the trimming controller is to adjust the parameters of the amplifier so that the final output sound matches the hearing loss of each hearing-impaired person. It includes switches, volume controls, various fine-tuning and more. The controller can be a mechanical potentiometer or a register, and the parameters can be adjusted by a computer.

1) Switch

Traditional behind-the-ear and box-type hearing aids generally use “OTM” switches, and the switch and volume control of the custom machine are integrated. The “OTM” switch of the behind-the-ear hearing aid is very susceptible to moisture and can cause the whole machine to malfunction. Therefore, the new design uses a battery door as the switch

2) volume control

The volume control allows the user to adjust the volume by himself. The volume adjustment range of some digital hearing aids can be set by software, and the fitter can set a suitable adjustment range for the user.

3) fine-tuning

The trimmer potentiometer is used to adjust the output signal of the hearing aid, and is usually set by the fitting engineer according to the hearing loss of the hearing impaired. There are many types of trimming. The most common is the frequency response regulator. The frequency characteristics of hearing aids are determined by filters. The filtering characteristics are related to resistance and capacitance. In order to change the frequency response of hearing aids, a small variable potentiometer is used to adjust Generally, the effect of increasing high frequency is achieved by attenuating a part of low frequency components (such as NH trimming), and the effect of increasing low frequency is achieved by attenuating part of high frequency components (such as NL trimming).

① NH-low frequency control: The function of increasing high frequency is achieved by attenuating a part of low frequency components, and its main effect is the reduction of low frequency noise.

② NL-high-frequency regulation: By attenuating a part of high-frequency components to achieve the effect of improving low-frequency, its main effects are the improvement of speech intelligibility and the elimination of acoustic feedback.

③ MPO-Maximum Output Limit: In order to prevent the sound output from exceeding the discomfort threshold of hearing impaired people, most hearing aids have a maximum sound output limiting device, such as Peak clipping (PC), automatic gain control of the circuit (automatic gain control) , AGC) circuit and so on. The peak clipping circuit is to remove the peak portion of a signal that exceeds a certain limit, but the output band is distorted after the peak clipping, and the signal-to-noise ratio is small. The AGC circuit is a more advanced limiting control circuit. It compresses the output sound that is greater than the uncomfortable threshold and outputs it, so it will not bring distortion, but the compression is time-dependent. For particularly sensitive patients, peak clipping is sometimes used. safer.

④TK-Compression inflection point / CR–Compression ratio: It is a unique fine adjustment of compression line. Automatic gain compression control (AGC) is a feedback device that automatically reduces the gain of the hearing aid without causing distortion, thereby limiting the hearing aid output. Once the automatic gain compression control works, a new linear relationship is established between the input and output. The compression inflection point is the minimum input sound pressure level required for compression to take effect. The higher the inflection point is set, the greater the hearing aid gain; the compression ratio is the ratio of the input change to the output change after compression is started. A large value indicates a smaller gain. When the compression ratio is equal to 1: 1, it indicates linear amplification.

⑤ Gain control (GC) and VC are used to adjust the main voice gain of the whole band. The wearer feels the change in the overall loudness. Generally, the adjustment range of VC is smaller than GC.


Junious Luo  /Senior Sales

Huizhou Jinghao Medical Technology Co.,Ltd

Mob/whatsapp/Wechat: +15017913539




FL6, Huicheng Industry Bld, Zhongkai High-tech Zone, Huizhou, 516006, Guangdong, China

Link:The role and debugging of hearing aid trimming controller

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