These techniques make hearing aids better understand you.
Volume adjustment is a basic function of hearing aids. Adjusting the volume is actually adjusting the gain. With the continuous development of digital hearing aids, the gain adjustment has also been amplified or reduced from a single overall, and gradually evolved into multi-band, multi-channel independent adjustment. Why does the fitter adjust the gain in sub-bands? Which technology depends on the hearing aid?
The gain adjustment function mainly relies on the filter’s management of the frequency response. According to the frequency adjustment range, the filter can be divided into the following three types:
1, high pass filter
Allows high frequency sound to pass, providing more gain for high frequency sound.
2, bandpass filter
Allows sound in a certain band to pass, providing more gain for sound in that band.
3, low pass filter
Allow low frequency sound to pass, providing more gain for low frequency sound.
Analog hearing aids and simple digital hearing aids usually use only one type of filter, while more complex digital hearing aids use both high-frequency filters and low-frequency filters to achieve both speech and noise management.
The greater the number of filters used, the more channels and bands that can be independently adjusted, which is why the fitter can make a “personalized” adjustment based on the gain requirements of the user’s various frequencies.
In addition to the above classification, the filter can be divided into three other types according to the complexity of the internal technology: passive filter, active filter and switched-capacitor filter. ).
1, passive filter
Passive filter is the simplest structure of a filter. It consists of only resistors and capacitors. It does not consume power when working. However, passive filters can only attenuate low-frequency information of about 6dB, and cannot provide more “noise reduction”. “.
In Figure (a), when the passive filter attenuates the low-frequency information too much (attenuation reaches 12dB), the original high-frequency gain curve will be moved, which will affect the accuracy of the sound quality and gain adjustment.
2, active filter
The active filter combines an amplifier based on a passive filter. Although it consumes a part of the power during operation, the active filter can increase the attenuation of low-frequency information and provide a wider frequency response over a specified frequency range. In Figure (b), when the active filter also attenuates the low frequency information of 12dB, the active filter does not move the original high frequency gain curve, thereby achieving more “noise reduction”.
3, switched capacitor filter
Switched capacitive filters are also a filtering technique applied to digital hearing aids.
It can combine the sampling information of the analog-to-digital converter for more complex digital operations to achieve a more complex frequency response. However, the stability of such filters is generally poor, so the current application is not extensive. The filter is the core to achieve independent adjustment of the gain and is the basis for sound attenuation.
On the one hand, the combination of a low-pass filter and a high-pass filter allows the hearing aid to meet the user’s “personalized” gain requirements for each frequency band to the utmost extent. On the other hand, the attenuation of low frequency information by active and passive filters also contributes to “noise reduction”.
Therefore, the filter is undoubtedly the core component to meet the individual needs of users.
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