Hearing Aids that Block Background Noise - We Call these Hearing Aids with Directional Mics.
Most older hearing aids have only an omnidirectional microphone. An omnidirectional microphone amplifies sounds equally from all directions. In contrast, a directional microphone amplifies sounds from in front more than sounds from other directions. This means that sounds originating from the direction the listener is facing are amplified more than sounds from behind or in other directions. If the speech is in front of the listener and the noise is from a different direction, then compared to an omnidirectional microphone, a directional microphone provides a better signal to noise ratio. Improving the signal to noise ratio improves speech understanding in noise. Directional microphones is one of the best methods to improve the signal to noise ratio.
Some new hearing aids now have both an omnidirectional and a directional microphone. This is because speech often comes from directions other than in front of the listener. Usually, the omnidirectional microphone mode is used in quiet listening situations (e.g. living room) whereas the directional microphone is used in noisy listening situations (e.g. restaurant). The microphone mode is typically selected by using a switch. Some hearing aids automatically switch the microphone mode.
Adaptive directional microphones vary the direction of maximum amplification. The direction of amplification is varied by the hearing aid processor. The processor attempts to provide maximum amplification in the direction of the speech signal. Unless the user manually temporarily switches to a "restaurant program, forward only mode" adaptive directional microphones have a disadvantage of amplifying speech of other talkers in a restaurant. This makes it difficult for the processor to select the desired speech signal. Another disadvantage is that noise often mimics speech characteristics, making it difficult to separate the speech from the noise. Despite the disadvantages, adaptive directional microphones can provide improved speech recognition in noise. Directional microphones only provide benefit when the distance to the talker is small.