First, we must determine what the person considers ''noise.'' For some people it's the refrigerator, for others it's traffic, for some it's new environmental sounds, and for many it's simply background speech that they don't want to hear.
Most of today's hearing aids have several features to address all the different types of noise. Let's first talk about the low-level noise that is constantly present all around us. One of the goals of most hearing aid fittings is to make soft speech audible. But, we do not want to apply the same amount of amplification to sounds below the level of soft speech. If we did, ambient environmental sounds would be unusually loud for the hearing aid wearer. So a Hearing Care Professional reduces the energy of the signal of low-level sounds. It works quite well, and in fact, the result is that some hearing aids are so quiet in a quiet room that the wearer thinks that they aren't even turned on!
For noise above the level of soft speech, the primary noise reduction technique used is digital noise reduction (DNR). If the primary signal is noise, the DNR will reduce the hearing aid's energy. Importantly, this feature works independently in several different channels, so noise centered in the low frequencies (pitches) will not reduce the energy in the high frequencies. Again, this features works well, and several studies have shown that wearers find noise to be ''less annoying'' when this feature is activated, and they usually prefer this setting for ''listening comfort.''
If the ''noise'' is really background speech, or noise that has more ''speech-like'' characteristics, then DNR may not have a significant effect. In this listening situation, the preferred noise reduction technique is directional microphone technology. Assuming that the hearing aid wearer can position himself so the signal of interest is in front, and the ''noise'' is from the sides and behind, this strategy is very helpful in reducing annoying noise, and improving speech understanding. Some directional products are now ''automatic'' and ''adaptive'' which adds to the effectiveness of the noise reduction for some listening environments.
So, in summary, we have three different features which all work together to assist in reducing annoying background ''noise.'' With today's hearing instruments, improved speech understanding and less disturbance from background noise should be the result.