There are many factors to how well you hear in noise. Of partial importance is your ability to hear! If you have a hearing loss it means your threshold for sound is increased. You can only hear it when it reaches a certain level, and that level is louder than people with normal hearing. That’s part of it. If you have a conductive loss, it’s the canal, eardrum or middle ear that’s affected. These are mainly responsible for amplifying, and a basic hearing aid can restore this function by raising the volume in the right way. More on hearing loss later.
Assuming the sound is being received by the brain, it then needs to be filtered. If you really “heard” all the sounds in the world it would likely drive you crazy! Have you ever been in a cafe and a young mother is blissfully unaware her child is kicking the table, or his electronic game is shrieking away? She has filtered it out over time, and is genuinely unaware how irritating it is. In a party situation, the hearing system picks up all the sound, and reproduces it as electrical signals. The brain takes the information from both ears and automatically attends to (focuses on) what is important and what can be ignored. You can control a portion of this using your conscious mind...
”er, can you put down that paper and listen to me?!”
... and actually giving your full attention to the person. But the subconscious is responsible for discriminating different sounds, filtering out the unimportant hubbub and allowing you to focus your attention.
With a sensorineural (inner ear) hearing loss, the fidelity of the information coming through to the brain is also impacted. It is best described as a little blurry. It makes it harder to discriminate between the sounds as they arrive at the brain and you find that people with this type of hearing loss benefit much more from higher tech solutions, in anything other than a one to one conversation in a quiet room.
So what do they do? Well the more advanced hearing aids process complex sounds at the source - before they get to your ears let alone your brain. Multiple voices, voices in background noise, voices that are echoing, voices with wind noise in the mics. They “lift and separate” (to use bra terminology!). They not only amplify to your particular frequency requirements, and keep loud/soft balance, but they increase the loudness of a single speaker while simultaneously feeding you a reduced background noise/voice signal.
This magic is created using the polar plot of directional microphones (they can choose where to “look” for sound) and some remarkably sophisticated audio processing.
The more you suffer with NHS aids (or cheaper or badly fitted private aids), the more you have to gain. The higher the Wow Factor. It is a delightful part of my job delivering that Wow Factor and I never get tired of it.