With filtering out background noise. Their is actually no way to separate background noise from other sound.
What can be filtered out, are specific frequency ranges. With higher frequencies the common ones to be filtered.
But this will filter all higher frequencies, not just those in the background.
Though 7 to 8 years ago, I conducted some research into 'background noise'. With a group of adults and children with APD.
Where my hypothesis was, that a cause of difficulty with background noise?
Is the inability to 'localise sound'. To identify where a sound is coming from?
That hearing can be focused, in a similar way to vision. Which enables us to separate background noise, from what we are trying to listen.
I first tested the group, and found that most were unable to point in the direction of a sound. When their eyes were closed.
For the ones that had this difficulty. I had them do some exercises to help develop this ability.
Which improved for the majority of them.
They then did exercises, where they sat with a TV on one side, and a Radio on the other side.
They then practised, shifting the focus of their hearing, from one to the other.
It had people talking on both sides, so that they tried to follow what was being said on one side. Then to the other side?
Which most of them were able to do, after practising for a while.
With the ones that were successful with this. They then did exercises in noisy environments, such as shopping malls, bars and restaurants. Where they practised focusing their hearing on someone speaking, in this noisy situation?
Previously, this had been impossible for them. But with practice, they found that they were able to follow the conversation. As the background noise, had moved into the background.
But Peter Pans above link to the article: 'Effects of phase difference on the binaural perceiving intensity'.
Directly relates to this. As it shows the practical effect on hearing, when their is a 'phase time delay' with one ear.
How it effects the ability to localise sound.