I found it very difficult to find a good setting for the NB
any tip?

It really depends on the type of Noise you have

Here I get a lot of powerline noise and depending on the band in which I am using and mode at the time

I found that generally lowing the Threshold of NB1 to around 1.99-2.30 generally works well

as for NB2 I use 2.225 up to the default setting

Is there a in general type of noise yo have.

If it coming from your power supply or something very close ( crappy wall wart) or LED lighting you will need to take other steps-