Project Help Needed... About sound process..

dear friends
i want to filter sound frequences real time and send unfiltered area to earphone .
For ex with pot i want to set 7khz to 15 khz .And just arduino will send sound between this two frrequenc to earphone.
Where i have to start?
And any other similar project anyone knows?

You don't need a processor for that. You can do it with simple components, your pot, some capacitors, maybe a few resistors.

If you tried to make Arduino do it digitally the sample rate would be really slow and it wouldn't sound very good at all.

Google "band pass filter circuit"

I’d look at a pi for that job if you want to do clever digital