Stereo bandpass filter

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Hi,

I am trying to tune my car and made an adapter cable from the factory knock sensor to a small stereo jack.

I sounds good but i would like to interfere a bandpass filter so i only hear the frequency i am interested in (in this example 6900-7200 Hz).

Can someone help me out here since circuit design is not my field? :)

I would not mind if it would also amplify the signal and gave me earphone output. (if there is a ready cheap solution, let me know).

thanks
 
lets say from 0 to 6800 and from 7200 - 40000 the less the better.

The frequency under 6800 and above 7200 is not of importance. Center should be 7000hz.

The expensive devices that meant to do this job are using "passive noise canceling".....whatever that means.
 
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