This resistor is very simple. It will have stereo RCA in and out, and 1/8" mini in and out.
All it will do is attenuate 2.5khz by 3 dB, with a Q wide enough to modestly affect frequencies from 1kHz up to 4kHz.
Essentially to mildly scoop out those audio frequencies humans most readily hear. One could plug a line source or phone into it, and RCA out, IE, to a stereo amp. One could use the built- in tone controls('Bass', 'Treble'), to tailor the ends of the bandwidth to taste.
Result? A smoother, less intrusive sound at background or concert- hall levels.
What materials do I need?