A high-pass filter, or low-cut filter, attenuates everything below a cutoff frequency. With a cutoff of 80 Hz and a slope of 18 dB per octave, for instance, a signal is reduced by 18 dB at 40 Hz and by 36 dB at 20 Hz. Engineers use it routinely to clear away microphone rumble and subsonic noise, so that the kick drum and bass have room in the mix.
Used more heavily, a high-pass filter makes a sound small and thin, like music from a tiny radio or an old record player. Adam Scott Neal’s analysis of lo-fi hip hop describes producers using exactly this trick to evoke an old record or radio, and combining it with a low-pass filter leaves only a narrow band of midrange, a quick route to a vintage telephone-like tone.