High-pass filter
= High-pass filter
{title2=$H(s)=s\tau/(1+s\tau)$ for a first-order RC example}
A <high-pass filter> attenuates low <frequencies> relative to a specified higher-frequency pass-band. A simple first-order RC high-pass has the displayed <transfer function>, with a zero at zero <frequency> and a <pole> at $s=-1/\tau$. Combining a high-pass with a low-pass makes a band-pass, but its attainable selectivity depends on <pole> structure rather than gain alone.