Bandpass Filter

Bandpass filters only let frequencies in a certain range pass.

The range of frequencies is called the bandwidth (BW). It goes from low to high -3dB frequencies ($f_L$ to $f_H$), such that

$$\text{BW}=f_H-f_L$$

The center frequency $f_o$ is a geometric mean such that

$$f_o=\sqrt{f_L{f}_H}$$

The quality factor $Q$ is a measure of frequency selectivity

$$Q=\frac{f_o}{\text{BW}}$$

A bandpass filter can easily be made by chaining a Low-pass Filter and Highpass Filter together: