Click here to purchase the entire book in PDF format. Band-pass Filter Let's take a signal and send it through a high-pass filter and a low-pass filter in series, so the output of one feeds into the input of the other. Let's also assume for a moment that the two cutoff frequencies are more than a decade apart. The result of this probably won't hold any surprises. The high-pass filter will attenuate the low frequencies, allowing the higher frequencies to pass through. The low-pass filter will attenuate the high frequencies, allowing the lower frequencies to pass through. The result is that the high and low frequencies are attenuated, with a middle band (called the passband) that's allowed to pass relatively unaffected. Figure 6.3: The frequency response of a bandpass filter with cutoff frequencies of 100 Hz and 5 kHz.