# Translations:Appendix K: Exercises/64/en

62. Discuss high-pass and low-pass filters. [Answer: The amplitude spectrum of a high-pass (also known as low-cut) filter is nearly flat above a certain cutoff frequency. However, frequencies below the cutoff frequency do not completely disappear in the output. Such frequencies are reduced to a low level. The amplitude spectrum of a low-pass filter (also known as a high-cut filter) is nearly flat below a certain cutoff frequency. Application of this filter greatly reduces all frequencies above the cutoff frequency. Note that a band-pass filter can be obtained as the product of a suitable low-pass filter and a suitable high-pass filter. The amplitude spectrum of a typical notch filter is nearly flat except in a small band or notch in which it approaches zero. There are two parameters: the notch frequency and the width of the notch. A notch filter can suppress power-line interference, such as 50 Hz and its harmonics or 60 Hz and its harmonics.]