What are filters? What are the types of filters?

To determine the type of filter: use Fourier transform to find out H(f), and then draw the amplitude-frequency characteristic curve to see whether the high-frequency part is "through" or not.

There are 0 and 1 times of s in the denominator, and the numerator is 1 time of s, so it is the higher one, referred to as "high times".

H(s)=a/(bs+c) has "lower times" in the numerator, so it's a low pass.

H(s)=as^2/(bs^2+cs+d) has "high times" on the molecule, so it's a high pass.

H(s)=a/(bs^2+cs+d) has a "low order" on the molecule, so it's a low pass.

H(s)=as/(bs^2+cs+d) has "intermediate times" on the molecule, so it's a bandpass.

Main classifications:

There are two types of filters, analog and digital, depending on the signal being processed.

Low-pass filter: it allows the low-frequency or DC component of the signal to pass through and suppresses the high-frequency component or interference and noise;

High-pass filter: it allows the high-frequency component of the signal to pass through and suppresses the low-frequency or DC component;

Band-pass filter: it allows signals of a certain band to pass through, and suppresses signals, interference, and noise that are lower or higher than that band;

Reference to the above: Baidu Encyclopedia-Filter