# Filters what are they?

1. Aug 23, 2009

### blackout77

Filters what are they??

Can someone explain to me what are filters (DSP) in plain english? Fir filter, IIR filter,... Chebyshev, Butterworth,... Bands (stop, pass, lowpass, highpass).

2. Aug 23, 2009

### negitron

Re: Filters what are they??

http://www.dspguru.com/info/terms/filtterm/index.htm [Broken]

Last edited by a moderator: May 4, 2017
3. Aug 23, 2009

### chroot

Staff Emeritus
Re: Filters what are they??

Is this homework?

- Warren

4. Aug 23, 2009

### blackout77

Re: Filters what are they??

Nope, I just couldn't find a good explanation of what they are without getting into so much technicality.

5. Aug 23, 2009

### abros

Re: Filters what are they??

Every signal can be described as a sum of sinusoids with different frequencies. Simply put, filters can block certain frequencies in your signal. So for example, a low pass filter would block out the high frequency components of the signal.

6. Aug 24, 2009

### chroot

Staff Emeritus
Re: Filters what are they??

A "band" is a range of frequencies.

A lowpass filter passes all signal components with less than some critical frequency, called the cutoff frequency.

A highpass filter passes all signal components with greater than some cutoff frequency.

A bandpass filter passes only signal components within some band.

A stopband filter stops only signal components within some band.

FIR filters have a finite-duration impulse response. If you put an impulse (a signal that is zero everywhere except a very brief interval of time) into an FIR filter, the response will eventually die down to zero and stay there forever.

IIR filters have (potentially) infinite-duration impulse response. The output of an unstable IIR filter will oscillate forever in response to an impulse.

A Butterworth filter is a monotonically-decreasing filter with maximal passband flatness. Its frequency response gently decreases in amplitude with increasing frequency. It is a very easy-to-understand filter.

A Chebyshev filter is not monotonically-decreasing, and trades flatness in either the passband or stopband for a narrower transition between passband and stopband.

- Warren