Filterband

Filterband is a term used in signal processing to describe the frequency range that a filter passes with minimal attenuation, or more generally the passbands defined by the filters in a filter bank. A filter’s band is characterized by its center frequency and its bandwidth, which determine which components of a signal are transmitted and which are attenuated. The passband is the portion of the spectrum where the filter’s gain is at or near a specified level, while the stopband lies outside this range where signals are attenuated.

In a filter bank, several filters operate in parallel to partition a signal into multiple filterbands. Each branch passes a different portion of the spectrum, allowing simultaneous analysis, processing, or transmission of distinct frequency ranges. Filterbanks are used in applications such as subband coding, graphic equalization, radio receivers, and multi-channel audio systems. The design of a filterband involves choosing the center frequency, bandwidth, and the acceptable levels of ripple in the passband and attenuation in the stopband. The quality factor, Q = center frequency divided by bandwidth, is a common measure of how narrow or selective a filterband is.

Implementation can be analog or digital. Analog filterbands are realized with passive or active networks, ferrite or SAW filters, or other RF components. Digital filterbands are implemented with finite impulse response (FIR) or infinite impulse response (IIR) filters, often arranged in polyphase structures or through FFT-based methods in multirate systems.

See also: bandpass filter, filter bank, bandwidth, Nyquist frequency, Q factor.