The transition band, also called the skirt, is a range of

frequencies Frequency is the number of occurrences of a repeating event per unit of time. It is also occasionally referred to as ''temporal frequency'' for clarity, and is distinct from ''angular frequency''. Frequency is measured in hertz (Hz) which is eq ...

that allows a transition between a

passband A passband is the range of frequencies or wavelengths that can pass through a filter. For example, a radio receiver contains a bandpass filter to select the frequency of the desired radio signal out of all the radio waves picked up by its antenn ...

and a stopband of a

signal processing filter In signal processing, a filter is a device or process that removes some unwanted components or features from a signal. Filtering is a class of signal processing, the defining feature of filters being the complete or partial suppression of some aspe ...

. The transition band is defined by a passband and a stopband

cutoff frequency In physics and electrical engineering, a cutoff frequency, corner frequency, or break frequency is a boundary in a system's frequency response at which energy flowing through the system begins to be reduced ( attenuated or reflected) rather than ...

or corner frequency. This is the area between where a filter "turns the corner" and where it "hits the bottom". An example of this can be taken from a

low-pass filter A low-pass filter is a filter that passes signals with a frequency lower than a selected cutoff frequency and attenuates signals with frequencies higher than the cutoff frequency. The exact frequency response of the filter depends on the filter des ...

, commonly used in audio systems to allow the bass signal to pass through to a

subwoofer A subwoofer (or sub) is a loudspeaker designed to reproduce low-pitched audio frequencies known as bass and sub-bass, lower in frequency than those which can be (optimally) generated by a woofer. The typical frequency range for a subwoofer i ...

, and cut out all unwanted frequencies above a defined point. If the cutoff point for such a filter is defined as 200 Hz, then in a perfect system, all frequencies above 200 Hz will be stopped and all frequencies below 200 Hz will be allowed to pass through. The transition band can be implemented to allow for a smooth fall off to avoid introducing audible peaks in amplitude. If the transition band of the example 200 Hz filter is 20 Hz, then the signal should start attenuating at 180 Hz, and finally blocked at 200 Hz. The curve that the transition band follows depends on the engineering of the filter, including component reaction time and the choice of values for the components that comprise the filter according to mathematical formula. The transition band is usually apparent in any filter system, even if it is unwanted. This can be of general importance when calculating the values required for filters used in the control of signal transmission systems, to ensure that the entire bandwidth of the desired signal is allowed to pass. The transition bandwidth of a filter largely depends on the order of the filter. For a higher order filter, the transition bandwidth is narrower than for a lower order filter. This is due to the fact that

roll-off Roll-off is the steepness of a Transfer function, transfer function with frequency, particularly in network analysis (electrical circuits), electrical network analysis, and most especially in connection with filter (signal processing), filter cir ...

is higher for a filter of higher order.

References

{{DEFAULTSORT:Transition Band Filter frequency response

See also

References