Linear phase
From Wikipedia, the free encyclopedia
Linear phase is a property of a filter, where the phase response of the filter is a linear function of frequency, excluding the possibility of wraps at 
. In a causal system, perfect linear phase can be achieved with a discrete-time FIR filter.
Since a linear phase (or generalized linear phase) filter has constant group delay, all frequency components have equal delay times. That is, there is no distortion due of select frequencies; in many applications, this constant group delay is advantageous. By contrast, a filter with non-linear phase has a group delay that varies with frequency, resulting in phase distortion.
Some examples of linear and non-linear phase filters are given below. 
