Why condition of linear phase is important in filters?

[wajahat]

If phase of a filter is linear than no distortion would occur in the o/p signal,HOW?

 

[teteamigo]

Band Pass filter: Constant gain, phase linear with w.


Phase no linear implies signal distortion (linear), group delay isn't constant with w.

 

[e_arbiter]

for this you need to understand what liner phase means.
In general linear phase is used if you want to modify only the amplitude of the signal without any other kind of change..

Here's the reference you are seeking
https://ccrma.stanford.edu/~jos/filters/Filters_Preserving_Phase.html

 

[Kral]

wajahat,
In general, phase linearity is a parameter that is defined for the passband of a filter. If the phase shift of a filter is linear with respect to frequency, then every frequency component of the signal will be delayed by an equal amount. The result is an output signal that is delayed, but not distorted. Group delay is defined as the neagative slope of the phase with respect to frequency. If the group delay is constant, tis implies phase linearity.
Regards,
Kral