phase delays and group delays

[kingmakerbull]

Can someone explain me the physical meaning of group and phase delay in FIR filters? I know the formulae but cant get to grasp the significance

 

[Kral]

kingmakerbull,
Group delay is the derivative (slope) of phase with respect to frequency at a given frequency. Phase delay is phase divided by frequency at a given frequency. If the filter is of the linear phase type, then the curve of phase versus frequency is linear, and the group and phase delays will be identical. Group delay for a linear phase filter is the actual time telay from input to output of signal.
Regards,
Kral

 

[mowgli]

As already written by Kral the group delay is the rate of variation of the phase wrt the frequency: if this rate is not constant (= is a function of the frequency) the consequence will be that the different harmonic components of the signal will experience different phase increments while travelling through the same medium, therefore a distortion at the output will arise, because the relative phases of the output components are not the same as at the input.

Regards

Mowgli

 

[zorro]

Imagine a sinusoidal signal with a slow amplitude modulation, "slow" meaning that the frequency of the amplitude variations is very low compared with the frequency of the sinusoid.
Pass this signal by a network (for instance, a filter).
At the output, you see that:
a) the sinusoid is delayed with respect to the input. This is the phase delay
b) the amplitude variations are delayed with respect to the variations at the input. This is the group delay.
Regards

Z