PGRPDELAY - Group delay of a filter with periodic boundaries

Usage

ggd = pgrpdelay(g,L);

Description

pgrpdelay(g,L) computes group delay of filter g as a negative derivative of the phase frequency response of filter g assuming periodic (cyclic) boundaries i.e. the delay may be a negative number. The derivative is calculated using the second order centered difference approximation. The resulting group delay is in samples.

Example:

The following example shows a group delay of causal, moving average 6tap FIR filter and it's magnitude frequency response for comparison. The dips in the group delay correspond to places where modulus of the frequency response falls to zero.:

g = struct(struct('h',ones(6,1),'offset',0));
L = 512;
figure(1);
subplot(2,1,1);
plot(-L/2+1:L/2,fftshift(pgrpdelay(g,512)));
axis tight;ylim([0,4]);

subplot(2,1,2);
magresp(g,L,'nf');