how do I find the group delay of multirate system.(sample rate converter) , IIR non-linear phase filter
Say decimation by 2 (with lpf) = tf1(num,den)
then again decimation by 2 (with lpf) = tf2(num,den)
In total decimation by 4.
i can do the inidividual stages
gd1 = grpdelay(tf1,fvec,Fs)
gd2 = grpdelay(tf2,fvec,Fs/2)
but how do i find the combined one of the entire system
can two group delays be added ?
Assuming the can be added, is the following scaling inside and outside the grpdelay function correct ?
gd1 = grpdelay(tf1,fvec,Fs)/Fs/2 % converting from samples to seconds
gd2 = grpdelay(tf2,fvec,Fs/2)/Fs/4
Then we can plot it
ylabel('Group Delay (s)');