Compensating for group delay in FIR with symmetrical coefficients Suppose I have a sinusoidal signal of 50Hz sampled at 6.4kHz and I wished to filter it at:

Band pass: 160Hz, Bands stop: 800Hz, Apass:0.1db, Astop: 106db

For a FIR filter order of 40 I would get 41 number of taps. The group delay would thus be (41-1)/2 = 20.

Am i wrong in thinking that if I extended (/zero padded at the end of) the data block size to be filtered by the estimated group delay above, I would be compensating for the group delay?

For example if I had 128 samples (corresponds to a full sine cycle at 50Hz-Fs=6.4Khz) to be filtered and added the group delay 128+20=148. Now, if I were to filter these 148 samples with the above stated filter, would I not get a signal with no group delay?

Thanks
Alex
No.

There is no way you can compensate for a  broad-band group delay without violating causality. If you add zeros at the end of your signal, the group delay stays constant and if you add zeros in front of it, the group delay goes up.

At some frequencies it may look that there is no group delay (or phase shift), but that's just an illusion: the phase of the filter at this frequency just happens to be an integer multiple of two pi. If you look at any other frequency, it won't be true any more.