I have an EEG data with a sampling rate is 500 Hz. Actually, there are too many ways to filter EEG signals. However, the abundance of options is not valid for me. I have to use a causal, linear-phase FIR filter with a small group delay as possible. I also want to -3dB attenuation at cut- off frequencies.
I applied 30th order FIR filter (hamming window 4-30 Hz) on the continuous (non-epoched) EEG. The side-lobe attenuation for higher frequencies is satisfactory but the lower frequency components for this filter failed. I don't want to use rectangular window because of relatively low side-lobe attenuation. How can I design ideal filter to make possible my intention?