As a design input for an low-pass FIR filter I have 6dB@1.6kHz, 24 dB/oct, sample frequency 48kHz. I need to specify phase response, and for that I need a phase slope. I have found, from Julius O. Smith web page, that the phase slope = (N-1)/2 where N is number of taps. What is the way to determine the optimal number of taps? I am aware of Kaiser formula, but I don't have ripple, passband and stopband frequencies that figure in the formula. I need the number of taps to calculate phase slope. Is there any other way to calculate, specify phase from my input requirements?