signal processing - low pass FIR filter - with no latency -

i'm using fir filter oversample audio. it's simple typical windowed sinc, i.e. sinc function truncated , windowed. usual requires past , 'future' samples work. in practical terms means audio output delayed. sinc function ideal low pass filter. question equivalent, except no 'future' samples required. guess function same impulse response of brick wall iir filter. have perfect brick-wall cuttoff, not have perfect phase response.

if want particular frequency response, minimum phase filter provide lowest "delay" or latency of iir or fir filter response. iir filter poles , zeros inside unit circle minimum phase filter. minimum phase filter not linear phase, you'll have release constraint reduce latency. fir filter can approximately converted minimum phase either cepstum techniques (see oppenheim & schafer), or numerically solving iir filter similar enough frequency response, flipping poles , zeros inside, , converting suitably windowed impulse response fir filter.

trying less minimum phase delay flatten filter's transition band(s) until, @ "zero" delay, filter either have reject nothing or reject everything, , become useless.