Filter options:
-k keep ALL frequencies (disables all filters),
Can cause ringing and twinkling
--lowpass frequency(kHz), lowpass filter cutoff above freq
--lowpass-width frequency(kHz) - default 15% of lowpass freq
--highpass frequency(kHz), highpass filter cutoff below freq
--highpass-width frequency(kHz) - default 15% of highpass freq
具体没研究过。懒的话直接-k就是了