see
https://www.masteringthemix.com/blogs/learn/what-eq-filter-is-best-for-bass-and-low-end
https://ffmpeg.org/ffmpeg-all.html#firequalizer
for boosting low frequencies
the current linear-phase might introduce audiable ringing temperal artifacts
add option for minimum-phase version
and possibly also intermediate (adjustable) phase
All filters introduce some ringing, though some filters ring more than others. Filter design is a matter of compromise between different characteristics, commonly trading between performance in the frequency domain against performance in the time domain. Audacity provides a selection of filters, including the FFT “Equalizaion” filter, the biquad “High Pass” and “Low Pass” filters, and the “Classic Filters” (not enabled by default, but may be enabled in the plug-in manager).
Additional filter types may be installed as plug-ins.