Hi, totally get you here as myself searching for same solution when HP filter is in lowest state (20hz) it being bypassed and as soon it get to 21hz it got engaged(without clicks and pops) and starts working and when it’s back to 20hz it being bypassed and restores original phase. Unfortunately this isn’t quite easy to achieve since there are not anything intuitive on the market that will turn off filter when it’s “done” and I would skip Lin phase cause it’s introducing lot of pre ringing (especially above 12db per octave) and latency is second main issue. As technical paranoid myself for low end and theirs phase coherence I assume you are mostly in electronic music genres like myself. I found several options:
- Using xfer djm filter which I suppose it basically bypass filter when it’s on middle (i tried it long time ago but cannot remember correctly)
- Using pro q but manually bypassing it when it’s not “working” -be careful this can introduced some pops when automating bypass so you have to find sweet spot where it turns on/off, also you may adjust timing of automation since pro q has smooth interpolation (in practice it’s not that fast and you have sense it’s lagging especially on fast kinda ramp automations)
- The Best solution i found is in Melda plugins where in their modular MXXX i program unit which will do exactly i described above (turn off HP filter when it’s on 20hz, as well LP filter when it’s on 20khz) and the best thing is that you can go pretty detailed and technical, it has smooth bypass option where I achieved basically no pops/clicks in practice and the best thing automations are fast without smoothing (apart you can set that as well) so for example when you automate volume and it goes straight from 100 to 0(ramp) it doesn’t slips any fade out signal but the “mute” effect is instant. You can try Mbandpass(free) which i used in MXXX.
More on topic here: Filter automation is too low rate
Cheers