Hello
For true brick shape, use series higher order filters. The full iemabs lib has 2nd through 10th order butterworth and other filters available. Make your cutoff frequencies track as well.
[r audio] | | [r cf] | [/ 1.2 ] | | [hp10_butt~] | | [r cf] | [* 1.2] | | [lp10_butt~]
that's very similar to what I did (the only difference is that I used 2 independant cutoffs), but I can't change the "cf" fast enough (on my computer, the iem filters make an digital artefact noise when changing the cutoff too fast, which means under 30 ms -- and maybe it's completely normal). By the way the original [hip~] have similar problems (whereas [lop~] can have its cutoff changed very fast without making any noise, even if you jump from 30 Hz to 20000 Hz in 1 ms).
The only solution I have found is to use a series of this block filter (3 or 5), to change their frequencies very sporadically (as a manual parameter, for example), and to make the signal pass in the filter I want. It's not very good for saving CPU load, but it's the only solution that works perfectly at high speeds.
THanks for your help