block filters (was Re: [PD] [erratum] question about [lop~] and [hip~])

[julien.breval at tremplin-utc.net]

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