block filters (was Re: [PD] [erratum] question about [lop~] and [hip~])
julien.breval at tremplin-utc.net
julien.breval at tremplin-utc.net
Sat Oct 9 14:20:22 CEST 2004
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
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