[music-dsp] Changing roll-off slope of Bi-Quad filter

Nigel Redmon earlevel at earlevel.com
Mon Oct 4 21:27:56 EDT 2010


Hi Kevin,

Quick answer off the top of my head, but... You get 6 db/oct per order for a single-corner filter (lowpass, highpass...), so 12 db/oct for a bi-quad. It you want to want to make a variable slope (that is, continuously variable and not just in 6 dB/oct increments), you'll have to spread out the poles to approximate the slope you want (there will be some ripple, dependent on the number of poles.

Nigel


On Oct 4, 2010, at 2:05 AM, Kevin Dixon wrote:
> I feel like this must have been asked before, but I couldn't find it
> on the archives. I was wondering what sort of adjustments need to be
> made to support variable roll-off. After measuring the frequency
> response of the filters in the audio-eq-cookbook (thanks rbj!), I see
> they have a 6dB per octave slope. If I want to show an option to my
> users, for example 6, 12, 24 and maybe 32, what is the best approach
> to take here? Thanks!
> 
> -Kevin



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