FabFilter User Forum

What exactly is Pro-Q3 Brickwall doing?

Can Fabfilter provide a bit more detail on exactly what the new Brickwall filter mode is doing? Is it like other slopes except even more extreme, or is there any other special logic (Chebychev, Cauer, etc.) that the Brickwall slope uses to avoid negative aspects of such a steep slope?

Thanks for your time and help.


Hi Beaker,

The Brickwall filter is an elliptic filter of a very high order, which results in an extremely steep slope, while still introducing the same, or even less phase distortion as the 96dB/oct Butterworth filter. It does introduce a little bit of ripple in the pass band, but that's hardly noticeable... As for the negative effect: it will still introduce quite some phase changes, but as always the best thing is to just judge with your ears :-)

Floris (FabFilter)

Thank you for these details. :)


You're specifying it will change the phase.. will a linear phase set on maximum eliminate this?
And the ringing is at the frequency you cut?
Also how does it compare to izotope's brickwall? ( in neutrin,ozone,alloy) ?
Because there then you brickwall you can sometimes hear massive ringing(although on most sources it does not happen)



Hi Alon,

There's no ringing, but a very small ripple (around 0.05 dB) in the pass band. And yes, you can eliminate the phase by putting Pro-Q 3 in linear phase mode, but do keep in mind that this will introduce significant pre-ring for Low-Cut filters due to the steep filtering. More about this here:


Frederik (FabFilter)

Just passing by to say thanks for the explanations, highly helpful


Yeah this was awesome, thank you!

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