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Tag Archives: Nyquist EQ

IIR based EQ and distortions

“IIR” stands for Infinite Impulse Response. This is one of possible ways to implement digital EQ. This way is very CPU lightweight. But it’s impossible to make linear-phase EQ using IIR. So the most digital min-phase equalizers are IIR.

Let’s get cookbook peaking filter formula and make simple EQ. We’ve got such a nice curve:

iir1

Next, move frequency up to 10 kHz (we’re on 44.1 sample rate) and see that:

iir2

You can see now, the perfect symmetric shape of “bell” is distorted and not symmetric now. How does it sound? Such non-symmetric curve has harsh, sharp, “digital” (in bad meaning of word) sound. But bell shape of true analog EQ doesn’t distort here. I think, symmetric curves sound more natural to our brain and thus leads to better sound perception.

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