Parametric (Peaking) EQ variations

6908 Views 13 Replies 4 Participants Last post by Chester, Nov 26, 2009

Chester

Discussion Starter · Oct 26, 2009

Hi; I have been using various programs to design EQ filters over the years including REW WinISD Pro, Crown Audio's IQ for Windows, Aixcoustic's Electri-Q, the UFX plugin (on KX drivers) etc. One thing I have noticed over time is how the Q of Parametric EQ filters varies from program to program; ideally the graph of one parametric EQ in a program (given the same ranges on the frequency and db axes) would look the exact same in another program. This rarely is the case. WinISD Pro (which every released version I know of there is a bug with 'negatively' gained parametric EQ's (ex. 2 parametrics both centered at 1000 hz, both a q of 2, one negative with a negative gain and one with positive (but same) gain will not cancel out). I have found formulas to correct this (and in the 'next release' of Win ISD it should be fixed) however this just goes to show how important it is to double check graphs.

I am currently working on a conversion from REW to Crown Audio's IQ for Windows; if anyone else has any information on this sort of thing it would be greatly appreciated. I am guessing that there hasn't been any discussion about how the Q is calculated on various programs though...

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Wayne A. Pflughaupt

· #3 · Oct 26, 2009

Chester said:
So clearly both programs are using different methods of calculating the shape of the filter even though they both are using "Frequency" "Gain" and "Q".

Yes. I’m sure brucek will be along eventually with the mathematical formulas, but basically there is no universal standard for filter Q. It’s different from one equalizer to the next, and one would have to assume, one equalizing program to the next.

To give you an example, here are graphs from three popular parametric EQs. All show the electrical response of filters set for 1/3-octave, which typically translates to ~4.3-4.5Q

Behringer DSP1124

Velodyne SMS-1

Behringer FBQ2496

Regards,
Wayne

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Wayne A. Pflughaupt

· #5 · Oct 26, 2009

Chester said:
... or if there is a way to add the USM-810 to the list that would be great too (I just noticed that the 'supported devices' have quite a few limitations on various parameters (TMREQ only allows +6 db gain, SMS-1 only goes to 120 hz, etc.)

That's because REW is programmed for the built-in limitations and parameters of those equalizers. What good would it do for REW to show a +10 gain for the TMREQ if it won't do that?

Regards,
Wayne

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Wayne A. Pflughaupt

· #7 · Oct 26, 2009

Understood. :T This site has the formulas - maybe it will be helpful.

Regards,
Wayne

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