# EQ'ing with Fixed Frequencies



## tpointon (Mar 18, 2013)

While a REW newbie, I've been making measurements and some progress using EQ. But I am stymied by the fact that REW seems to insist on choosing the frequencies for filters. I have a NAD C390DD all-digital amp (no analog inputs) that includes a rudimentary room equalization capability. It has 6 pre-defined frequencies that can be adjusted: 40 / 60 / 90 / 120 / 180 and 240 hz. For each filter, gain is adjustable in 1 db increments from -12 db to +4 db. As well, each has a setting for WIDE or NARROW. This is supposed to be a Q approximation I guess, but using RTA I wasn't able to see much difference between the two settings.

So the question is, "Is there a way to have REW limit itself to adjusting filters whose frequencies I specify in advance?" I tried using the Generic equalizer, unchecking all but the first 6 filters, and specifying Manual instead of Auto. But when I asked REW to match the target, it refuses to change 'Manual' filters. I would like to specify the frequencies and let REW find the best gain and Q values.

Thanks


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## jcmusic (Oct 26, 2012)

Just let it choose all the filters and then use just the ones you want.


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## tpointon (Mar 18, 2013)

jcmusic said:


> Just let it choose all the filters and then use just the ones you want.


It doesn't necessarily choose frequencies in my set of 6. If it says cut 4 db at 82 hz, what values would I use for my bracketing 60 and 90 hz fixed points? And, I thought (perhaps incorrectly) that it was the combined effects of all filters taken together that resulted in the closest possible approximation to the target. If so, I shouldn't be leaving any out.


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## robbo266317 (Sep 22, 2008)

Can you post your pre-equalization graph so we can see what you are trying to achieve


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## JohnM (Apr 11, 2006)

Set up 6 filters at the frequencies you have available and leave them set to Auto, then use "Optimise Gains and Qs" to have REW adjust the gain and Q settings for each filter to get the best match to the target. Frequencies will not be altered.


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## tpointon (Mar 18, 2013)

robbo266317 said:


> Can you post your pre-equalization graph so we can see what you are trying to achieve


Thanks for the offer but for now John's answer (below) did the trick. I may take you up on the offer later. Cheers!


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## tpointon (Mar 18, 2013)

JohnM said:


> Set up 6 filters at the frequencies you have available and leave them set to Auto, then use "Optimise Gains and Qs" to have REW adjust the gain and Q settings for each filter to get the best match to the target. Frequencies will not be altered.


Thanks John, that did the trick. You're an REW wizard !! (pardon the recursion)


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## GCG (Aug 22, 2013)

tpointon said:


> Thanks John, that did the trick. You're an REW wizard !! (pardon the recursion)


I believe that's *THE* REW wizard. He is the author after all.


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## GCG (Aug 22, 2013)

@John

Resurrecting and older topic. I'm upgrading my car audio and I'm looking into a 7-band quasi-PEQ with +/- 12dB gain and restricted Frequency adjustment per band. (I have to assume the Qs are fixed)










Just wondering how you would recommend I approach it.

As a suggested feature: if the "Optimize (Gains, Qs, and Freq's)" were independent check box selections it would lend itself to this scenario easier.


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## JohnM (Apr 11, 2006)

Optimising gain and frequency without altering Q probably isn't that common a use case. Could use the gain only option with fixed Q and manually tweak frequencies as required. A loopback measurement through the equaliser would show what Q setting is needed to match the filter shapes.


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## GCG (Aug 22, 2013)

Thanks for the response. 

Sounds like a plan. I had also thought of letting REW do a full optimize to localize the freq's and then a second run for just gains and see what shook out.

On the loop back I'm a little out of my depth. Is there a section of the manual you could point me to and if not, if you get time could you do a quick walk through. I don't have a usb sound card for the loop back if that's required. I'm using a UMIK and h'phone-out to the aux-in on the head unit.


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## JohnM (Apr 11, 2006)

For a loopback measurement you would need something with a line input, so either a USB soundcard or a computer that has line in as well as line (or headphone) out. To make that kind of measurement you would connect the test signal output to the input of the equaliser, then connect the equaliser output to the line input, so you are just measuring what the equaliser does to the test signal.


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