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Room EQ Wizard Question (testing preamp frequency response)
Old 10th September 2009
  #1
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Room EQ Wizard Question (testing preamp frequency response)

i've been passing white noise bursts through my outboard preamps, and then importing them as impulse responses into Room EQ Wizard. i then inspect them in the "spectrum" view, hoping to learn about the frequency response of my preamps.

i know that's not how Room EQ Wizard was intended to be used, but is it accurate in manner? does importing white noise bursts as impulse responses into REW make for accurate inspection? is there a better way to do this?
Old 10th September 2009
  #2
Gear Guru
 
Ethan Winer's Avatar
 

I've never used REW for that, but it should work. It seems to me the better way is to send your sound card output to the preamp input, probably through a 20 dB pad. Then send the preamp output back into your sound card. When you run REW it will sweep a sine wave and record the result you can display as a "room" response.

It's trivial to make a flat preamp. So unless your is intended to add "color," it's probably very flat from 20 Hz to 20 KHz.

--Ethan
Old 10th September 2009
  #3
I haven't used REW, but you need to be aware that no electronic compensation can correct for aberrations in room response due to room modes. The laws of physics preclude it.

If your room is overly damped with too much acoustic treatment and doesn't exhibit any modes - which is highly unlikely - perhaps electronic EQ could compensate a bit, but it's the wrong way to go about it. The correct way is to adjust the acoustical treatment. Electronically adjusting the EQ will introduce phase shift and also may lead to overdriving your tweeters and possibly damaging your hearing if you're trying to compensate for a lack of highs caused by too much absorption.

Using something like REW as a strictly analysis tool is useful if you know what you're doing.

I'm surprised Ethan didn't mention this........
Old 10th September 2009
  #4
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Quote:
Originally Posted by Ethan Winer View Post
I've never used REW for that, but it should work. It seems to me the better way is to send your sound card output to the preamp input, probably through a 20 dB pad. Then send the preamp output back into your sound card. When you run REW it will sweep a sine wave and record the result you can display as a "room" response.

It's trivial to make a flat preamp. So unless your is intended to add "color," it's probably very flat from 20 Hz to 20 KHz.

--Ethan
good though, thanks.

that is that is exactly what i just tried, expect with FuzzMeasure...which i just discovered. i found it to be more user friendly than REW.

oh, and i'm testing preamps that i built...so i'm hoping to see flat 20-20k. that would be great!
Old 10th September 2009
  #5
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oh, one other thing i'm wondering. ethan, you mentioned padding the output before sending it into the preamp...

i'm sending the test file out of the balanced analog outputs of a motu 828mkII...would it be more accurate to hit a direct box or just an attenuator before i go into the preamp? or is that the same thing?

i have a pretty nice active DI, and i also have some simple inline XLR attenuators...what would be the proper way to go from the balanced TRS output of the MOTU into the XLR of the preamp?
Old 11th September 2009
  #6
Gear Guru
 
Ethan Winer's Avatar
 

Quote:
Originally Posted by ghetto3jon View Post
would it be more accurate to hit a direct box or just an attenuator before i go into the preamp? or is that the same thing?
You need a pad because it's a line level signal. Now, maybe the preamp can take a "lowish" line level signal. But still, you'll want to test the preamp at various gain settings, so you need a way to pad the input. Even a $2.00 10k potentiometer can do this.

--Ethan
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