# Video: REW RTA and Plugin used for Room Correction.



## DozerMayne (Dec 15, 2008)

Here is a youtube video I just did showing me using REW to create filters, that I input into a vst plugin in my DAW on the master out, to use as an alternate mixing reference.
I demonstrate how to generate the filters, and show Real Time Analysis of the before and after.


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## mechman (Feb 8, 2007)

Thanks for the video Dozer. :T


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## JohnM (Apr 11, 2006)

Great job 

A couple of things on the RTA: when you use a noise signal as a stimulus it is best to set the window to Rectangular. You can then also take advantage of a nice property of the Pink PN signal, which is that it gives very good results with _no_ averaging (because, unlike random pink noise, each complete sequence contains all frequencies at the correct levels and matches the FFT length, with random pink noise the levels are only correct over a (very) long average, especially at the low end). 

As a final tip, if you tick the "Adjust RTA levels" box the RTA graph will be drawn at levels that are comparable to your measurements.


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## DozerMayne (Dec 15, 2008)

Right,...LOL..glad you caught that.
I was previously generating random pink noise before the tutorial, and never switched it.
Thanks for the heads up..
I will add that as a note in the videos "More Info" section, and as an annotation..within the video.

page 98 of the PDF manual.
*Window*
_The FFT resolution is also affected by the Window setting. Rectangular windows give the best frequency
resolution but are only suitable when the signal being analysed is periodic within the FFT length or if a
noise signal is being measured. The Rectangular window should always be used with the REW periodic
noise signals_

Page 67-68
*Pink and White Periodic Noise*
_Periodic Noise (PN) sequences are ideally suited for use with spectrum and real time analysers (RTA's).
They contain every frequency the analyser can resolve in a sequence length that matches the length of the
analyser's FFT. Their great benefit is that they produce the desired spectrum shape without requiring any
averaging or windowing, so the analyser display reacts much more rapidly to changes in the system than it
would if testing with Pink or White random noise, making them ideal for live adjustment of EQ filters. Use
Pink PN when measuring with an RTA or White PN with a Spectrum analyser._

_The Length control must be set the same as the length of the FFT used by the analyser. If it is set shorter
than the analyser FFT there will be notches in the analyser display, as the periodic noise will not contain
some of the frequencies the analyser is looking for. If it is set longer the extra frequencies will give a noisy
display requiring more averaging. The images below show the effect of correct and incorrect settings of
the PN length for a loopback measurement with 1/48 octave RTA that is using an FFT length of 65536
(64k).

The Save PN to WAV file button generates a 16-bit stereo wave file containing the PN sequence in both
channels. The file duration is approximately 1 minute, the level is per the RMS Level setting of the signal
generator. This file can be used to generate a test disc to be played on a system whose response is to be
measured. Make sure that the current soundcard sample rate corresponds with the format of the disc to be
made - for example, 44.1kHz should be used if generating a CD, or 48kHz for a DVD. When measuring
the system the sample rate and FFT length must be the same as used for the test disc._

And as for the "Adjust RTA levels" tick, I thought it would be better to be offset, for better viewing.
Thought some would get confused with all the squiggly lines meshing together...


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## jlird808 (Nov 2, 2010)

Thanks for posting the vid...I been fooling around with REW all day now cuz of it lol...

I also use Cubase and have an EMU PCI card (0404). I noticed when I play the Pink PN in Cubase and put the eq on the master stereo out I can no longer get REW to work (and vice versa). I'm sure its cuz both programs want to use the ASIO driver and neither is willing to share lol. 

Any way around this? 

Also, Ive been using/adjusting the eq on Emu Patchmix's ASIO Out channel instead. Im sure it's the same as putting it on the Cubase master out, however, Patchmix only lets u adjust eq as low as 80hz!! :unbelievable: Hence I had to do the rest in Cubase (goes down to 20hz)....except now I cant tell how my 20-80hz adjustments sound in REW since they wont work at the same time :hissyfit:

Any thoughts? Can I switch REW to WDM or some other audio driver instead of ASIO? 

***EDIT*** I switched REW over to Java and sent the PCI In (mic) to Wave and now I can monitor/measure Cubase!! Thx...


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## DozerMayne (Dec 15, 2008)

Not sure of a way around it. Just get a laptop, and an external quality sound card. And use that for measurement. Best solution.


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## DozerMayne (Dec 15, 2008)

Just an idea..
Many audio production mixing and mastering people use your software to measure their studios.

I got the idea one day, to use the suggested correction filters, and input them into a EQ plugin, 
on the master buss of your recording software, as an alternate reference. 
I have a video that show how to do all of this.
Its in the first post of this thread.


You basically load the PinkNoise PN .wav into your DAW, put EQ plugin with corrected filters 
as insert on master buss, and play it while doing RTA in REW. 
This plays the PinkNoise PN .wav with the correction, and it smooths
out the frequency response.

OK, so what about the "time domain"? How does this effect that?

Here is the idea.

I am sure, somewhere in the program, embedded in the .exe, there is the 
"sine wave sweep" .wav file, used for the measurment sweep.

If you were to update REW, so that the sweep .wav file could be exported, and re-imported, 
this is what could be done with.
There would also be a button that automatically reloads the original sweep .wav file, 
to return to default.

After exporting the sweep as a .wav file,
I could load the sweep .wav into my DAW or audio recording program, and then do an 
offline process, to effect the sweep .wav, with an EQ, set with the correction filters. 
I would then reload the effected sweep .wav file into REW, and use that sweep file 
during the measurement. 
So, this plays the effected sine wave sweep, during the measurement.

Then I would be able to see, of course, the corrected frequency response, but 
also the other time domain stuff..waterfall, RT60, ect..


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## AVoldMan (May 15, 2011)

DozerMayne said:


> ... I demonstrate how to generate the filters, and show Real Time Analysis of the before and after.


Thanks for an excellent tutorial! I have seen some of your other REW videos on the internet, they are always filled with some personality :rofl:. This one is your best, especially considering the involved process. It's very thorough and has all the bases covered with details explained.

I have been trying to get around to this project for both my computer speaker system and HT setup. I will definitely reference this video again. Maybe a permanent "sticky" link?

I really liked the real time "with and without EQ filter" comparison at the end. It really does show the great results! BTW subjectively how does the mixing sound with and without EQing? Big change?


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## AVoldMan (May 15, 2011)

JohnM said:


> Great job


John,

:clap: for REW software!!!! I am in awe of your program! I once used to work in the NVH (noise/vibration/harshness) at Ford 30 years ago. We did similar frequency spectrum measurments that REW is capable of with a PC and decent mic. However, we had a $30,000 HP minicomputer about $5,000 of B&K microphones and preamplifiers in a 6 foot tall, 200 pound rack. It just amazes me the progress in performance and cost reduction that PC technology and internet has allowed! Truly, amazing!!!! Thanks again for your awesome work!!! :clap:


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## DozerMayne (Dec 15, 2008)

Only recommendation is, regarding the highend frequencies, 
If using an ECM8000 pointed at the ceiling, the highend will not be represented well.
So the filters generated for the high frequencies, will be pretty extreme/high in dB.
So, on the Eq you use in your DAW, you would lower the gain on those to taste.


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