# using REW for rt60 ?



## anwaypasible (Aug 5, 2010)

i have a shure es615 microphone (50 ohms dynamic) with an xfi elite pro soundcard going to a sony receiver which powers some oldschool car audio gear from the early 1990's era.
stillwater(kicker) tweeters
kicker 'resolution' r5 midranges
mtx blue thunder (blue cone) 12 inch woofers

i had some peerless NHT surplus drivers, but i slapped the bottom of one and 'adjusted' the voice coil, which now makes an unpleasent scratchy noise & distorts.. they are the rather famous NPT-11-081-1 model number.
for now i am playing with what i have, while i might buy some more of those NHT/peerless woofers.. or i might buy some new HDS/nomex ones from parts express or madisound.

anyways..
i am used to using trueRTA with its internal pink noise generator to calibrate my equalizer.. but i have recently come across the reverb function of my soundcard.
my living room also serves as my bedroom, and as such, there isnt much furniture/cloth in the room.
it is about 12ft x 13ft with about 7.5ft ceiling.. and i have used the online reverb calculators to get an rt60 value for the size and somewhat of the wall/floor/ceiling absorbsion characteristics.
but..
if room eq wizard can help me get a more precise value for my room, i'd like to move forward with learning.

the room is small yet there is a concrete floor with wood paneling on the walls and plaster on the ceiling.
the only fabric 'horizontally' is the moon chair along the back wall and some towels hung over the window to keep the sun from raising the internal temperature of the room (and a plastic/fluff coat hanging from the door)

i can hear subtle echos when i move my computer chair or pop a toe.. and from what i understand, using reverb can help those echos come to silence faster than doing absolutely nothing.

in simple mode my reverb software that comes with the xfi soundcards has three knobs.. and in advanced mode there are twenty-two knobs.
i think i have been able to define somewhat what half of the knobs do.. and i would like to know if anybody can touch base with me on the ones i have already come to grasp a concept with.. maybe you can reassure me that i have come to understand these few knobs correctly.

but also, i would like to know how room EQ wizard can help.
i have taken an early EQ adjustment to compensate for the room while i wait to dial in the reverb settings.
i know that once i have the reverb settings i will need to allow that software to work and re-calibrate the equalizer since there will be less peaks and/or other/new areas of concern.

i will attach a photo of the image i have taken with R.E.W. just to kick things off a bit.. although i'd like to mention that i am new to this software and dont understand much other than the noise that i heard was inputted into the computer and is now being displayed visually.

(although having had a look.. it doesnt appear that i can upload anything until my 5 posts are made)


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## laser188139 (Sep 19, 2009)

For getting to five posts, there is a post padding thread here.


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## anwaypasible (Aug 5, 2010)

i'm not embarassed to use this thread to raise my post count to five.. i'll bump the thread back to the first page if i have to while i wait.

:dumbcrazy:


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## anwaypasible (Aug 5, 2010)

i managed to make it to my fifth post and here is the image of my response:


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## laser188139 (Sep 19, 2009)

I don't know anything about the reverb software you will be using, so I doubt I can help you there. 

If you are interested in the range above 100Hz, the RT60 window gives you a choice of decay measure (Topt, T20, T30, EDT) and a choice of looking at the data averaged over one octave bands or 1/3 octave bands. 

For the sub range, in the newest beta v5 release John has added a new feature to the EQ panel under Modal Analysis, where you can ask it to calculate resonances up to a limit frequency. This gives a list of resonant frequencies, the peak dB, and the corresponding T60 decay. 

Obviously you get a visual impression of where the resonances occur from the waterfall window. The nice thing about the quantitative T60 values in the new Modal Analysis is it separates the delay information from the initial peak levels. It's sometimes hard in the waterfall to distinguish between excessive delay from resonances and apparently excessive delays from initially high starting levels. 

Have fun,
Bill


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## anwaypasible (Aug 5, 2010)

thanks for that little bit of information.. i havent used the waterfall yet but i think the problem you helped me avoid is rather nice.

my sixth post didnt let me post a picture.. maybe my seventh will:


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## laser188139 (Sep 19, 2009)

This time, your picture is visible. For some reason, the earlier one I could see when I was editing a response, but it was not visible when I returned to the normal thread view. Weird. 

When posting graphs, the recommendation is to set the vertical range to 45dB - 105dB, unless there are special reasons for something different. 

For full range responses, you will want to use some smoothing to see visually what is happening. With REW v5, you can select this in the SPL view by clicking on Controls. In the Overlay window, the Controls will let you apply the same smoothing to several curves at the same time. You can also set the default smoothing for new measurements in the Preferences -> Analysis tab. The general recommendation seems to be to choose 1/3 octave smoothing; I usually use 1/6. Any less smoothing and you begin to worry too much about small stuff. 

It makes sense to leave the smoothing off when looking at the sub range alone. 

Bill


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## anwaypasible (Aug 5, 2010)

this is your second implication towards using the version 5 beta.. is the program really stable enough to be suggesting that people use it?

no bugs that affect the results i would hope .. because if that is so, i will install the new version 5 and give things another go.


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## laser188139 (Sep 19, 2009)

It has been pretty stable since the first beta version. Before the last version, John indicated he was near the point to call the release done.

I was only describing where to find the controls for smoothing relative to version 5 under the assumption that you would be using it. One can control smoothing under v4.11, it's just found a little differently, and one doesn't have the ability to change the smoothing of several curves all at once to the same value. 

Bill


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## anwaypasible (Aug 5, 2010)

i switched to v5 and took a new measurement:










the rt60 window looks weird to me because there is a huge line at 1.212s as shown below:










my reverb knobs look like this:










the first picture shows a dip at 125hz and trueRTA says there is no dip.. so i tried to use the RTA software within R.E.W. and i dont think it works.. the averages are stuck and the line doesnt move despite cranking the note on the equalizer all the way up.. far too insensitive, perhaps not finished.
i've tried other RTA software and they all seem to resemble trueRTA's results.

i left 62hz high to bring up 31hz as said by trueRTA.. but this graph doesnt seem to show that 60hz is excessively high.

kinda hard to get hypnotized by audio in accurate style when there are conflicting results.. who are we supposed to turn to?


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## JohnM (Apr 11, 2006)

anwaypasible said:


> so i tried to use the RTA software within R.E.W. and i dont think it works.. the averages are stuck and the line doesnt move despite cranking the note on the equalizer all the way up.. far too insensitive, perhaps not finished.


The RTA works just fine. What were you using as the test signal for the RTA to listen to? What did you have the averaging mode set to?

RT60 figures are not very meaningful in domestic-sized spaces, you are better looking at a waterfall plot at low frequencies.

That reverb effect is for adding reverberation to recordings and has no relevance for room responses.


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## anwaypasible (Aug 5, 2010)

the signal used was from the R.E.W.'s own signal generator set on pink pn.
the length was set to 131072
averages were set to none and things were slow.. i selected each average in the list and each one was slower than the 'none' selection.
makes me think that each number should have a x100 added like an RPM gauge.

raising any of the sliders to an obnoxious level wasnt registered on the RTA except for a tiny bit with a wide Q.

apologies for the rough change/challenge from trueRTA to R.E.W.

as for the reverb.. there are settings for room size, and those are input to the size of the room that i am in with a feet to meters translation.
the reverb settings are very real and have helped remove some of the echo from the room without adding carpet or hanging blankets on the wall (or switching from wood furniture to cloth furniture in some instances).
aside from that.. i have managed to view/create some wild soundstages that span from a very wide stereo all the way to listening to the music behind me with a 2.0 speaker setup in front of me.. both of these are with the room size set to the room i am in.

i wasnt looking to create an artificial room size for an FX.. and thus i chose my actual room size and went from there.
my biggest complaint right now is the 5.25 inch woofers that i am using, i would like some more cone area from the likes of a 6.5 inch midrange to move the extra air.

my room layout is really tough too. and i am stubborn, since the speakers are not pointed in towards my ears at all and i am using the CREATIVE reverb to balance out the reflections, once for the entire room and again for the first reflection that seperates from the direct soundwave.

a little bit of echo cancels out some of the 'hum' in the room and keeps the sound from multiplying and becoming muddy.

let me know what is what with the RTA feature.


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## JohnM (Apr 11, 2006)

For a faster update use a shorter FFT setting, a 128k FFT is nearly 3 seconds of audio input at 48kHz. If the EQ settings were not affecting what was shown on the RTA then they were not affecting the output.

I don't see how adding reverb can reduce anything, but the added reverb might mask the room's own response. If you want to see what effect it is having on the output do a loopback measurement and see what the response of the reverb looks like.


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## belle69 (Apr 11, 2011)

Correct if i am wrong but RT 60 calc should use short/instant duration signal e.g Balloon burst or Gun-shot to excite reflections of hard surfaces within an enclosed space.

Only then decay of the 6 standard frequencies can be measured to find the duration of the signals.

Playing continuous music is not RT 60 testing.


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## JohnM (Apr 11, 2006)

belle69 said:


> Correct if i am wrong but RT 60 calc should use short/instant duration signal e.g Balloon burst or Gun-shot to excite reflections of hard surfaces within an enclosed space.


You are wrong. Using an approximation to an impulse is one way to get an impulse response, but not a very good one. Log swept sine is a better (higher S/N, lower distortion) way to derive an impulse response, which can then be analysed to determine the RT60 figures.


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## belle69 (Apr 11, 2011)

John, thanks for your reply -I feel quite honored to get one so quickly from the author of this marvelous program.

I am actually trying to get an RT60 plot of a staff canteen and trying to convince my management to invest in some cloud baffles as it's very fatiguing to even sit in the venue for 5 minutes -yet have a meal!.

One little question: I can't run REW 5 without the FR Sweep from the tone generator?.
I am trying to just get it to record one impulse event i.e Gun Shot or Balloon burst for the 6 RT60 frequencies.

Sorry if my question is redundant.But i have done the 'dry calc on Excel spread sheet and now need some more data to show them where the problem lies..


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## JohnM (Apr 11, 2006)

REW, like most acoustic measurement software, does not determine the impulse response by generating impulses. That would give poor quality measurements. Instead, the response to a logarithmically swept sine wave is captured and the corresponding impulse response is calculated. That method gives much more accurate results. The RT60 data is then calculated from that derived impulse response.


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