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Old 05-01-2013   #101
 
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Default Re: The RTA Walkthrough and Usage thread. With Video.

Quote:
Originally Posted by therapture View Post
Well, here ya go. First is obviously the averaged plots, taken from the headrest at center, right, and left.



And the plots overlaid with the average.



Looks like I have ALOT of EQ work ahead. What I DON'T know, is how the curve should look?! And I love the way my Car sounds at this point, I think I have done a good job of level balancing from left to right, but the peaks and valleys, what to make of them? I tried a couple EQ cuts and boosts, and while my ears hear them, they really did not seem to show up as much different after I did a second RTA run through. For instance, at 4500k, I cut 3db off on both sides, and it showed almost zero difference in the plots from session 1 to session 2. I also boosted 7k 3db and still showed practically no difference, what did I do wrong?
Here is another really good thread to go along with this one.

Quick tip using 'Auto EQ' with RoomEQ(REW)

Using housecurves makes it really easy to balance right and left. I like to do left side plus sub, then right side plus sub. Using the sub as a reference point for both sides. Try out some of the housecurves posted and make some of your own.

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Old 05-02-2013   #102
 
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Default Re: The RTA Walkthrough and Usage thread. With Video.

Quote:
Originally Posted by therapture View Post
Well, here ya go. First is obviously the averaged plots, taken from the headrest at center, right, and left.



And the plots overlaid with the average.



Looks like I have ALOT of EQ work ahead. What I DON'T know, is how the curve should look?! And I love the way my Car sounds at this point, I think I have done a good job of level balancing from left to right, but the peaks and valleys, what to make of them? I tried a couple EQ cuts and boosts, and while my ears hear them, they really did not seem to show up as much different after I did a second RTA run through. For instance, at 4500k, I cut 3db off on both sides, and it showed almost zero difference in the plots from session 1 to session 2. I also boosted 7k 3db and still showed practically no difference, what did I do wrong?
Most probably your DSP has a 1/3 octave EQ so the best tip the way I see it would be to set the REW - RTA resolution (under the settings) to 1/3 octave so you will see the curve on the very same resolution your EQ works.

You will find it much easier to tune that way.

Usually most people like the whole bass area to be up to 6db stronger than the rest of the spectrum and the rest as flat as possible until somewhere around the 12KHz and then start a graduate rolloff to about -3db up to -9db until you reach the 20hz area depending on your liking (taste in sound)

Note that in most musical recording after 16KHz or so there is hardly any "information" so trying to level the 16KHz to 20KHZ based on music would be a BAD IDEA.

I use pink noise to tune the curve and brown noise to tune the bass area.

I do it once per left side and once per right side and then I compare the avg of all of it.

Before I even do EQ, I compare that both sides - each element to each element are playing at the same level, then first TC settings and only then I do the EQ.

after that is done, listen to your refernce music and fix the pix or areas you did not like how they sound and you are good to go.

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Old 05-02-2013   #103
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Default Re: The RTA Walkthrough and Usage thread. With Video.

Quote:
Originally Posted by eddieg View Post
Most probably your DSP has a 1/3 octave EQ so the best tip the way I see it would be to set the REW - RTA resolution (under the settings) to 1/3 octave so you will see the curve on the very same resolution your EQ works.

You will find it much easier to tune that way.

Usually most people like the whole bass area to be up to 6db stronger than the rest of the spectrum and the rest as flat as possible until somewhere around the 12KHz and then start a graduate rolloff to about -3db up to -9db until you reach the 20hz area depending on your liking (taste in sound)
Well, on my 363 I can also manually enter whatever frequency I want and then adjust that, or does that not work in practice? And that crazy spike at 4500k...and the dip at 45hz...

It just seems that plot is very jagged, or is it because I chose the 1/12 resolution and am seeing small things that really are not as big as they look?


edit: So on the chart/plot...is that 5db gap using the marked lines, REALLY a 5db gap in the actual sound? (don't laugh, I am new to this, utterly) :-) ...meaning if I have a 3db dip at say, 500hz, I boost my EQ 3db there, I should see a 3db rise in the response on the plot?

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Last edited by therapture; 05-02-2013 at 06:58 AM..
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Old 05-02-2013   #104
 
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Default Re: The RTA Walkthrough and Usage thread. With Video.

Quote:
Originally Posted by therapture View Post
Well, on my 363 I can also manually enter whatever frequency I want and then adjust that, or does that not work in practice? And that crazy spike at 4500k...and the dip at 45hz...

It just seems that plot is very jagged, or is it because I chose the 1/12 resolution and am seeing small things that really are not as big as they look?


edit: So on the chart/plot...is that 5db gap using the marked lines, REALLY a 5db gap in the actual sound? (don't laugh, I am new to this, utterly) :-) ...meaning if I have a 3db dip at say, 500hz, I boost my EQ 3db there, I should see a 3db rise in the response on the plot?
Even if you can peak a specific carrier frequency - you should set the REW to work at a resolution as close as possible to your EQ resolution, you will then see that you have a better tuning ability as you are comairing apples to apples instead of apples to grapes - I hope it makes the picture in a better light.

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Old 05-02-2013   #105
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Default Re: The RTA Walkthrough and Usage thread. With Video.

Awesome thread, subbed.
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Old 05-02-2013   #106
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Default Re: The RTA Walkthrough and Usage thread. With Video.

I'll be drinking a couple beers while I play with the mic again tonight that sounds bad.

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Old 05-03-2013   #107
 
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Default Re: The RTA Walkthrough and Usage thread. With Video.

I'd love to see what you have going on, and help give some ideas on things to try. Could you test and post the following, in 1/3 octave smothing and 5 db (or ms) graph resolution:

Right mid sweep, then excess group delay at 1/6 smoothing
Right tweet sweep
Combined right sweep

Left mid sweep, then excess group delay at 1/6 smoothing
Left tweet sweep
Combined left sweep

Combined L&R sweep

Sub sweep

You should be able to show most of those clearly together on one plot, and maybe make a separate one for the combined L&R with the sub (that's how we're going to see what your crossover frequency really is). This'll give us alot to talk about.

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Old 05-07-2013   #108
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Default Re: The RTA Walkthrough and Usage thread. With Video.

Just saw this post mojo....I will run those sweeps tomorrow and get to them. I made some changes tonight that I think I like better.

I need to get into one thread or the other, this one or this one How to EQ the REW measured response curve.

Which would be better thread to continue in? I was thinking the technical forum one, since it stays up top as we add to it.

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Old 05-09-2013   #109
 
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Question Re: The RTA Walkthrough and Usage thread. With Video.

Quote:
Originally Posted by Sonus View Post
Hmm... had some time to lay with REW today after my Dayton UMM6 USB mic arrived.

However I can't seem to get rid of spikes at 1000Hz from 2kHz and up?:
Were you able to correct this, Sonus? I am having the same spikes. Seems strange to be a soundcard calibration issue, considering I don't have the soundcard selected as an input or output device in the preferences menu...
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Old 06-02-2013   #110
 
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Default

Quote:
Originally Posted by Sonus View Post
Hmm... had some time to lay with REW today after my Dayton UMM6 USB mic arrived.

However I can't seem to get rid of spikes at 1000Hz from 2kHz and up?

The noise measured is only background noise, but it is the same with different background noise

I've downloaded the cal file from daytonaudio.com and loaded it into REW.

EDIT: measured my Bose Quietcomfort15 headset with pink noise
Quote:
Originally Posted by Fetus View Post
Were you able to correct this, Sonus? I am having the same spikes. Seems strange to be a soundcard calibration issue, considering I don't have the soundcard selected as an input or output device in the preferences menu...
This is an issue with the UMM-6, the UMIK-1, and probably most of the other USB microphones available. I have the UMM-6 and it confused the hell out of me when I first started using it to take measurements. I initially thought that the giant spikes at 1khz were due to the impedance peaks of my tweeters, but when none of my EQ/crossover adjustments made any difference, I checked the response without any input signal and the spikes were still there.

Measurements I took in a silent part of my house:



The EMM-6 is running through my Art Dual Pre, which seems to have the same USB-related noise spikes.

Here's a link to a discussion about this issue on the AVS forums:

http://www.avsforum.com/t/1449924/si...et-graphs/1170

Possible explanation:

"The 1Khz distortion and its harmonics are clearly present as stated. Likely the cause is the USB frame sync which has a time of 1 msec or frequency of 1000 Hz. The device simply does not have proper isolation between its digital and analog sections (common problem when components are packed together this close and not enough attention is paid to such an issue."

The spikes shouldn't affect your measurements as long as you take your measurements at a level that is sufficiently above the noise floor (~ 70dB or higher). Also, since the spikes are so narrow, you can pretty much negate their effect by applying some smoothing:

No smoothing:



1/12 Octave Smoothing:



1/3 Octave Smoothing:


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Old 05-23-2014   #111
 
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Default Re: The RTA Walkthrough and Usage thread. With Video.

Do not rely on generic calibration files, which could be easily founded at a lot of sites. My ECM8000 has a raise of up till 9 dB at higher frequences and no generic calibrations were able to match my mic. Do calibration by yourself or let professionals to do it. Be careful with corrections at low frequences. Very often they say more about room acoustics than the microfon itself.
My point - individual calibration of mic is must for correct measurements.
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Old 06-07-2014   #112
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Default Re: The RTA Walkthrough and Usage thread. With Video.

so, yea, what happened to the rest of this?

will there ever be impulse measurements? time delay? waterfall?

is there a different tutorial somewhere on how to set up and use REW? The RTA part was super helpful but not what im looking for.

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Old 01-08-2015   #113
 
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Default Re: The RTA Walkthrough and Usage thread. With Video.

I know that this is an old thread, so don't be at me up too bad. But when you were referring to moving the mix around to different spots at different heights, would I need to adjust the angle as well? So 45 to the right and left maybe even 90. The reason I am asking is because I am using LARSA through audio Tools and it gives me the a ability to file save and average up to eight impulse responses.
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Old 06-04-2015   #114
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Default Re: The RTA Walkthrough and Usage thread. With Video.

Damned, still so many good readings on this site, we need a "thanks" button!
Or does it exist?

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Old 09-26-2015   #115
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Default Re: The RTA Walkthrough and Usage thread. With Video.

Thanks to the OP, great to have an easy to follow step by step guide like this - some guides seem to really start at the deep end and only go deeper.

I'll apologise in advance if my question doesn't belong here, but I've searched Google and here with no luck.

I've got a cheap RE audio 12" in a ported box about 1.5cuft tuned about 38hz (from memory, what ever the manufacturer specs recommended for SQ) in the trunk of a small sedan facing the rear up against the back seat. If I use REW with a UMIK-1 in the listening position for a "measurement" (sine sweep right?) from say 10-200hz no eq no xover it shows a ~25dB dip around 40 hz, only about 3-4hz wide but otherwise pretty flat between 30-80hz. With the trunk open the response is very flat, but about 25dB lower, ie all other frequencies drop to the level of the dip with the trunk closed. Face the sub up, sideways or forwards no difference. Back seats down still the same. During the sweep you can really hear the dip as if it's muted at 40hz.

But fire up the RTA with pink noise (using REWs generator on sub cal and the RTA set to take 16 sample average with either 1/3 or 1/6 smoothing) as per the OPs YouTube video and its only about 10dB down though a bit wider. Auto EQ with REW to my minidsp and it's looking perfect, sounds pretty good but the measurement sine sweep still sees a dirty big 15dB dip, though it's a lot harder to hear now.

Which one should I go by?


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Old 09-26-2015   #116
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Default Re: The RTA Walkthrough and Usage thread. With Video.

One more question, is it considered poor form to use pink noise and an RTA to fine tune time alignment?

Everything I've read says it's not that simple. First I got it close to what sounded right, but on the RTA I could see a slight dip either slightly before or slightly after the xover point between sub and 8" mids. Adjust delay in real time by 0.1ms increments until it's basically right on the xover point which also really smooths out the frequencies above and below, sounds great too. I haven't worked on the dip much yet, but it seems to match the curve of the drivers when measured one at a time.

It's not supposed to be that easy is it?
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Old 10-15-2015   #117
 
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Default Re: The RTA Walkthrough and Usage thread. With Video.

So, I'm trying to take some simple RTA measurements using a Dayton Umm6, their provided calibration file, and uncorrelated (stereo) pink noise.

My measurements are coming up with more slant than my ears hear. Comparing it to the Andy housecurve you'd think it was super bass heavy (+30db above vocals) and dull up high (-15db from 4k up).
RTA with house curve.jpg

So, I found a quiet place in my house and turned on the RTA to see what the mic picked up....and it seems "slanted"...sorry forgot to smooth it, but you can see 20Hz is about +30db!
RTA without Pink noise playing.jpg

Did I miss a step in my setup? Or a preference? Or?

Thanks in advance for any insights!

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Old 10-17-2015   #118
 
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Default Re: The RTA Walkthrough and Usage thread. With Video.

For anyone else running into this, I got my answer over on HomeTheaterShack (home base for REW)

Quote:
You have the RTA in spectrum mode, select an RTA mode for an RTA-style display. Use these settings:
RTA settings.jpg
Now onto tuning
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Old 10-17-2015   #119
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Default Re: The RTA Walkthrough and Usage thread. With Video.

Huge difference
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Old 10-17-2015   #120
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Default Re: The RTA Walkthrough and Usage thread. With Video.

I also noticed you have the "Adjust RTA Levels" checked. Any reason as to why?
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Old 10-17-2015   #121
 
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Default Re: The RTA Walkthrough and Usage thread. With Video.

Just because it was that way in the settings image JohnM from HTS recommended. I haven't read up on what it does...


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Old 10-17-2015   #122
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Default Re: The RTA Walkthrough and Usage thread. With Video.

I've always used Spectrum at 1/6 up to 1/24 smoothing. You got me wondering now to try the RTA Mode. Post link to your discussion...love to read it.
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Old 10-17-2015   #123
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Default Re: The RTA Walkthrough and Usage thread. With Video.

RTA mode....what a difference. Glad you posted that. Spent the last couple hours playing around.
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Old 10-18-2015   #124
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Default Re: The RTA Walkthrough and Usage thread. With Video.

The difference between spectrum and RTA modes is how the information is presented.

In spectrum mode the frequency content of the signal is split up into bins that are all the same width in Hz. For example, with a 64k FFT length and 48 kHz sample rate the bins are 0.732 Hz wide. The plot shows the energy in each of those bins.

In RTA mode the bin widths are an octave fraction, so their width in Hz varies with the frequency. For example, a 1 octave RTA plot has bins that are 70.7 Hz wide at 100 Hz and 707 Hz wide at 1 kHz. The plot shows the combined energy at each frequency within each bin. This is closer to how our ears perceive sound.

The different presentations mean signals with a spread of frequency content will look different on the plot. The best known examples are white noise and pink noise.

White noise has the same energy at each frequency. On a spectrum plot, which shows the energy at each frequency, the white noise plots as a horizontal line. On an RTA plot it appears as a line that rises with increasing frequency, as each RTA bin gets wider it covers more frequencies and so has more energy, the bin widths double with each doubling of frequency so the energy also doubles, which adds 3 dB on the logarithmic plots we use to show level. White noise sounds quite 'hissy', we perceive it as having more energy at higher frequencies.

Pink noise has energy that falls 3 dB with each doubling of frequency. On a spectrum plot it is a line that falls at that 3 dB per octave rate, on an RTA plot it is a horizontal line as the energy in the signal is falling at the same rate as the bins are widening. We perceive pink noise as having a uniform distribution of energy.

Single tones are a special case, they will appear at the same level on either style of plot as their energy is all at one frequency, so on a spectrum plot they show as a vertical line, on an RTA plot they show (typically) as a bar of the width of the bin width at their frequency, but the height of the bar is the same as the height of the line on the spectrum as all the energy is at that one frequency.

Read more: Need some help figuring out what happened - Home Theater Forum and Systems - HomeTheaterShack.com
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Old 11-02-2015   #125
 
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Default Re: The RTA Walkthrough and Usage thread. With Video.

Further interpreting JohnM's feedback over on HTS,

Note his comments about random (uncorrelated) pink noise...
Quote:
over any short period its spectrum can deviate significantly from the ideal especially at low frequencies
Quote:
Random pink noise typically has a crest factor of around 12 dB
That means to get a reasonably accurate (to within a few dB) view of the response at a single position you would need to leave the mic stationary there for about 30s, with the RTA averaging all the while.
Quote:
[B]Random pink noise is pretty useless for measuring responses./B]
1.5sec of Random (uncorrelated) Pink Noise


Compare the 20-200Hz range when averaged for 30sec!



When I have been taking RTA measurements (at 6 mic positions and then averaging) I'm fairly sure I'm capturing "milliseconds" and getting random snapshots (Avergaing was set to "none") that (in the lower frequencies) vary up to 12db from the PN alone!

I haven't used periodic PN yet, but I did try the RTA Average settings on 32 averages and it definitely improved the the "resolution", which will keep me from tweaking the EQ 1db here 2 db there when it was only a snapshot of PN variation...and not representative of what I hear.
RTA settings.jpg

Now I've got to figure out which of these dips/combs I can actually do anything about with EQ Insights welcomed!
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