Simplified REW Setup and Use (USB Mic & HDMI Connection) Including Measurement Techniques and How To Interpret Graphs - Page 829 - AVS Forum | Home Theater Discussions And Reviews
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post #24841 of 28348 Old 05-30-2018, 04:06 PM
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Man I generated a decay sweep on my final sub calibration and the ringing is prodigious lol especially in the lower frequencies. Which troubles me since ringing in lower frequencies I’ve read is hard to treat. Is this treatable, did I do something wrong in my measurements?
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post #24842 of 28348 Old 05-30-2018, 04:19 PM
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Originally Posted by veger69 View Post
Man I generated a decay sweep on my final sub calibration and the ringing is prodigious lol especially in the lower frequencies. Which troubles me since ringing in lower frequencies I’ve read is hard to treat. Is this treatable, did I do something wrong in my measurements?
On page 81 of the Guide, it is recommended to turn off all time slices except for 160ms in order to make the graph easier to interpret. Can you do this, please?

And as for bass resonance below 40Hz, you are correct, it is very difficult to eliminate with treatments. But before you get overly concerned, think about what type of content is in the ultra-low frequencies. Not most music content, where bass resonance can destroy the mood. It is primarily LFE effects in movies, like explosions. Can you really tell the difference between an explosion that has bass resonance and one that doesn’t? Probably hard to tell. My advice: focus on managing resonances above 40Hz, which we will be able to see better if you post an updated Decay measurement, as well as a Waterfall and a Spectrogram.
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post #24843 of 28348 Old 05-30-2018, 05:01 PM
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Originally Posted by AustinJerry View Post
On page 81 of the Guide, it is recommended to turn off all time slices except for 160ms in order to make the graph easier to interpret. Can you do this, please?

And as for bass resonance below 40Hz, you are correct, it is very difficult to eliminate with treatments. But before you get overly concerned, think about what type of content is in the ultra-low frequencies. Not most music content, where bass resonance can destroy the mood. It is primarily LFE effects in movies, like explosions. Can you really tell the difference between an explosion that has bass resonance and one that doesn’t? Probably hard to tell. My advice: focus on managing resonances above 40Hz, which we will be able to see better if you post an updated Decay measurement, as well as a Waterfall and a Spectrogram.
I read your guide but can’t reproduce your graph
Could you tell me what the slice interval, window ms and rise time should be?
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post #24844 of 28348 Old 05-30-2018, 05:14 PM
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I read your guide but can’t reproduce your graph
Could you tell me what the slice interval, window ms and rise time should be?
The guide on p79 clearly shows the exact settings to use. Are you looking for something else? How about posting a download link for your MDAT file so I can look at it directly?
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post #24845 of 28348 Old 05-30-2018, 05:16 PM
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Originally Posted by veger69 View Post
Man I generated a decay sweep on my final sub calibration and the ringing is prodigious lol especially in the lower frequencies. Which troubles me since ringing in lower frequencies I’ve read is hard to treat. Is this treatable, did I do something wrong in my measurements?
Perfectly normal, and not readily treatable. As Jerry noted, it’s not that big of a deal. The main reason it looks so bad is that your level is really high.

I’d say just use a waterfall graph for this.

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post #24846 of 28348 Old 05-30-2018, 05:29 PM
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Ok I had the settings right but didn’t turn off all but 160
https://www.dropbox.com/s/8ocs85ch5k...only.mdat?dl=0
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post #24847 of 28348 Old 05-30-2018, 06:36 PM
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Quote:
Originally Posted by veger69 View Post
I read your guide but can’t reproduce your graph
Could you tell me what the slice interval, window ms and rise time should be?
All of that is in the guide....it perfectly says all this if you're looking at the REW guide in Jerry's signature which you should have downloaded when you click on his link.

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post #24848 of 28348 Old 05-30-2018, 06:36 PM
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Ok I had the settings right but didn’t turn off all but 160
https://www.dropbox.com/s/8ocs85ch5k...only.mdat?dl=0

The graph presentation is better now. You have three measurements in the file. What is "Subs all in phase filter" mean?

Clearly, the Decay graph shows an issue at 80Hz. The resonance at 40Hz as previously discussed would be difficult to fix. The frequency response measurement shows quite a peak at 40Hz, which is probably not helping the resonance at that frequency. The REW EQ tool can lower that peak:



I thought you were using REW EQ in a miniDSP device?
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post #24849 of 28348 Old 05-30-2018, 06:43 PM
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The graph presentation is better now. You have three measurements in the file. What is "Subs all in phase filter" mean?



Clearly, the Decay graph shows an issue at 80Hz. The resonance at 40Hz as previously discussed would be difficult to fix. The frequency response measurement shows quite a peak at 40Hz, which is probably not helping the resonance at that frequency. The REW EQ tool can lower that peak:







I thought you were using REW EQ in a miniDSP device?

The “subs all in phase 90db” was the raw sub sweep no filter applied
The “subs comb all in phase filter” was corrected with MiniDSP it saw that rise at 40hrz corrected for it but had no affect.
The “sub ARC cal” was the MiniDSP filter applied, then the Avm60 ARC calibration run

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post #24850 of 28348 Old 05-30-2018, 07:03 PM
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Here is my measured response and the filter it created. It predicted correcting the hump at 40hrz but the sweep with the filter applied had no affect on the bump
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post #24851 of 28348 Old 05-30-2018, 07:28 PM
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Here is my measured response and the filter it created. It predicted correcting the hump at 40hrz but the sweep with the filter applied had no affect on the bump
I see now. I was applying the EQ to the measurement after ARC, which is wrong. Too bad the PEQ isn't more effective. The measurement after the ARC Calibration is still not great.

BTW, I can get slightly better results if I set "Match Range" to be 20-70Hz. This is more reasonable, since nothing is going to touch that weird dip at 80Hz. Wonder what is causing that?
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post #24852 of 28348 Old 05-30-2018, 07:36 PM
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I see now. I was applying the EQ to the measurement after ARC, which is wrong. Too bad the PEQ isn't more effective. The measurement after the ARC Calibration is still not great.



BTW, I can get slightly better results if I set "Match Range" to be 20-70Hz. This is more reasonable, since nothing is going to touch that weird dip at 80Hz. Wonder what is causing that?


It’s confusing to me too it’s. It’s in the individual sweeps too even the rear sub


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post #24853 of 28348 Old 05-31-2018, 06:06 AM
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It’s confusing to me too it’s. It’s in the individual sweeps too even the rear sub
Can you measure different places in the room? Maybe it's a placement issue. You might not be able to do anything about it but at least you'd know the reason.
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post #24854 of 28348 Old 05-31-2018, 06:13 AM
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Here is my measured response and the filter it created. It predicted correcting the hump at 40hrz but the sweep with the filter applied had no affect on the bump
The prediction is generally very accurate. It looks likely that your filters are simply not being applied, either not loaded correctly into the 2x4 HD or in some way disabled.
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post #24855 of 28348 Old 05-31-2018, 11:58 AM
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Can you measure different places in the room? Maybe it's a placement issue. You might not be able to do anything about it but at least you'd know the reason.
yes I’ll attempt today

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The prediction is generally very accurate. It looks likely that your filters are simply not being applied, either not loaded correctly into the 2x4 HD or in some way disabled.
Well the filter obviously worked in other areas of the curve but maybe I’ll know more with a little more experimentation
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post #24856 of 28348 Old 05-31-2018, 09:57 PM
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I ran sweeps +3, +2’, +1’ MLP they all showed dips at 45-60hrz. I got better results this time at the MLP and the filters seemed to apply this time. So I guess the dip is something I’m going to have to deal with till I treat the room.
https://www.dropbox.com/s/xsqk2t3tkehz6pt/SUB.mdat?dl=0

The pics are,
1. the corrected sweep at MLP.
2. Four measurements surrounding the MLP at least 2’ feet apart, all exhibiting the dip.
3. Waterfall
4. Decay
5. Spectrogram


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@veger69 sub pos4 looks the best with the smallest dip at 50hz. Also can you show subs + center?

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post #24858 of 28348 Old 06-01-2018, 08:04 AM
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Originally Posted by veger69 View Post
I ran sweeps +3, +2’, +1’ MLP they all showed dips at 45-60hrz. I got better results this time at the MLP and the filters seemed to apply this time. So I guess the dip is something I’m going to have to deal with till I treat the room.
In my experience, treatments don’t raise dips. They tend to address resonances.
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post #24859 of 28348 Old 06-01-2018, 09:44 AM
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@veger69 sub pos4 looks the best with the smallest dip at 50hz. Also can you show subs + center?
Unfortunately erred that position 4 was on the outside edge of my right seating position. All the center position had the dip. I tried +3’mlp, +2’mlp, +1’mlp all showed dip.
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In my experience, treatments don’t raise dips. They tend to address resonances.
Jerry I guess I stuck with it then I can try them in the corners when my new sub patch cable get here. I’m limited on space as you can see





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post #24860 of 28348 Old 06-01-2018, 12:15 PM
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Jerry I guess I stuck with it then I can try them in the corners when my new sub patch cable get here. I’m limited on space as you can see
Yes, that looks pretty tight. BTW, why do you point the tip of the mic downwards? The general guidance is to point it towards the ceiling, with the tip exactly at ear-height. You might try to see if that makes a difference.
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post #24861 of 28348 Old 06-01-2018, 12:24 PM
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Yes, that looks pretty tight. BTW, why do you point the tip of the mic downwards? The general guidance is to point it towards the ceiling, with the tip exactly at ear-height. You might try to see if that makes a difference.


I switch it to downward for these measurements because with the booms height I wasn’t able to get the mic at ear level for all measurements. Weirdly the filters didn’t start acting right until I turned it down. I’ve seen pictures with the mic in that position, is it really different as long as it’s 90deg?


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post #24862 of 28348 Old 06-01-2018, 12:37 PM
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I switch it to downward for these measurements because with the booms height I wasn’t able to get the mic at ear level for all measurements. Weirdly the filters didn’t start acting right until I turned it down. I’ve seen pictures with the mic in that position, is it really different as long as it’s 90deg?


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Not sure. I always point it at the ceiling, which is why I recommended at least giving it a try to see if there are any differences.
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post #24863 of 28348 Old 06-01-2018, 01:00 PM
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Looks the same to me


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post #24864 of 28348 Old 06-01-2018, 01:14 PM
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Looks the same to me

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OK, agreed, but I still recommend pointing the tip of the mic towards the ceiling.
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post #24865 of 28348 Old 06-01-2018, 01:18 PM
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...
IIRC, I had a dip like that for a while. I think it's what prompted me to get another subwoofer.

Nice thing about that dip being in the 40-60Hz range is that you don't need a monster sub to fill it in. I think an 8" sub will do just fine.
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post #24866 of 28348 Old 06-01-2018, 03:30 PM
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IIRC, I had a dip like that for a while. I think it's what prompted me to get another subwoofer.

Nice thing about that dip being in the 40-60Hz range is that you don't need a monster sub to fill it in. I think an 8" sub will do just fine.


Unfortunately I have three. two VTF-15HMK2 and one LMF-1 EX, all decent subs and all individual sweeps showing a dip at 40-60hrz. For a 16x12 room that should be more than enough. I have one shot left I’m going to place the front subs in the corner and see if that helps


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post #24867 of 28348 Old 06-01-2018, 05:35 PM
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Unfortunately I have three. two VTF-15HMK2 and one LMF-1 EX, all decent subs and all individual sweeps showing a dip at 40-60hrz. For a 16x12 room that should be more than enough. I have one shot left I’m going to place the front subs in the corner and see if that helps


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Why I find most interesting is that all three subs, which are placed in different spots in the room, are all showing the same dip in the 40-60Hz range. I would think that to be highly unlikely.

Being an amateur detective, I would devise a test to figure out what is going on. For example, launch REW, open up the tone generator, and set it up to generate a 50Hz sine wave on HDMI4 (LFE). Place the mic near the center of the room, say 2ft to the left of the MLP. Turn off all but one sub. Output the 50Hz tone and record the output level as shown on the REW SPL meter. Without moving the mic, turn off the first sub and turn on the second sub. Output the test tone again and measure the level. Continue until all subs have been measured at position 1. Now move the mic to a second position, say 3ft behind the MLP. Re-run the level test for each sub at this new location.

After you have gone through this exercise for at least two mic positions (or more), compare the output results. There should be a significant variance among the measurements, from sub to sub, and from mic position to mic position. In my room, for one position and for four subs, I received measurements of 70, 74, 82, and 80. You should see the same variability. And as you move from one mic position to another, the output level for 50Hz should change. In other words, there is no way that you should see low levels at 50Hz for all subs at all positions, unless something is wrong with your measurement gear.

So what does this exercise prove? It shows that there has to be someplace in your listening room where the 40-60Hz dip doesn’t exist. Of course, that may be in a spot where it is impossible to locate a sub. If that is the case, then that is bad luck indeed.
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post #24868 of 28348 Old 06-01-2018, 08:14 PM
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Jerry I’ve seen the same results with the Anthem ARC mic using the Quick measure feature of ARC

And the same dip in the FL, FR, and C channels

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post #24869 of 28348 Old 06-01-2018, 08:25 PM
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Jerry I’ve seen the same results with the Anthem ARC mic using the Quick measure feature of ARC[
And the same dip in the FL, FR, and C channels


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I am puzzled. There should be areas of the listening room that don’t show that dip.
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post #24870 of 28348 Old 06-02-2018, 05:49 AM
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Try a different measurement position rather than a different source position.
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