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Simplified REW Setup and Use (USB Mic & HDMI Connection) Including Measurement Techniques and How... - Page 96

post #2851 of 9620
Quote:
Originally Posted by AustinJerry View Post

Something doesn't look right. Try one more time: set the lower limit to 50dB, and increase the time window to at least 600ms. We are looking for the modal ringing to decay below 50dB. Keep increasing the time window until the waterfalls end at the bottom of the graph. Unless there is something wrong with the measurement, there is a serious problem.

Your right, it doesnt, but no amount of fiddling with it will make it better.

At the bottom of the problem is that I am not making the initial measurement with REW. I do not have a PC of any kind attached to my main system, therefore I cant produce their sine sweeps. My system is a one input affair, a CD player. So I would have to have the REW sweeps on a CD to be able to get around this. I have to use Dayton's Omnimic and export the IR wav file to REW.

Gear mentioned in this thread:

post #2852 of 9620
Quote:
Originally Posted by jim19611961 View Post

Your right, it doesnt, but no amount of fiddling with it will make it better.

At the bottom of the problem is that I am not making the initial measurement with REW. I do not have a PC of any kind attached to my main system, therefore I cant produce their sine sweeps. My system is a one input affair, a CD player. So I would have to have the REW sweeps on a CD to be able to get around this. I have to use Dayton's Omnimic and export the IR wav file to REW.

You'll get better signal to noise ratio when the sweep is louder and longer. Also check that your recording settings utilize the available dynamic range properly. Before exporting the IR, normalize it then export with the highest bit depth available.
post #2853 of 9620
Quote:
Originally Posted by AustinJerry View Post

the "target" is to have all frequencies (at least those >40Hz) decay below the noise floor by 300ms.

What about frequencies <40Hz?
post #2854 of 9620
Quote:
Originally Posted by markus767 View Post

You'll get better signal to noise ratio when the sweep is louder and longer. Also check that your recording settings utilize the available dynamic range properly. Before exporting the IR, normalize it then export with the highest bit depth available.

I have already done all that you mentioned except for normalizing before export. I may give that a try and see if there is a difference. Thanks.
post #2855 of 9620
Quote:
Originally Posted by markus767 View Post

What about frequencies <40Hz?

My thoughts are that modal ringing below 40Hz is very difficult to control (lots of big thick treatments), plus content below 40Hz is not that common, especially in the music that I listen to.
Quote:
Originally Posted by markus767 View Post

Typically only the first 40dB are useful in a waterfall graph, the rest is most often just noise. Always use REW's RTA to measure the noise floor. Helps a lot in interpreting the data correctly.

Markus, we discovered early in our use of USB mics that they are not capable of measuring below 50dB, so it is difficult to determine the true noise threshold with this mic. With my EMM-6, I was measuring a noise floor of 40dB. So, I have been using 50dB as the lower limit on the scale, and taking readings at 90dB. Do you have a better recommendation?
post #2856 of 9620
Quote:
Originally Posted by AustinJerry View Post

My thoughts are that modal ringing below 40Hz is very difficult to control (lots of big thick treatments), plus content below 40Hz is not that common, especially in the music that I listen to.

So you omit that range because it's hard to control? Measurements should reveal problems not cover them up. Nevertheless it is a viable solution to apply a high pass filter to speakers if really nothing else can be done about improving speaker position and acoustics.
Quote:
Originally Posted by AustinJerry View Post

Markus, we discovered early in our use of USB mics that they are not capable of measuring below 50dB, so it is difficult to determine the true noise threshold with this mic. With my EMM-6, I was measuring a noise floor of 40dB. So, I have been using 50dB as the lower limit on the scale, and taking readings at 90dB. Do you have a better recommendation?

A S/N ratio of only 50dB? That's pretty bad. Is that the UMIK-1?
post #2857 of 9620
Quote:
Originally Posted by markus767 View Post


A S/N ratio of only 50dB? That's pretty bad. Is that the UMIK-1?

No, it is the UMM-6 from Cross-Spectrum Labs. Although I understand the UMIK-1 has this same limitation. I believe these mics all use the same internal component. On the other hand, it's upper limit is ~115dB. I love taking measurements at 115dB! eek.gif

Edit: I believe we received confirmation from CSL regarding the 50dB S/N for the UMM-6, but I can't seem to locate the post.
Edited by AustinJerry - 5/17/13 at 3:06pm
post #2858 of 9620
They really need to improve those numbers...
post #2859 of 9620
Quote:
Originally Posted by markus767 View Post

They really need to improve those numbers...

Agreed. So, testing for understanding, with this S/N limitation, is it appropriate to set the lower limit for the waterfall to 50dB?
post #2860 of 9620


Here is a S/N graph of my mic I found on the web. As one can see, the actual S/N varies considerably with frequency. I assume to some degree, this is true of other mics as well.
post #2861 of 9620
Quote:
Originally Posted by AustinJerry View Post

I ran across some measurements that demonstrate my journey seeking good bass response in my listening room, and which also show the value of being able to use measurements to help the journey along.  Note also that I followed Keith's advice:  you can never have too much subwoofage....

First, two subs on the front wall, showing a poor placement that exacerbates a room mode at 58Hz (as determined by the Room Mode Calculator tool).




First improvement:  move the subs to the 1/4 and 3/4 spots on the front wall.  Notice how this movement tamed the peak at 58Hz (new location in blue).




Next improvement:  add two additional subs, placed on the back wall (front subs in blue, back subs in red).  Notice the difference in responses below 35Hz, and above 70Hz.




Looking at the combined response of all four subs, and how the combined responses below 35Hz and above 70Hz are now improved.




Add Audyssey room correction:




Now tweak the sub distances (only marginal improvement on my system):




So, here is a summary of the journey, showing the starting and ending response:



 
 




Nice breakdown, Jerry. Is the ability to set sub distances separately in your AVR helped you in this case?
post #2862 of 9620
Quote:
Originally Posted by Pres2play View Post

Nice breakdown, Jerry. Is the ability to set sub distances separately in your AVR helped you in this case?

Yes, it helps for the sub distance tweak.
post #2863 of 9620
Quote:
Originally Posted by jim19611961 View Post

Here is a S/N graph of my mic I found on the web. As one can see, the actual S/N varies considerably with frequency. I assume to some degree, this is true of other mics as well.

Not sure what the upper curves show. Just the preamp of the mic or mic + preamp + room?
Edited by markus767 - 5/18/13 at 1:32am
post #2864 of 9620
I'm new to REW and I'm trying to gain more knowledge on how to correctly use this software. So, excuse me if my questions have been already covered in previous posts (2,863 as of this moment).

The basics:

I'm using a Dell laptop with Windows 7 Pro 32 bit with HDMI output.
REW installed is 5.01 Beta 17
Mic is an OmniMic V2 with calibration file


My system is a 11.2 setup. I'm using a Denon 4311CI as pre/pro and I have external amps to drive the speakers. Here is the room that I'm working with:

Warning: Spoiler! (Click to show)


Yes, it is a very live room. And that is one of the main reasons I'm coming here for help in order to tame first reflections at the walls.


The questions:

OmniMic V2 calibration file - Do I need to change the extension of the calibration file from .omm to .txt? I can see that REW actually recognizes the .omm as a valid file. But, just wondering on an early post at this thread that was recommending to change the extension.

Room treatments - can someone explain or provide a link (easy to understand for a person that is just getting familiar with REW) on how to use identify the first reflections points at the walls?

As mentioned before, I do have a live room? First action for me is to buy a large and thick area rug to take care of the reflections out of the floor (I can't remove the coffee table as much as I wish ..........WAF).

I purchased a box of OC703 and pine wood to build my acoustic treatments. But, before going crazy and hanging them at the walls, I want to ensure they will be installed in the right place. Hence the reason I'm asking for some guidance/instructions.


Thanks in advance!
post #2865 of 9620
Quote:
Originally Posted by AustinJerry View Post

Agreed. So, testing for understanding, with this S/N limitation, is it appropriate to set the lower limit for the waterfall to 50dB?

Take a noise floor reading with the RTA. This shows how high the noise floor is at each frequency.
Look at the whole impulse response to get the time span after which the response decays into the noise floor. This reveals at what time the waterfall graph shows more or less just noise.
post #2866 of 9620
Quote:
Originally Posted by cr136124 View Post

I'm new to REW and I'm trying to gain more knowledge on how to correctly use this software. So, excuse me if my questions have been already covered in previous posts (2,863 as of this moment).

The basics:

I'm using a Dell laptop with Windows 7 Pro 32 bit with HDMI output.
REW installed is 5.01 Beta 17
Mic is an OmniMic V2 with calibration file


My system is a 11.2 setup. I'm using a Denon 4311CI as pre/pro and I have external amps to drive the speakers. Here is the room that I'm working with:

Warning: Spoiler! (Click to show)


Yes, it is a very live room. And that is one of the main reasons I'm coming here for help in order to tame first reflections at the walls.


The questions:

OmniMic V2 calibration file - Do I need to change the extension of the calibration file from .omm to .txt? I can see that REW actually recognizes the .omm as a valid file. But, just wondering on an early post at this thread that was recommending to change the extension.

Room treatments - can someone explain or provide a link (easy to understand for a person that is just getting familiar with REW) on how to use identify the first reflections points at the walls?

As mentioned before, I do have a live room? First action for me is to buy a large and thick area rug to take care of the reflections out of the floor (I can't remove the coffee table as much as I wish ..........WAF).

I purchased a box of OC703 and pine wood to build my acoustic treatments. But, before going crazy and hanging them at the walls, I want to ensure they will be installed in the right place. Hence the reason I'm asking for some guidance/instructions.


Thanks in advance!

 

Regarding basic acoustics information, there are a number of useful articles on the RealTraps web site here, as well as on the GIK Acoustics site here.  Both RealTraps and GIK are respected vendors of room treatment products, and both companies have acoustics consultants who will review your REW measurements and room pictures and assist you in making educated decisions WRT treatments.

 

Looking at the picture of your listening room (which, by the way is very attractive, with what looks like some fine equipment), there are a number of things that might warrant a closer look.  The wood floor is most certainly reflective, and the rug doesn't cover much of the area.  The coffee table surely directs reflections from the center speaker.  The bare wall behind the listening area should be an early focus of attention, and is easily treatable with either absorbtion or diffusion (or a combination of both).  We can only see one side wall, and the door looks to be in the center of the first reflection point.  Use the "mirror technique" to determine for sure.  And, of course, the ceiling could add unwanted reflections. 

 

So, looks like you have a raw canvas there begging for you to get started!  wink.gif  The most important advice I can offer is for you to take it slowly, measure and report your progress, seek advice, and enjoy the journey.  And, of course, make sure you coach your significant other during the process--you don't want WAF to become an issue (or is it SOFA--Significant Other's Factors of Acceptance?)

post #2867 of 9620
Quote:
Originally Posted by markus767 View Post

Not sure what the upper curves show. Just the preamp of the mic or mic + preamp + room?

The upper curves are the mic, the lower ones the pre amp

http://www.fritzsoundlab.com/info.html
Edited by jim19611961 - 5/18/13 at 8:13am
post #2868 of 9620
Quote:
Originally Posted by markus767 View Post

You'll get better signal to noise ratio when the sweep is louder and longer. Also check that your recording settings utilize the available dynamic range properly. Before exporting the IR, normalize it then export with the highest bit depth available.



This measurement was taken about 5db louder and normalized. It is a bit better. FYI, my main speakers and subs are both ported, and tuned in the 25-30hz range.
post #2869 of 9620
Quote:
Originally Posted by jim19611961 View Post

The upper curves are the mic, the lower ones the pre amp

How do we know that the graph shows just the mic and not the noise floor of the room/testing chamber?
post #2870 of 9620
Quote:
Originally Posted by jim19611961 View Post

This measurement was taken about 5db louder and normalized. It is a bit better. FYI, my main speakers and subs are both ported, and tuned in the 25-30hz range.

Could you post the IR as a soundfile?
post #2871 of 9620
Quote:
Originally Posted by markus767 View Post

How do we know that the graph shows just the mic and not the noise floor of the room/testing chamber?

I only know what the link explains.
post #2872 of 9620
Quote:
Originally Posted by markus767 View Post

Could you post the IR as a soundfile?

https://dl.dropboxusercontent.com/u/41391584/05%2018%20Left%2080db%20N.wav
post #2873 of 9620

What kind of room is that? There's a very strong reflection after 24ms?


Edited by markus767 - 5/18/13 at 9:10am
post #2874 of 9620
Quote:
Originally Posted by markus767 View Post

What kind of room is that? There's a very strong reflection after 24ms?

http://www.gearslutz.com/board/studio-building-acoustics/817205-my-listening-room.html
post #2875 of 9620
Ah! You're living in an anechoic chamber - that explains it smile.gif Now get the frequency response right and you can rent out your living room as a studio.
Edited by markus767 - 5/18/13 at 9:23am
post #2876 of 9620
Quote:
Originally Posted by markus767 View Post

Ah! You're living in an unechoic chamber - that explains it smile.gif Now get the frequency response right and you can rent out your living room as a studio.

unechoic chamber ?

What about the FR response needs addressing IYO ? (go to the very end of that thread to see my latest)

Or easier yet, here is my latest. (at listening position)(1/24th oct smoothing applied)


Edited by jim19611961 - 5/18/13 at 9:37am
post #2877 of 9620

Jim, I just read through your thread over on GS. Nice project, and fantastic room. You should be an example to those of us here who are struggling with coming up with a small room model. I am in awe!
post #2878 of 9620
Quote:
Originally Posted by markus767 View Post

Ah! You're living in an anechoic chamber - .

Not really.

Is that your read?

Its quite lively actually.
post #2879 of 9620
Quote:
Originally Posted by AustinJerry View Post

Jim, I just read through your thread over on GS. Nice project, and fantastic room. You should be an example to those of us here who are struggling with coming up with a small room model. I am in awe!

Thanks Jerry. (actually your only 2 hours away from me if you care to hear it)

Anyone is welcome to borrow from it, its not copyrighted, yet biggrin.gif

The approach philosophy is actually pretty simple.

1) Lots and lots of bass trapping.
2) Then add delayed reflections/diffusion targeted to arrive after 20ms to keep it from getting dead.

There are important details after this, but the above sums up the global view.
Edited by jim19611961 - 5/18/13 at 2:17pm
post #2880 of 9620
Quote:
Originally Posted by jim19611961 View Post

Its quite lively actually.

Is that what people say when they visit you?
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