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Simplified REW Setup and Use (USB Mic & HDMI Connection) Including Measurement Techniques and How... - Page 135

post #4021 of 9584
Quote:
Originally Posted by AustinJerry View Post


Edit: Since determining the noise floor is a topic that comes up repeatedly, can you help me draft a simple instruction that can be included in the guide? I already have a brief discussion of noise floor in the section on mic calibration? Does this section need some re-wording? Any help would be appreciated.

Great idea and I hope you and Markus will do that. Even after reading several specific posts on the topic I am still a bit unsure on EXACTLY how the test should be set up and ran. I am getting around 26-30 dB based on how I ran it (in a well isolated room) but would like to make sure I'm doing it correctly (just SPL Meter, SPL meter and logger, combine with RTA etc).

Edit: Here's an example of what has me confused. I just did a reading as shown below with both the spl logger and RTA running.
You'll see that the spl logger and meter reflect around a 43 dB level, while the RTA (with spectrum chosen) only registers close to 30dB at the highest. Why do these not track each other and which should be used?
Seems to me that if my mic is hearing something at 43dB that same information should be showing up somewhere in the frequency spectrum in RTA.


Edited by fotto - 7/13/13 at 8:04am

Gear mentioned in this thread:

post #4022 of 9584

I did a search in this thread and several others for the term "noise floor".  AFAICT, the basic procedure is to open the REW RTA tool, click the red button, and look at the value displayed in the small RMS window to the left of the red button.

 

 

If there is more to the procedure, I hope Markus or another expert will expand on it.  Of course, the accuracy depends on this input source, either a basic SPL, or a calibrated mic.  And on the sensitivity of the input device as well.  The USB mics are showing a fairly poor sensitivity, showing on average noise floor readings in the neighborhood of 50dB.

post #4023 of 9584

REW Guide Version 2.85

 

A new version of the REW guide has been posted.  Changes included in this revision:

 

 

2.85

July 7, 2013

  • Added section “UMIK-1 Microphone:  Special Considerations”.

 

 

The Guide and be downloaded from the link in my signature.  Comments on how to improve the guide, or what new topics should be included, are always welcome.

post #4024 of 9584
Quote:
Originally Posted by fotto View Post




Edit: Here's an example of what has me confused. I just did a reading as shown below with both the spl logger and RTA running.
You'll see that the spl logger and meter reflect around a 43 dB level, while the RTA (with spectrum chosen) only registers close to 30dB at the highest. Why do these not track each other and which should be used?
Seems to me that if my mic is hearing something at 43dB that same information should be showing up somewhere in the frequency spectrum in RTA.

 

 

I am getting somewhat different results.  The 48dB value in the logger is quite close to the 50.7dB value in the RMS window of RTA.  I don't know why your values are so much different, and a value of 66.6dB for your RTA seems a bit high.

 

 

 

Edit:  Could be the lower limit you are using for RTA.  Adjust the left limit on the horizontal scale as low as it will go.  Many times the high noise floor is caused by sub-sonic noise below 20Hz.

post #4025 of 9584
Yeah doesn't seem right...I'm going to take another run at it as something's amiss. I found a thread over at HTS where John explains the RTA in some detail that might help explain. Take a read and let us know what you think: RTA
Here's another: Noise floor
post #4026 of 9584
Quote:
Originally Posted by jim19611961 View Post



(reading taken with no sweep generation) (see the bump at 59hz? The refrigerator)

Using RTA, one can see that although the average says 48.5db, the actual readings vary by almost 40db from low to high frequencies.

But yes, their should be consistency unless their are imposing noises from outside like cars driving by, air conditioning and refrigerators turning off and on, and so on.

Quote:
Originally Posted by AustinJerry View Post

I did a search in this thread and several others for the term "noise floor".  AFAICT, the basic procedure is to open the REW RTA tool, click the red button, and look at the value displayed in the small RMS window to the left of the red button.




If there is more to the procedure, I hope Markus or another expert will expand on it.  Of course, the accuracy depends on this input source, either a basic SPL, or a calibrated mic.  And on the sensitivity of the input device as well.  The USB mics are showing a fairly poor sensitivity, showing on average noise floor readings in the neighborhood of 50dB.

Something odd about those huge spikes. I use a USB mic and I am not getting these. Especially odd how they fall exactly at 2k, 3k, 4k, and so forth.
post #4027 of 9584
Quote:
Originally Posted by AustinJerry View Post


Edit:  Could be the lower limit you are using for RTA.  Adjust the left limit on the horizontal scale as low as it will go.  Many times the high noise floor is caused by sub-sonic noise below 20Hz.

Hmmm...I think you nailed it on the head. Take a look at a new reading with down to 2 hz exposed. So if that's in the total then it makes sense why it's so high.



post #4028 of 9584
Quote:
Originally Posted by AustinJerry View Post

Thanks for posting these, Murray. So we can understand the measurements, these represent left+right+subs, correct? And where are the measurements taken, in the center seat of each row, with the mic placed at your ear height as if you were sitting in the seat?

The waterfalls show worse ringing in the 40Hz region for the back row. Ringing for the front row is worse in the 70Hz range. It is not surprising that there are different bass issues across the three rows. Given the three tiers, it is expected.

Refresh my memory, do you have bass treatments in your theater? I think you could benefit from additional bass trapping. And the measurements you posted are for one placement of the subs. The original objective was to experiment with different placements to find the best one. Do you still plan on moving things around and using your new REW skills to find the best positions?

And I hope you are still having fun!

Yes they are L+R+Subs, all from the centre postion of each row. Mic at ear height.

I have lots of bass traps up and around the back row, I worked with Ethan on designing these.

I don't mind moving the 4 front subs anywhere along the front wall but I cant move them any other place, there are side aisle and stairs. The back subs will be placed under the floor in the back row, currently they are sitting on the floor infront of the two outer seats, if they needed to move they can only go to the two inner seats.
post #4029 of 9584
Quote:
Originally Posted by RapalloAV View Post

Yes they are L+R+Subs, all from the centre postion of each row. Mic at ear height.

I have lots of bass traps up and around the back row, I worked with Ethan on designing these.

I don't mind moving the 4 front subs anywhere along the front wall but I cant move them any other place, there are side aisle and stairs. The back subs will be placed under the floor in the back row, currently they are sitting on the floor infront of the two outer seats, if they needed to move they can only go to the two inner seats.

Sounds like you are done with the positioning exercise, then. I think the waterfalls look pretty good, and if I recall, you seem to be pretty pleased with the results. More traps might improve things a bit, but if you don't have any more room, that's that.

One other graph might be interesting to look at is the Decay graph. You can produce it from the same measurements you already have. The instructions are in the guide. Generate the graph, remove all the slices except the one at 160ms, and look for the gap between the primary slice and the 160ms slice. The objective is to have all bass resonances decay by at lease 20dB in the first 160ms. This graph makes it very easy to see if you meet this objective across all frequencies up to 100-150Hz.
post #4030 of 9584
Quote:
Originally Posted by AustinJerry View Post

Sounds like you are done with the positioning exercise, then. I think the waterfalls look pretty good, and if I recall, you seem to be pretty pleased with the results. More traps might improve things a bit, but if you don't have any more room, that's that.

One other graph might be interesting to look at is the Decay graph. You can produce it from the same measurements you already have. The instructions are in the guide. Generate the graph, remove all the slices except the one at 160ms, and look for the gap between the primary slice and the 160ms slice. The objective is to have all bass resonances decay by at lease 20dB in the first 160ms. This graph makes it very easy to see if you meet this objective across all frequencies up to 100-150Hz.

Jerry, you might remember I have the two front side walls tapering to the screen a small amount. You gave me two graphs for front sub placement, one with the taper and one without. Based on my waterfall graphs do you think the sub position still stands up front?

I really want the front subs anywhere along the front wall (no sides) and the two up the back can go anywhere along the row of back four seats. There are restrictions for placement in the room due to stairs, aisles, doors etc etc...
The front screen wall is free to use any placement and the back row the two subs can be anywhere under the four seats.

How do subs at the back perform if they are up high, wall mounted?


post #4031 of 9584
Quote:
Originally Posted by RapalloAV View Post

Jerry, you might remember I have the two front side walls tapering to the screen a small amount. You gave me two graphs for front sub placement, one with the taper and one without. Based on my waterfall graphs do you think the sub position still stands up front?

I really want the front subs anywhere along the front wall (no sides) and the two up the back can go anywhere along the row of back four seats. There are restrictions for placement in the room due to stairs, aisles, doors etc etc...
The front screen wall is free to use any placement and the back row the two subs can be anywhere under the four seats.

How do subs at the back perform if they are up high, wall mounted?



Quote:
Originally Posted by RapalloAV View Post

I don't know whats up with this site but Im having trouble trying to add images to the same post, here are the rest.rolleyes.gif





Looking at the frequency response graphs you posted several days ago, there is a serious issue in what looks like the 55-65Hz range. This issue exists on all three rows.

Based on the Harman approach, you should place subs in the nulls associated with the peaks you are seeing. Unfortunately, the mode calculator shows a 61Hz mode associated with the room length. The advice would be to place subs at the 1/4 and/or 3/4 points along the side wall. However, you say that this placement is not acceptable.

There is a 58Hz mode associated with the room's height. By placing one or more subs at the mid-point of the rear wall's height might alleviate this null. If there is a way to elevate the subs temporarily and take some measurements, that would be something you might consider.

Will you have a chance to post the Decay graphs?
post #4032 of 9584
Jerry, you need to look at these freq response graphs I did yesterday, these are the "new" correct ones. The ones you just posted are the 1st experiment which don't apply now.

I will do the decay graphs for you shortly.




post #4033 of 9584
Hard to read, Murray. If we are focusing on the bass, publish only the 15-300Hz range, no smoothing.

What do the different color lines represent?
post #4034 of 9584
Better yet, do you have an account on a file-sharing service like Dropbox.com so that you can upload the REW measurement file? Rather than keep telling you that the graph format is not to my liking, it would be easier for me to take your measurements and analyze them on my computer.

If you need instructions for using Dropbox.com, let me know. Perhaps I should include the instructions in the Guide?

Presenting graphical data in a method that highlights the message you are trying to convey is not always easy!
post #4035 of 9584
Quote:
Originally Posted by AustinJerry View Post

Better yet, do you have an account on a file-sharing service like Dropbox.com so that you can upload the REW measurement file? Rather than keep telling you that the graph format is not to my liking, it would be easier for me to take your measurements and analyze them on my computer.

If you need instructions for using Dropbox.com, let me know. Perhaps I should include the instructions in the Guide?

Presenting graphical data in a method that highlights the message you are trying to convey is not always easy!

Jerry that would be much easier, you can then see everything you need. What do I have to do for using Dropbox?
post #4036 of 9584
1. Sign up for an account at Dropbox.com.
2. Install the Dropbox software on your laptop.
3. Drag the REW file to the Dropbox folder on your laptop, which will automatically load the file to your Dropbox account.
4. Log onto the Dropbox web site and browse to your "Public" folder.
5. Right-click on the REW measurement file and select "Copy public link".
6. Post the pub link here so I can access it.
post #4037 of 9584
Quote:
Originally Posted by RapalloAV View Post


Lets see if this works for you?
https://dl.dropboxusercontent.com/u/8646227/REW%20V5.lnk

 

No, that is not a good link.

 

Here is what an REW file looks like on dropbox.  Note that it is a MDAT file

 

 

Right-click and select Copy Public Link.

 

 

Here is the link:

 

Here is what the link should look like (Note MDAT file extension):

 

https://dl.dropboxusercontent.com/u/78476446/ULF%20ANALYSIS.mdat

post #4038 of 9584
Quote:
Originally Posted by RapalloAV View Post


How do subs at the back perform if they are up high, wall mounted?

Wall mounted subs!!! I can see myself mounting the JLAudio F113 on the walls smile.gif
post #4039 of 9584
Can someone help me figure out why I can't get asio to work? I followed the usb & hdmi guide but I'm stuck in that the mic is not active under the asio control panel.

In REW preference>sound card, I'm able to choose asio and the output selection is a generic hdmi. The input selection is also a generic hdmi which I find odd because if I choose java instead of asio, you can choose umm-6.

When I first start rew up it does recognize my umm-6 mic and asks me if that is the one I'm to use.
post #4040 of 9584
Ok, here we go anyone lives in Southern California who could teach me REW! I would love to learn from a master, then that teacher could experience a 7.2 movie with (3) B&W 800D2, (4) 802D1, (2)JLAudio Fathom F113, and a 10 feet wide 2:35 Stewart Film Screen with a JVC RS-35U

If interested please PM me smile.gif
post #4041 of 9584
Quote:
Originally Posted by jim19611961 View Post


Something odd about those huge spikes. I use a USB mic and I am not getting these. Especially odd how they fall exactly at 2k, 3k, 4k, and so forth.
That is a problem with the cheap USB mic. See my post way back in this thread: http://www.avsforum.com/t/1449924/simplified-rew-setup-and-use-usb-mic-hdmi-connection-including-measurement-techniques-and-how-to-interpret-graphs/1170#post_22958160. They said they would look at it but I never heard back. It is not a problem though given the amplitude of typical test signals.
post #4042 of 9584
Quote:
Originally Posted by DotJun View Post

Can someone help me figure out why I can't get asio to work? I followed the usb & hdmi guide but I'm stuck in that the mic is not active under the asio control panel.

In REW preference>sound card, I'm able to choose asio and the output selection is a generic hdmi. The input selection is also a generic hdmi which I find odd because if I choose java instead of asio, you can choose umm-6.

When I first start rew up it does recognize my umm-6 mic and asks me if that is the one I'm to use.

It is hard to say what is going on with your ASIO. In my experience, it can take a bit of effort to get ASIO to recognize everything. By effort, I mean stopping and re-starting REW, rebooting the laptop, and toggling back and forth between ASIO and Java. If you still have no success, REW is normally completely functional using the Java drivers. The only thing you can't do is select the surround speakers for measurements, and who needs to do that?
post #4043 of 9584
Quote:
Originally Posted by wse View Post

Ok, here we go anyone lives in Southern California who could teach me REW! I would love to learn from a master, then that teacher could experience a 7.2 movie with (3) B&W 800D2, (4) 802D1, (2)JLAudio Fathom F113, and a 10 feet wide 2:35 Stewart Film Screen with a JVC RS-35U

If interested please PM me smile.gif

The REW Guide contained in this thread is specifically designed for novice REW users like yourself. I almost titled it "REW for Dummies", but didn't want to offend anyone. Have you tried walking through the Guide?

Very nice equipment, by the way!
post #4044 of 9584
Quote:
Originally Posted by AustinJerry View Post

REW Guide Version 2.85

A new version of the REW guide has been posted.  Changes included in this revision:







2.85

July 7, 2013
  • Added section “UMIK-1 Microphone:  Special Considerations”.


The Guide and be downloaded from the link in my signature.  Comments on how to improve the guide, or what new topics should be included, are always welcome.



AJ,

Have you acquired and set up the UMIK-1 microphone yet? If so, what are your impressions of this mic? confused.gif


...Glenn smile.gif
post #4045 of 9584
Quote:
Originally Posted by Glenn Baumann View Post

AJ,

Have you acquired and set up the UMIK-1 microphone yet? If so, what are your impressions of this mic? confused.gif


...Glenn smile.gif

Functionally, I find it equivalent to the UMM-6. Physically, it seems to have a bit sturdier construction. You may have seen in an earlier post that my UMM-6 snapped in half when I dropped it. The UMIK-1 has a sturdier barrel construction which may prevent a similar mishap in the future. Other than that, I think either mic will serve perfectly well for REW purposes.
post #4046 of 9584
Quote:
Originally Posted by amirm View Post

That is a problem with the cheap USB mic. See my post way back in this thread: http://www.avsforum.com/t/1449924/simplified-rew-setup-and-use-usb-mic-hdmi-connection-including-measurement-techniques-and-how-to-interpret-graphs/1170#post_22958160. They said they would look at it but I never heard back. It is not a problem though given the amplitude of typical test signals.

So, not a USB problem per say, but a mic quality issue then?

The USB mic I use I dont consider a pricy one. So much difference?
post #4047 of 9584
Quote:
Originally Posted by jim19611961 View Post

Quote:
Originally Posted by amirm View Post

That is a problem with the cheap USB mic. See my post way back in this thread: http://www.avsforum.com/t/1449924/simplified-rew-setup-and-use-usb-mic-hdmi-connection-including-measurement-techniques-and-how-to-interpret-graphs/1170#post_22958160. They said they would look at it but I never heard back. It is not a problem though given the amplitude of typical test signals.

So, not a USB problem per say, but a mic quality issue then?

The USB mic I use I dont consider a pricy one. So much difference?

 

This issue has been raised before.  I believe the first mention of it was here BICBW.  I also seem to remember Herb from CSL commenting something about it but not sure if that was on AVS or HTS or maybe that was just about the higher noise floor?!  In any case, I seem to recall the consensus being that it was related to all USB mics and didn't introduce anything significant wrt REW measurements.  HST, if someone has updated info then I would be interested to here about it.

 

EDIT:  First mention was in the post above.

post #4048 of 9584
Quote:
Originally Posted by AustinJerry View Post

The REW Guide contained in this thread is specifically designed for novice REW users like yourself. I almost titled it "REW for Dummies", but didn't want to offend anyone. Have you tried walking through the Guide? Very nice equipment, by the way!

Have not, I will buy a microphone and try it out, I know you recommended two microphones but if you had to prioritize them which would you pick I don't mind paying a bit more and have better quality!
post #4049 of 9584
Quote:
Originally Posted by wse View Post


Have not, I will buy a microphone and try it out, I know you recommended two microphones but if you had to prioritize them which would you pick I don't mind paying a bit more and have better quality!

 

As I said earlier, now that I have owned both, I do not see a functional difference between them.  Early on, only the UMM-6 was sold by Cross Spectrum Labs with custom calibration files, so it was the recommended mic.  CSL sells both mics now, and both have custom calibration files.  Either mic will do nicely.

post #4050 of 9584

There are no ASIO files for the mac?

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