Home Theater Forum and Systems banner

1 - 7 of 7 Posts

·
Registered
Joined
·
14 Posts
Discussion Starter · #1 ·
Hello All:

My goal is to understand how to use check levels correctly.

I have already a) calibrated my Scarlett 2i2 soundcard; b) loaded the calibration file for my Dayton EMM-6; and c) set my SPL output and input levels on my Scarlett 2i2 according to this article [1].

I can report the following anecdotal evidence. I set about executing the check levels procedure in preferences using the Subwoofer option. I turned the AV processor volume up to about -35dBFS when my wife came in from the kitchen to tell me the glasses were falling off the shelves at which point I stopped. Then the dog came in to investigate. She is old and we thought she was deaf.

The instructions here [1] direct me not to change the position of the gain on the test channel of the Scarlett 2i2 because it will affect the SPL sensitivity.

I am left with the impression that I could continue to increase either a) the volume on the AV processor; or b) the Sweep Level; or c) both to achieve some arbitrary volume that I can watch on the check levels input meter. Is there a minimum I have to reach? In addition to the volume, there was a very noticeable effect of a wind coming from the Subwoofer.

Could someone please explain how to execute check levels given these facts? More specifically, could you explain the documentation in the check levels window in relation to using a USB microphone with a sound card already calibrated to the proper SPL? The documentation reads as follows: "If you are using a USB microphone leave the volume control at the unity gain setting, which is selected by default when the mic is first plugged in." But, I don't any sense of what unity gain means in terms of the AV processor volume.

Sorry, I just don't have enough background to interpret the documentation. I am a software engineer and a guitarist.

Thanks in advance for your advice.

1. http://johnr.hifizine.com/2013/03/room-eq-wizard-spl-calibration-without-an-slm/

--
Rick
 

·
Super Moderator
Joined
·
9,280 Posts
Hey Rick,

There are at least a few instances in the process where levels are checked, such as when doing the loopback calibration, setting the soundcard sound card input levels, the SPL calibration routine (I assume you’re not talking about that one, given the link you’ve referenced), and before the actual in-room measurement. You don’t indicate in your post which of these you’re having problems with.

Regards,
Wayne
 

·
Premium Member
Joined
·
1,562 Posts
Rick,
Do you have the UMM6 (USB mic)or the EMM6 (XLR) mic? It is not clear which you have and it makes difference to the setup process.

[Also, be advised that there are no cases where the sound volume needs to excessively high for either the setup or measurement process so give the neighborhood and your speakers a break. :D No sound needs to be used for setup and volume should be adjusted to about 75dB for SPL testing.]
 

·
Registered
Joined
·
14 Posts
Discussion Starter · #4 ·
Thanks, Wayne. Apologies for not being clear.

The instance of check levels I am describing is not for the sound card calibration or the loop back input calibration for the SPL procedure described here [1].

I am just blindly following instructions in the Getting Set Up for Measurement chapter of the REW help file. Sorry, I just don't have enough context to interpret the information in the help file, yet.

The help file says "Setting the signal level REW uses during measurement involves generating a pink noise calibration signal and adjusting the AV processor's volume control and/or the calibration signal level so that at the measurement point (usually ear height at your main listening position) your SPL meter shows a level of around 75dB. The soundcard's input volume then needs to be adjusted to get a good signal level from the SPL meter or mic preamp when the cal signal is playing."

1. http://johnr.hifizine.com/2013/03/room-eq-wizard-spl-calibration-without-an-slm/
 

·
Premium Member
Joined
·
1,562 Posts
Thanks, I just wanted to be sure.
There are several methods to set the calibration of the REW internal SPL meter using the XLR mic.

The John Reekie method you linked does not require a handheld sound level meter (SLM) and instead requires a volt meter which you apparently have. That method creates no sound, and is a little more difficult to follow.

The REW setup info you reference uses a handheld SLM, or just estimates the 75db sound level setting based on using moderately loud pink noise, and then sets the internal REW SLM at 75dB. It is not critical if the level is not set real accurately because, for EQ use and most other common uses, we are interested in relative levels, not absolute levels.

The issue you had was that during your the REW SLM cal the 2i2 input level was set too low. Therefore, when measuring at 75dB sound level the input signal level is reported as very low (-75dB). It should be maybe someplace around -25dB. You should run through the cal process again to correct this. The 2i2 input level for the mic cal will be much higher than it was for the soundcard cal. It will probably be at about 80% to 90% of full input level. When you go through the process again make sure the headroom reported during the cal process is maybe around 100-105dB.

Which setup process do you want to repeat? The John Reekie method, or the REW method?

The REW method is easier and about as accurate if a handheld SLM meter is available. Some people are using an phone app for that. If no handheld meter is used the result is just an estimate of the SPL level, but that is all that is really needed anyway.

Either method is fine. Let us know if you still have trouble.
 

·
Super Moderator
Joined
·
9,280 Posts
Adding a bit to what John said, if you’re trying to get REW’s input meter up to something in the -12 to -24 dBFS range by raising the AVR’s volume, as instructed in the Soundcard “Help” window, and it’s getting so loud that the deaf dog can hear it, you can accomplish the same thing by increasing the mic input on the Scarlett. This will increase REW’s input while not changing the output to the system. Indeed, this is noted in the “Help” box that appears when the “Check Levels” button, then the ”Next” button is pushed: “If you are using a mic pre amp, the level control on it may need adjusting.”

Ultimately the level setting on input meters don’t matter much; as long as you have a signal that registers you're good. If you do, then go ahead and measure!

Regards,
Wayne
 
1 - 7 of 7 Posts
Top