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Discussion Starter · #1 ·
Hello everyone,

I'm new to REW and these forums. I have read a few guides on this forum on the topics of for instance what hardware to use for REW and about the hard knee house curve. There is one issue that I'm having that I have not seen mentioned in other threads so that's why I'm making this post.

Let me start off with the hardware that I'm using:

Behringer UCA-222 external USB soundcard for usage with my laptop
Behringer Xenyx 802
Behringer ECM8000 mic (with cal file from these forums)

Emotiva UMC-200 preamp
Emotiva XPA-5 amp

The problem that I have is that after I check the levels in REW and adjust the measured volume to be roughly the same as the output (by adjusting both the mic preamp on the Xenyx and volume on the UMC-200), the measurements always clip. I get 0 headroom and the warning message. If I lower the volume on for instance the UMC-200 then I can get rid of the clipping. But doing so doesn't make sense to me, since I just checked the levels before. Can anyone make any sense of this and help me figure out what is going on?

Another issue I'm having is that when everything is hooked up I'm getting some "digital noise" over the speakers. I'm guessing this has something to do with earthing and where the cables are, there are plenty of unbalanced connections so it's not strange this can happen. Not too fussed about it, but I'm guessing this influences the measurement as well, since it's not only the sweep being measured but also these "digital blips and bleeps"?

Thanks for reading! Greetings from the Netherlands. :wave:
 

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The leveling of the volume is a step in the calibration process for the UCA-222. Once that process is completed and the loopback cable is removed then the process is complete.

The next process is the calibration of the REW SPL meter and assuring that reasonable mic input headroom is set. The UCA-222 mic input level is adjusted as needed until the headroom is target is reasonable. Once that is completed REW is ready to make measurements.

Measurements should be at an SPL level around 75 dB. This can just be adjusted with the UMC-200 volume control. The reported mic input level during a measurement will be significantly less than the output level. With a -12 dB output level and my pre-pro volume adjusted to provide 75 dB at the LP, my input level is reported by REW to be -18 to -24 dB. Your numbers may be a little different. [Just offering typical numbers to provide some sense of what to expect.]

Regarding "digital noise":
This is may be PC power supply noise leaking into the audio channel? This problem is very often PC model dependent. My original ASUS notebook PC had this problem. My current HP notebook does not. The Asus noise was eliminated when running on battery power or when using a cheater plug on the power supply. You may want to try battery power and see if that corrects the problem. A cheater plug is considered to be a safety hazard in the USA so it is not advised here.
 

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Discussion Starter · #3 ·
Thanks for your post. My conclusion is that I was doing something wrong. I was checking the levels under preferences with the loopback already removed. So I made the calibration for the UCA-222, removed the loopback and checked the level. As I understand now I need to remove the loopback after checking levels, I will try that later this upcoming week.

The typical signal levels also help, gives me something to use as a reference.

Unfortunately my laptop's battery only lasts for about a minute nowadays, so I cannot go without the power plug. Cheater plugs are also not permitted over here :) I'll see what I can do, but I don't really see any solution at this point.

I'll come back here after I've tried the level checking again and have done some measurements.
 

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Discussion Starter · #4 ·
Hmmm I think I was doing it right after all.

So I made the calibration for the UCA-222 external soundcard. Then in preferences I press check levels and I choose Use Main Speaker to Set / check levels. Then I need to set this for -18 dB according to the help text. I managed to do this by changing the volume on my preprocessor.

I have everything hooked up as described in this thread: http://www.hometheatershack.com/for...ards/10001-rew-cabling-connection-basics.html. But there is one strange thing going on here. I'm seeing input on the left channel too while I'm using the right channel... I took a screenshot, anyone have a clue what's going on?

When I now do a measurement, there is just enough headroom (around 0.5 dB). That is still a bit of a surprise after checking levels and setting it to -18 dB FS....
I also see both L + R inputs jump around when running multiple sweeps in between the sweeps... :dumbcrazy:
 

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Do you have the monitor switch on the UCA-222 set to "off"?
Similarly, any monitor function on the 802 also needs to be set to "off".
 

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Discussion Starter · #6 ·
Thanks for your reply.

I have that monitoring button set to off. I did find out from this thread: http://www.hometheatershack.com/for...solutions-calibration-rew-windows-7-more.html that setting the output device and output and input device and input to SPEAKER and MICROPHONE decreases the readings in the left channe to around -70 dB. I'm seeing something similar in that thread, so I guess this is normal with the UCA-202 / 222 soundcards.
 

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Did you also check that 'Listen to this device' is not checked on the Listen tab of the Recording Devices properties for the UCA input?
 
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