Room EQ Wizard "In" and "Ref In"

[MITJABORKO]

I am using Apple MacBook Air, Behringer U-PHORIA UMC240HD USB audio interface, and Behringer ECM Microphone.

Could someone tell me please, what is the difference between "In", and "Ref In", and how could I select between two input options.

 

[John Mulcahy]

"In" is used to make measurements. "Ref In" is only used if a loopback is connected as a timing reference. The input used for measurement can be selected in the Soundcard preferences or, with the latest V5.19 beta, on the Measure dialog.

 

[MITJABORKO]

Thank you John for your prompt answer.
Using my Apple MacBook Air I normally used "IN, and "OUT" for my measurements, and I did not even care about "Ref IN", until yesterday. Until yesterday.
Yesterday I noticed that "IN" became inactive - the highest level in the measured input is just -641 dB SPL, and "Ref IN" became active, at -20dB generator level, I could easily set -35dB level at "Ref In", but I can not perform measurements anymore.
On Souncard preferences my "Input Device", and my "Input" settings are "Behringer U-PHORIA UMC240HD" ... so I do not understand at all what should be wrong ...
My Apple soundcard seems to work perfectly, I could listen to YouTube stereo sound for example without any problem ...
So, I do not understand what might have happened yesterday ...
So, my question is about, how to deselect "Ref IN", and how to select "In" on my Soundcard preferences?

 

[John Mulcahy]

In and Ref In are generally different channels of the same input, R and L, for example. Sounds like you just need to change the channel for In.

 

[MITJABORKO]

wow! John, I followed your advice, I changed to RIGHT, and it Works! Thank you very much indeed.

Now, I am facing with unexpected SPL calibration problem, where maximum SPL is 53 dB only. Consequently, when I measure the frequency response characteristic of the same test loudspeaker, the measuring result is comparable, however 1 kHz level which was at 120 dB SPL before, is only at 0 dB SPL now. All potentiometers are on the same positions as before. Any useful advice?

 

[John Mulcahy]

Just repeat the SPL calibration process, but remember that the figure you enter is from your own external SPL meter, it is NOT the figure on the REW meter. If you don't have an SPL meter just make sure the test signal is at a comfortable level and enter 75 dB.

For measurements you have already made you can shift the graph using the Offset adjustment in the graph controls. Adjust the value until the graph is at the level you want then click the Add to Data button.

 

[MITJABORKO]

Another excellent answer! Thank you John!
Of course I have a small Radio Shack SPL meter too and calibration is OK now. Actually so simple.
But ... it must be Murphy ... additonal problem arose ...
The frequency sweep seems to be normal from 20Hz to 20kHz, also the loudspeaker response seems to be regular from 20Hz to appr. 3kHz, where sharp cut-off occurs instantly, droping down to the noise level ??? Could it be some kind of de-sinchronization, or what ? ...
P.S.. In a moment I do not use any EQ, or MIDI.
Best regards, Mitja.

 

[John Mulcahy]

That can happen if there is a long buffering delay in the replay path - REW stops capturing the response before it has been completed, so the HF part gets cut off. The easiest way to deal with that is to select "Use acoustic timing reference" at the top of the Measure dialog and tick the "Wait for timing reference" box under the "Start measuring" button.

 

[mattel]

Hi John,
Newbie here. I just ran my first set of measurements. It is a little overwhelming so I am back tracking to try to understand all the REW configurations. Starting with How do I determine which timing reference to use; loopback or acoustic? Is acoustic preferred when using HDMI? Is there a tutorial that explains the pros and cons?

Thanks