# Calibration Problem



## SamSpade (Jun 3, 2010)

Here is my latest problem. When I start to make a measurement, I open the panel that reads “Make a measurement.” I then click on “Check Levels,” and get a message “Level is low, -28.7dB.” After clicking on “Start Measuring,” I do get the various response graphs, but I don’t have confidence in the measurements because of the warning message.

My setup is: a calibrated Behringer ECM8000 connected to a Behringer 502 preamp. The preamp is connected to the SoundBblaster 24 bit Live! External card. The SB card is connected via USB to my laptop that is running Windows 7. The output of the SB card is connected to an input on my Lexicon MC-12 processor. The sound card has been calibrated and the mic calibration has been put into a file that is used by WAV.

My next step was to follow the “Check Levels Procedure.” I selected the Soundcard menu from the Preferences option. I then clicked on “Check Levels.” The Sweep Level is set at -12dB FS. Wave Volume is set at 1.000, and the Output Volume is set to 0.500. I also selected the “Use Main Speaker to Check/Set Levels.”

Then, I clicked on “Next” and heard the pink noise coming from my right speaker. I adjusted the volume control on my audio processor until my Radio Shack SPL meter read 75dB at my listening position (my Lex was adjusted to -18dB to achieve this SPL). Looking at the Right vertical bar meter, I adjusted the “Main Mix” gain of the preamp until the blue number at the top of the bar meter read -18dB.

Finally, I calibrated the SPL reading. After selecting the Mic/Meter tab, I unchecked the “C Weighted SPL Meter” box. I chose to use the “REW speaker cal pink noise.” Then, I clicked on the “Calibrate SPL” box and heard the pink noise play through my right speaker. Because I had already adjusted to volume of the audio processor to read 75dB at my listening position, I didn’t have to change the “75dB” reading in the “SPL Reading Calibration” box. So, I clicked on the “Finished” button.

Finally, I opened the “Make a Measurement” window. First, I clicked on the “Check Levels” box. Here is where I got the warning message: “Level is low -28.7dB.”

Where have I gone wrong to get this warning message?

Thanks for your help.


----------



## JohnM (Apr 11, 2006)

SamSpade said:


> I adjusted the “Main Mix” gain of the preamp until the blue number at the top of the bar meter read -18dB.


The number at the top of the bar is the peak reading (also the red line above the bar), the number at the bottom is the rms reading (the level of the bar) which is the one to aim for -18dB. Peak is about 10dB above rms for pink noise, hence the -28 or so you saw when making the levels check. The measurements will still be fine, but there is a small penalty in signal-to-noise so ideally it would be best to recalibrate so that the rms is around -18dB.


----------



## SamSpade (Jun 3, 2010)

Thanks for the quick reply. I will recalibrate per your directions.


----------

