Originally Posted by AustinJerry
OK, I just ran my own tests, with these results:
With AVR MV at -13, playing the Speaker Level pink noise test tone from the REW Generator at -12dBFS, the REW SPL meter registers 90dB, and the level indicator below the meter reads -16dBFS input signal level. Note that the AVR was in Stereo mode, and I was outputting the test signal to both left and right speakers simultaneously. And also note that my sensitivity parameter is 6.352. With these settings, I can measure up to a 103dB signal without clipping.
I also opened up my UMIK-1, and the dip switches are set to On-Off-Off, or 100, which is -12dB, according to the table on the mic's PCB. Matt, I recommend you open the UMIK-1 just to make sure your dip switch settings are the same. If your settings are the same, I am not sure what to recommend next. BTW, I have seen reference else where that some computers have a "Microphone gain setting" in the Windows Recording Device properties. You might want to check if you have such a setting and, if yes, make sure it is set to off. The Guide doesn't refer to a gain setting because I have never seen one on any of my computers.
I replicated your setup and got about 88-89 db for pink noise with avr mv set to -13. I also went to stereo with front l and r playing the sound during the sweep. clipped again. next, I tried changing the mic volume from 100 down to 50 in the recording devices setting. when I test the level before running the sweep, it says "level ok" and it's -13.8db when the mic volume is at 100. if I turn the mic volume down to only 50 and hit "check level" in the measurement screen, it tells me "level ok" and it changes to -20.6. when I change the mic volume to 25 and check the level, the input goes down to -26. so the mic volume setting does seem to change the reading. I also get the same spl measurement of 88db with pink noise on the spl meter when the mic volume is at 50 or 100, but then the spl reading goes up to 89db when the mic volume is at 25 or even at 1.
Now, When I run the same sweep at the same 88db, I now have 3 db of headroom and it doesn't clip with the 50 mic volume setting. When I run the sweep again with the mic at 25 for the volume setting, I now can run the 88db sweep and have 8.8 db of headroom! This is sooo weird! Interestingly, the graphs don't seem to change much between the 100, 50 and 25 mic volume settings (attached).
Any thoughts at this point? it seems the mic volume level being turned down significantly will allow the input to not clip as easily. Is this a "band-aid" for a bigger issue? I also checked and have no way to control the microphone gain. I am running windows 7 on a dell laptop that's about 5 years old. thanks everyone for your help so far!!!
I also tried setting the mic volume to 0 and now the spl meter reads only 74 db but my rat shack reads 87-88 still (avr mv still at -13). It looks like as long as I have the mic volume setting to at least 1, the spl meter remains accurate (agrees with the rat shack) at about 88-89 db when the avr mv is at -13. This is really weird.....