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Adjusting input gain after calibration

2K views 4 replies 3 participants last post by  joeroe7 
#1 ·
First time trying to run REW. Sorry if this is a dumb question but my time is limited and I have spent countless hours trying to figure this out with no luck. After calibrating my sound card I am having problems getting 75db without either adjusting the input gain on my focusrite 2i2 or using the headphone jack and gain knob as the output to my avr. I thought I read somewhere that adjusting the input gain on my focusrite after calibration was a no no but the measurements after doing so seem to be good and consistent. The sound-card sweep looks good but then again I'm a newb so who knows.

Here is what I've been doing.

Calibrate with a xlr-trs loop back on Chanel 2 with phantom power on and all looks good. I have read that a trs-trs with phantom power off would be better for calibration when doing certain measurements.

REW settings

Right channel
Input 1.0
Sweep level -10
Output volume .5
Wave volume 1.0

I also have it set to have a loopback for time reference and do the loopback on channel 1 during measurements.

Focusrite settings

Input knob 1/2
Monitor 1/2

sound card sweep results

Level check 23.3 db
Headroom 9.8 db

After doing the calibration I use my spl meter to calibrate the REW spl meter to 75db. After this I do a level check and am nowhere near 75db unless I turn up the right channel input gain or crank the avr up 100% and that can't be good for measurements.

Have I been wasting my time trying to avoid adjusting the input gain after calibration? Any help you can give will be appreciated. I need to figure out where I am going to put my sub woofer so I can install the drywall and dead vents on the backside of my wall. The wife is complaining about the stack of drywall in the basement. I want to have a happy wife so please help!!!

Thanks
Joe
 
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#2 ·
There are 2 calibrations, a loopback calibration for the soundcard to allow its response to be calibrated out and ensure there is no feedback/monitoring, and a level calibration for the SPL meter. The meter level calibration is done with your mic plugged into the soundcard, and you should adjust the input gain to suit the mic before you do the level calibration. If you have a need to change the input gain after that just repeat the level calibration.

It doesn't really make sense to say you are "nowhere near 75 dB on a level check" after you have done the level calibration - if the AV was producing a signal that made your own SPL meter read 75 dB and you then tell REW that the signal it is seeing from the mic corresponds to 75 dB, the REW meter will then read 75 dB the same as your external meter. So how could you be nowhere near 75 dB when you should already be at 75 dB to have done the level cal in the first place?
 
#3 ·
It doesn't really make sense to say you are "nowhere near 75 dB on a level check" after you have done the level calibration - if the AV was producing a signal that made your own SPL meter read 75 dB and you then tell REW that the signal it is seeing from the mic corresponds to 75 dB, the REW meter will then read 75 dB the same as your external meter. So how could you be nowhere near 75 dB when you should already be at 75 dB to have done the level cal in the first place?
Sorry about that. I was in a rush when typing my post. You are correct, I am at 75db after the spl calibration but when I do a level check the reference in is good and the input is way too low. Sounds like adjusting the input gain after a soundcard calibration is fine as long as I calibrate the SPL meter with those settings. If that is the case I think all is good.

I am also having issues with REW (the latest version) intermittently not seeing my soundcard but this never happens when in preferences. Only when using the measurement function. It takes quite some time for the no soundcard input data window to pop up and when it does I click OK and everything works after that. I'm debating on bringing my Mac mini into the room and eliminate this 32 bit Windows 7 laptop.

Thanks for taking the time to answer a semi incoherent question posted by a person that may have seemed like an idiot. Today and yesterday have been pretty chaotic so my posts are very rushed. My wife will be back home tomorrow and I will have more time to play around with this awesome program and maybe even post a well thought out question.

Thanks
Joe
 
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