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Discussion Starter #1 (Edited)
Maybe as a newbie I am aiming too high? Running OS X on a Mac Book Air equals only one USB input. That one is currently occupied by the M-Audio Fast Track Pro and attached to that the Behringer ECM 8000 microphone.
I have calibrated the sound pressure to 75db with my Sound Level meter and so far it is all sweet. When I do the last check levels prior to running the measure it tells me that the levels are too low? I think it could be because that there is a delay of the sound as I am running the test tone through Airfoil to the Aiport Express and then to the sound system. If I Ignore that and go onto measuring and I do get a chart but is is still saying that the level are too low as at the same time saying that some distortion and clipping has occurred. Maybe wireless Airfoil connection does not work and I need a Mac with two USB slots? M-Audio in and Sound out to the music setup? Any suggestions or ideas as getting another computer will be a bit of a hassle.
 

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The fast track pro has all the audio I/O you should need, it would be better to use it for output and input if you can. As a minimum it would be worth trying to do a loopback measurement with the M-Audio to make sure the input is working properly - it may not be, the latest apple Java update broke audio input from 4-channel soundcards, if the Audio Midi panel offers a 2-channel mode for the card that may fix things. A possible alternative if the input will not work would be to run under Bootcamp and try the Windows version of REW.
 

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Discussion Starter #3
Wow, that was a fast response! Maybe too fast for me to follow? Using the M-Audio for both input (microphone) and output? How would the output work as I use digital out (Airport Experss) to the Behringer DCX 2496 Ultra Drive Pro? I can see that the microphone is registering as "live" levels in the input looking at the sound setup. When I did not use the Java but ll default for in and out I did not get any input levels...
 

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Sorry, didn't realise you had the Airfoil on the output of the M-Audio. That does add some latency, but it should be within the range REW will tolerate.

To get an idea whether the measurement has given sensible results try looking at the Scope tab. That shows you the sweep REW generated and the signal that was captured via the mic. Not sure how you can get both clipping warnings and a low level warning, they should be mutually exclusive, but the Scope plot may shed some light. Go to the post padding thread to get your post count over 5, wait an hour and you can post a screenshot.
 

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Discussion Starter #5
The Airfoil broadcast directly to the Airport Express nothing actually goes Out through the M- Audio, I think?
I will do some more pad posts and post graphs tomorrow. Thank you for your help!
 

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Discussion Starter #6
Here is a screen grab selection. Sound in room is plenty loud and ECM is showing that it is working. I think that I might not have a closed loop as I am not using the M-Audio out? Screen shot 2010-08-23 at 6.19.41 PM.png

Screen shot 2010-08-23 at 6.55.10 PM.png

Screen shot 2010-08-23 at 6.13.03 PM.png

Screen shot 2010-08-23 at 6.18.28 PM.png

Screen shot 2010-08-23 at 6.19.27 PM.png

Screen shot 2010-08-23 at 6.20.23 PM.png

Screen shot 2010-08-23 at 6.09.33 PM.png

Screen shot 2010-08-23 at 6.08.04 PM.png
 

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Uncheck the "use left as reference" box and tell REW you are using the left channel as input (which is where the mic seems to be connected). Turn the mic gain up a bit on the M-Audio and try again.
 
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