Can anyone school me - I am going nuts trying to understand where I am going wrong trying to do what I thought should be a simple test:
 
I want to test my audio interface fidelity by taking an imported ripped wave from a CD and sending it out a stereo pair on my interface while recording it back in through a stereo pair.  The idea is that I'll repeat this 10x or 20x and see what kind of degradation and artifacts I notice when I A/B the first generation and last generation recordings.
 
Here is what I did:
 
1. I ripped a lossless wav file from a CD to serve as my source audio
2. Opened Sonar and dragged the .wav file into a track.
3. Configured the output to ports 3/4 on my interface
4. Wired 3/4 out to 3/4 in
5. Added another track, set it to record from 3/4 in
6. Recorded a second pass from track1 to track2
 
What I expected was that I would see track2 matching track1, at least with respect to levels.  All faders and gain are at unity.  I use a Focusrite Liquid56 and as far as I can tell, gain is unity.
 
What I actually see is that the recorded track is hotter than the source track by a seemingly variable amount.  I've tried changing the volume on my source track1 to -1.0db and -0.5db and while this seems to give me a similar level on my track2, when I play back track2 to repeat the process to track3 for a third generation, the volume is mismatched again.
 
I can't help but think I'm doing something wrong ...  I've been unable to record several generations and have the volume matched, and I don't understand why.
 
Have I overlooked something simple?
 

The Liquid 56 has modeled channels, right? Any chance those are interfering?

There is nothing within Sonar that lets you modify the volume of a signal being recorded.
 
Any perceived change MUST be attributable to something outside Sonar in your recording chain.

im not sure your going to find what your looking for. there really is not any "degradation and artifacts" in digital audio when doing an export, bouncing technique. not like analog was.
if there is, it will be so minute (as in mi-noote) it almost isn't even audible.
 
 
but to complete your test, you need to make sure your tracks, master and Hardware from the liquid is all at unity gain. as in 0dB.
if something doesn't sound right on the export, its because something was not at 0dB.
also, how are you metering ?
as a test try this:
click on the output of the master bus and select "new stereo bus" put a meter in that bus and the master bus.
don't ask why. just test the difference between that buss and the master bus meter.

https://www.youtube.com/watch?v=-8_b1xfOrJY    heres a video I made that deals with examining the outside world with the inside world.. signal levels on your interface preamps etc.

You test is pointless. Setting controls at unity does not mean the signal will not be changed. 
 

Cactus Music
You test is pointless. Setting controls at unity does not mean the signal will not be changed. 
 

The op problem actually suggests that there is in fact a level descrepency when he takes his tracks out of the box and back in.  On many interfaces finding unity gain is not crystal clear, so this trouble shooting technique may help clarify whether its a coloring from the liquid preamp, thats causing the descrepency, or actual voltage.. i.e. if hes using the mic level instead of line etc.

Differences in apparent peak level of only 0.5 to 1.0dB are probably just due to relationship of the sample to the actual analog peak (i.e. inter-sample peaks are higher than the samples on either side). SONAR's meters are just giving a graphical indication of the raw sample levels; it doesn't do a virtual D/A conversion and show you what the actual analog peak is (that would be too CPU-intensive). Because of the way A/D/A conversion works, the analog level will be accurately reproduced even if there's no sample taken at that actual peak level (the analog output isn't simply a curve drawn through the sample points - the conversion process is much more complex than that).
 
In any case, I would not worry about such small discrepancies. Even if real (e.g. your converters perform inconsistently), and not artifacts of looking at raw sample values instead of the resulting analog output level, such small discrepancies in local peak amplitudes is not going to significantly affect what you hear.
 
It occurs to me that another source of variation from one recording of the same source to the next will be the performance of the analog pre-amps and anti-aliasing filters on the inputs. It's doubtful they will behave exactly the same way every time. That's a lot of what your serial re-recording test is going to be measuring.

Cactus Music
You test is pointless. Setting controls at unity does not mean the signal will not be changed. 
 

 
I might not have explained well, but I don't think it is pointless, and it is not about gain, per se.  What I am testing is the artifacts of my AD/DA conversion stages and analog circuitry by running a track out a pair of DACs and back in another pair of inputs though the ADCs, through several generations to enhance the artifacts.
 
Where I am confused is that I cannot seem to easily match levels and I expect if I record something in and it registers at -3.0db that I would get -3.0db on the analog outputs if I set the Sonar track volume to 0.0db and gain at 0.0db and have my interface at 0.0db (unity) as well.  In reality, I seem to be seeing shift, and I'm having a hard time compensating for it so that each generation has the same levels.
 

chuckebaby
im not sure your going to find what your looking for. there really is not any "degradation and artifacts" in digital audio when doing an export, bouncing technique. not like analog was.
if there is, it will be so minute (as in mi-noote) it almost isn't even audible.

Thanks for the response.
 
Any degradation would be from the fidelity of the DACs and ADCs and the analog circuitry around them in my interface - I'm outputting to a pair of analog outs and back in another analog input pair, so I'm testing the converters and analog portions of the interface, not using a digital loopback which would simply make a copy of the bitstream.
 
I will try your buss/metering test - I'm not sure what it implies, but I'll try.