Today I got my UR242, nice piece of ringy hardware (literally it rings when you slide you finger in the front chassis).
I always like to know how many dBFS corresponds to +4dBu in every card that I own and since I’m with heavy insomnia and bad stomach right now. I did some input test using a Behringer CT100 cable tester (that also can send test tones). It becomes handy when you need to put an external PRE (or similar), but well…somehow, I got lost in the way… let’s see…
Parameters
The test was made sending a 440hz tone at +4dBu and other at -50dBv (mic level), using XLR and TRS cables.
The Pre’s gain knob was always set at minimum.
Also a loopback test was made using a stereo Channel with the Test Generator plugin(Cubase 8 PRO) sending also a 440hz tone. This at -12dBFS (here the output knob was at maximum)
Only the Loopback channel was routing to the main output
A little bit less
I find out something quite similar to my UR824, in the inputs with PRE’s, the pair Inputs have always a little bit less gain that the odd one (around -2dB). In the UR242 this will be Input 2.
The Inputs without Pres (3 and 4) are exactly the same.
Here a capture:
How About what +4dBu is…
Doing some Maths.
In Channel 1 a +4dBu was feed with the PAD on, according to the technical specifications, the pad always applies -26dB and has a fixed gain of +12dB (in the specs says “Gain Range +12 dB - +56 dB”) so:
+4dBu-26dB+12dB = -10dBu was the entry signal.
In Cubase, this was -19dBFS
Then
-10dBu = -19dBFS
-10dBu + 14dB = -19dBFS+14dB
+4dBu = -5dBFS
How about with the Pad?
Channel 3 is being feed with a -50dBv Signal, without pad. So first we must pass this to dBu (I will use 4 decimals)
log…antilog…blablabla
-50dBv = -47.7815dBu
applying the fixed gain:
-47.7815 + 12dB = -35.7815dBu is the entry signal.
Here Comes the weird stuff
In Cubase, this was -37.4dBFS
Then
-35.7815dBu = -37.4dBFS
-35.7815dBu + 39.7815dB = -37.4dBFS + 39.7815dB
+4dBu = +2.3815dBFS ???
So, I’m doing something wrong but for god sake, I can’t find what it is… 
