Edited
I don't want to flog this to death.
At unity gain for the Model 24, the only reasons for the signal level discrepancy between Reaper and the mixer is either
- The meter measurement (VU vs dBFS), or
- There's a unity gain or gain staging discrepancy due to something that may be influencing the signal (Trim control, compressor, EQ, fader precision, centered pan knob, etc). If this is the case, something is amiss and requires correction.
At unity gain, at all gain stage points, what goes in should be what comes out.
BUT
That means you do
not have unity gain throughput on the mixer. Until you establish unity gain throughput (that's Zero VU input to output for the 16/24), you can't draw any conclusions about the level of what's being printed to the 2T SD card on tracks 23/24.
See this post in the Model 12/16/24 Tips & Tricks sticky for a discussion of Model 16/24 metering.
Analog VU (dBu) vs Digital dBFS
(From the Model 24 Level Diagram)
Zero dBu (zero VU) analog translates to almost -20 dBFS on the digital SD card.
Click to Enlarge
View attachment 2284
This is why the signal taken from the SD card plays at a lower level on the computer; and why an incoming -20 dBFS signal will be near or at Zero VU on the unit meters if unity gain has been established.
See
this post for additional information.