For kicks, I measured my RME ADI-2 DAC FS at different volume gains. As my QA403 does not do USB/digital output, I ran it through a Motu Ultralite mk5 and routed the right channel to Main 2 and SPDIF 2. I fed Main 2 back to the QA403 (left) and the SPDIF to the RME, then the RME right channel to the QA403 (right). Everything is single-ended. The QA403 used a 48 kHz sample, and the Motu was using 96 kHz ADC.
View attachment 256766
The RME is set to Auto Level, so it begins at +13 dBu, then clicks down to -5 dBu at lower volumes. I measured volume at every 6 dB, from +6 dBr to -42 dBr.
These measurements are likely limited by the Motu ADC which I measured at -82 dB THD+N. But they do show how much affect the RME's volume control has it's DAC output.
The +6dB volume setting reads as +2.63 dBV and actually has slightly better THD+N than the Motu DAC. At +0 dB volume (reads as -3.37 dBV), it down 0.04 dB THD+N (or 0.00003%). Here is a table that summarizes them all. The table is only for the right channel, which is the RME output. The first 18 dB stays pretty flat with respect to THD+N because the auto reference level. The volume knob seems pretty accurate too.
Once the Auto Reference has dropped down to the lowest level of -5 dBu, the RME's noise floor is < 110 dB and it barely changes with volume.
|Volume (dBr)||RMS (dBV)||THD (dB)||THD+N (%)||THD+N (dB)|