I was listening to some CDs through the RME and once in a while I heard some distortion that sounded like my midrange driver was blown. It sounded like a vinyl cartridge mistracking during loud passages. Changed out the dac and the problem went away. I was very confused and began imagining a bunch of ridiculous explanations. I contacted RME, and they asked me to record the output and send the original music file.
Well, it turns out that the problem was major user error due to ignorance. I can see that the RME is clearly intended for studio use or for more sophisticated users. By selling to the consumer market I am sure that their support team gets a lot of questions that have them just shaking their heads
Between their complex user interface and general lack of knowledge on the part of us consumers... whew. For one thing, I don't understand how digital volume control works...
In any case, I resolved the problem before I had any further communications with them (it is the weekend). Below is the email that I sent to them telling them that I had resolved the problem. It may be useful to anyone else who messes things up like I did. I asked a few question just for my edification. So if anyone here wants to lend their expertise and provide some answers, that would be welcome.
My setup is RME (RCA outputs) -> passive preamp (volume control and switching only) -> amplifier
"I am overloading the output! I didn't realize that this kind of thing was possible. I assumed that the DAC would not permit "clipping" (if that is the right term?) at the output. I had set the reference level and turned the volume up to its maximum, +6db! It finally occurred to me that the red and yellow that were being displayed on the level meters was analogous to the levels on tape recorders and ADAT machines, where in the case of tape recorders it indicates tape saturation. So I just reduced the DAC volume and the distortion went away. It also explains why I could hear the distortion on some CDs and not others. Some CDs are recorded at higher levels than others. Watching the level meters made this very clear. Could you explain what is going on when I see red and yellow and hear distortion? I would like to know so that I have a clearer understanding. Also could you explain what is going on when I increase the reference level? The reason I ask is that the if I set the volume so that there is no distortion and then increase the reference level, their is still no distortion even though the volume increases with the reference level.
What is the best way to ensure that I get the widest dynamic range using the DAC volume reference level and DAC volume control? There is some kind of "auto" feature, but I am not sure what it does. Remember that I am running the DAC into a passive preamp from which I can control the volume. At the moment I set the dac volume to the highest it can be set without the level meters turning red. Then I adjust the preamp volume."