Originally Posted by RichB
1'st let me say I am not calling into question your observations.
I have also found differences when playing back different methods.
Did you level match the two, they should be the same but it is a complex path out of a computer?
Note also: the 105D USB DAC bypasses all Oppo processing so that can also produce a difference.
I do not use Audirvana, but on the PC, I have found that subtle changes can be made in the sound quality selecting different driver options, bit-rates, and bit-depths.
Good question, yes, I've level-matched my asynch USB dac with the rest of the OPPOs playback, or rather, i know what levels are equivalent. I describe this a bit below.
USB flash stick and external USB hard drive are both on the standard USB inputs, and should be performing at the same volume levels. After all, the only change in the signal path is at the source device. I've also alternated USB inputs around, and the same results hold true. My flash drive sounds noticeably better than my external (self-powered) hard drive. When my flacs play back off the flash drive, the bass is deeper and more resonant, the highs are crisper. It just doesn't sound as good coming off the external spinner.
Comparing the flash drive with asynch USB, asynch playback via Audirvana wins hands down. By comparison, playback through USB flash sounds muffled.
If I want to dig a little deeper, I can also tell you that moving that same flash drive directly to my Macbook, and having Audirvana play directly off of it, sounds pretty good--better than using the flash to playback through the OPPOs standard USB inputs, as described above. But I get improved sound when playing the files directly off my Macbook's internal SSD drive, vs. having the Macbook read off the flash drive.
So, in order of sound improvement, going from least to best:
1) External USB HD, plugged into the 105D.
2) USB flash drive, plugged into the 105D.
3) USB flash drive, plugged into laptop, playing over asynch. USB, via Audirvana.
4) Internal SSD drive on Macbook, playing over asynch. USB, via Audirvana.
I've compared volume levels with a dB meter, using OPPOs internally generated test tones, throughout. I use 75 dB as the target for my levels. For general use with the OPPO, when I am setting trims and distances, I trim my speakers so that 90% on the OPPO volume control equals 75 dB in all channels. My rear speakers run on their own integrated amp, so I use that to trim the surround volume levels. Then, because I'm running my fronts directly into the OPPO and using it as a preamp, I have to drop my mains a fair bit to get the volume down where I want it. I think both mains are set to -6.5 dB, currently. So, with that -6.5 dB offset, my mains are reading 75 dB at 90%. When I bring those levels up to 0.0, I get the same 75 dB reading at 77%, which is exactly what one would expect: double 6.5 dB (because each percent increment = 0.5 dB), produces a 13% delta.
I typically listen to two channel music at around 73 dB, and thus when listening to FLACs via standard USB, set my volume to 86%, and when listening via Audirvana/laptop/asynch USB, I set my volume to 73%, both of which are equivalent for the OPPO, given my trim levels.