I understand how Exclusive Mode would be considered the best bet for optimal fidelity. However, since Exclusive Mode overrides OS controls for an external DAC, I don’t have an ability to select the bit depth and sample rate in the audio setup on osx and thus can’t tell my DAC to upsample, say, something that is 16/44.1 to 24/96. I assume higher-end DAC’s might have upsampling controls on the device themselves, but not so for my JDS Labs ODAC and Merdian Explorer.
Avoiding a debate on whether or not upsampling produces any discernable quality difference aside for a moment, I guess I’m wondering if defining Exclusive Mode as the superior mode for high-fidelity was a “for most setups this will be true” kind of thing, or if there’s something I’m missing that happens to the signal chain if I go through the OS Mixer rather than CoreAudio Direct.
Upsampling can be a great thing for quality under the right conditions.
If I were in your shoes, I’d use exclusive mode. I think it will sound better, even for your setup.
Here’s why:
One issue with the example you posed is: converting between sample rates that are not in the same family (44100/88200/176400 is one family, 48000/96000/192000 is another–rates within the same family are integer multiples of the same base rate, either 44100 or 48000) is an inherently lower quality operation, just due to the mathematical realities of how the algorithms are built. This is why virtually all products that incorporate upsampling as quality enhancement only provide that feature for certain integer multiples–x2, x4, x8.
Another: when you change that setting, you’re telling the Mac to send audio to your device at a given sample rate. This uses CoreAudio’s sample-rate-conversion implementation, which is not known for great sound quality. This setting does not (to the best of our knowledge) trigger high-quality sample rate conversion in your hardware.
As an aside, we are currently in talks with a DSP vendor to license up-samplers for quality enhancement that provide very high quality x2, x4, and x8 sample rate multipliers. Once that’s available, I’d expect it to provide sound quality benefits for your setup.