Okay, if no one knows the answers for sure, then I could use a little help finding tools or techniques to get the answer to my second question in particular.
What software or hardware tools could I use to measure or view the output sample rate from the tablet that is going to the DAC? I’ll contact Oppo to see if they have any way to provide the user with the source sample rate that the DAC is getting. Meanwhile, does anyone have any other ideas?
As far as I know, Android samples all audio at 44.1khz using 16bits per sample. To get around thing you need an OTG cable and to run a software like USB Audio Player Pro which includes USB drivers that by passses Android’s internal.
Thank you. I have a trial of that software and it seems to work as you describe. I just wish there was a way to send Roon’s output to UAPP, or better yet, to let Roon use UAPP’s USB driver. I got the tablet just for Roon, so UAPP has limited appeal. (I use iAudioGate on my iPhone to listen to local hi-res audio files using my Oppo DAC.)
I got hold of a FiiO Alpen 2 (E17K USB DAC) that has a display readout of the sample rate and bit depth of its input source – sort of. It groups all hi-res sample rates above 48k in a 96kHz/24-bit readout, and all sample rates 48k and below in 48kHz/16-bit readout. Actual bit depth is irrelevant to the displayed SR/BD. This is a case of “some is better than none”.
So I tried it with a Samsung S7 Edge and my cheap Insignia Android tablet.
S7: Using built-in players and the Google Play app, the S7 always sent a hi-res signal to the DAC. The display never varied from 96/24 no matter what the file type, sample rate or bit depth of the source was. So I take that as confirmation that the S7 always upsamples output to match the highest sample rate of the connected DAC. I could get proper sample rate output to the DAC by using the USB Audio Player Pro and its proprietary USB driver (as expected).
Tablet: Roon Remote on the tablet could only send a max of 16/48 audio to the DAC. Any attempt to play hi-res files from Roon resulted in a “Transport: playback_error_endpoint_device_init_failed” error message. But the good news is that when I did play back 16/44.1 CD quality tracks from Roon, the DAC didn’t indicate any upsampling at all. The display read 48kHz/16-bit, unlike the S7.
So in my case at least, I’m fairly certain I can take my tablet on the road with me, connect to Roon via my VPN, hook up my good Oppo DAC to the tablet, and be able to play back CD-quality audio from my home music library without any unwanted upsampling going on. That was the goal of this whole experiment anyway.
EDIT: Porcupine Tree’s “Fear of a Blank Planet” at 24/48 also plays properly from Roon on the tablet once the audio endpoint settings in Roon are set to “Up To 48k” and “24-bit” So even better than I thought!
Interesting. If multiples of 48k are allowed, then I’d like to find out why Roon choked on my 24/96 files when I tried to play them back on the tablet. The error message seems to indicate that something external to Roon was telling Roon, “you can’t do that”.
Didn’t Android 5.0 allow 44.1 kHz audio to be sent to attached USB devices?
I think, irregardless which version of Android used, the OS will always sample rate to 48k multiple. The only way is the app must design to bypass the SRC(Sampling Rate Conversion) in the OS. The app itself will show the bit/sampling frequency. One example is FiiO X7 portable android audio player. If Roon will ever build a native app for android OS, that will be great, can enjoy high quality music on the go!