When ARC is set to download music in ‘CD Quality,’ it downloads music in non-Redbook resolution and not one that makes sense to me.
Consider the following: a high resolution album in my Roon library, say FLAC 96/24, is downloaded to ARC as 48/16. In this case, ARC is running on a current generation iPhone Pro. Now, the 48MHz makes sense as the iPhone DAC does 48 natively and if it was downloaded as 44 I presume the phone would have to upsample to 48 before playback – bad for battery etc. But why does Roon change the bit depth from 24 to 16? iPhone native DAC is 48/24. Reducing bit depth would seem to make no sense.
I know I can download the original resolution, but many of my files are 192/24 and therefore large and more than the iPhone really needs. But “CD Quality” in 24 bit would be nice if the source file is already 24 bit. Even better would be the option to set the specific resolution and bit depth for downloaded files explicitly rather than “CD Quality” or Original as the only options.
I don’t know if this is indeed how ARC was designed, but as far as I can tell, ‘CD quality’ means strictly 16-bit and 44.1 kHz (not MHz btw). Now, if there are 96 kHz tracks, if you want to maintain a power-of-two sample rate ratio, you can down-sample them to 48 kHz instead of 44.1 and still loosely call it ‘CD quality’, as it only increases the size by less than 9%. Bit depth however doesn’t have a power-of-two scheme, so always reducing it from 24 to 16 makes sense if CD quality is the target; if you used 24 bits instead, it would increase the size by as much as 50%, which would beat the purpose of limiting quality.
Not sure if this has anything to do with what the iPhone DAC supports. If you have 88.2 kHz tracks (or other multiple of 44.1), you could check how those are handled.
I understand it’s about choice to do as one desires, but Roon’s strong convictions have always kept that on a short leash.
That said, I wonder if having the theoretical 144 dB instead of 96 dB of dynamic range on a mobile device makes any audible difference, if on any device at all.
You’d probably be hard pressed to distinguish it from 320 kbit mp3.