I’m using a 2009 Mac Pro to run Cubase 8.5.30. Generally, it works fantastically well, to say the least! For the purpose of setting up a separate chain for stereo mixing, I’m using it’s Toslink lightpipe digital connectors as part of an aggregate audio interface, along with a MOTU 2408 mk3 (PCIe-434) connected to a pair of Tascam DM-24 digital mixing consoles. Digital audio is sent from the DM-24 main stereo output, which is set for 24 bit word length (usually at 48k sample rate, clocked to the PCIe-434) to the Mac Pro Toslink input. Core Audio I have set for 24 bit input and output at these (and all) connectors. It is important to note that these settings remain unchanged for any audio application I use, except for Cubase. However, as soon as Cubase is booted, and before a project is even loaded, these settings change to 16 bit in the Core Audio app, and if I try to change it back to 24 bit while Cubase is loaded it will immediately reject it and return to 16 bit. I always have Cubase Project settings set for 24 bit, so when audio is recorded on a Cubase track set for input from the Mac Pro Toslink connection, the files display as 24 bit in the Pool. The sound quality is superb and I cannot tell any difference from the sound coming from my mixing board (which would be from the MOTU 2408 mk3, for certain at 24 bit). Nevertheless, I am concerned about whether Cubase is preventing me from actually achieving full 24 bit resolution. Any idea what’s going on?
I decided to investigate further by doing a simple experiment, and include steps to reproduce (shown below). I unplugged the toslink cables from my Mac Pro, thus assuring that nothing was connected to the Mac Pro’s digital inputs, and therefore assuring that no incoming digital signal could thereby influence Cubase behavior. Nevertheless, this phenomena persisted as outlined in the initial post:
Step #1: In the Core Audio app, set up an Aggregate audio interface, which includes the “Built in Digital Input” and “Built in Digital Output”
Step #2: In the Core Audio app, set the Mac Pro’s digital inputs and outputs to a 24 bit word length. Note that these settings remain intact, regardless of which apps other than Cubase are accessing the built in digital connections.
Step #3: Launch Cubase (It matters not whether a Project is loaded or not). In the Devices window in Cubase, if not already set, the ASIO Audio Driver in the “VST Audio System” should be set to an Aggregate audio interface (it doesn’t matter what the combo is, so long as it includes the built in digital inputs and outputs).
Step #4: Launch Core Audio with Cubase active and check digital input and output settings
Step #5: Note that these settings in Core Audio have changed to 16 bit.
Step #6: Attempt to change same settings to 24bit. Note that it is no longer possible; Settings immediately revert to 16 bit!
Step #7: With nothing connected to the toslink connectors on the Mac Pro, one thing is different: Despite the Aggregate Audio interface synced to 48k sample rate, the digital input reverts to 44.1k sample rate and cannot be changed to 48k sample rate (when the toslink connectors are connected to my Tascam DM-24 mixer, the sample rate matches the system at 48k and stays there, thankfully!)
If this is not a BUG IN CUBASE, I cannot imagine what else could possibly causing this!