On the Mac, most people who run software have now upgraded to Mojave 10.14 (if not yet Catalina, 10.15). The engineers at Metric Halo (MH) make excellent audio interfaces and write generally good/stable mac drivers. In their current interfaces, they have implemented audio over ethernet (as well as USB C) with their own driver. MH devices with their Mac software driver doing audio over ethernet worked with REW 5.19 on the last release of High Sierra (10.13.6). However, 5.20 beta versions of REW (at least starting in 2018) did not work on the same machine running 10.13.6 with the same MH hardware/software, i.e., when selecting to test levels from the preferences menu in REW 5.20, audio is seen being generated on the REW level meter, but audio no longer shows up in the MH software mixer window (as it did with REW 5.19).
Similarly, on Mojave's last release (10.14.6), the latest beta version of REW 5.20 has the same issue. The current version of REW 5.20 also displays a notification that the microphone cannot be accessed on the machine even though the audio input in REW is set to be the MH audio interface. Giving REW permission in the Mac system preferences to access the microphone does not prevent getting this notification. I have tried making the MH audio interface the default audio device in the Mac system preferences, and then for output selecting the default device (or the default audio device) in REW 5.20 preferences instead of directly selecting the MH driver. But none of these (3) selections in REW for an output device causes audio to show up iin the MH software mixer window with REW displaying output level in test mode. The above makes it seem like REW 5.20 does not see the MH audio interface at all for input or output.
Since REW 5.19 is listed to not run on Mac OS 10.14, then it seems I would need to revert back to running Mac OS 10.13. That would be difficult to do now as we finally had to uprgade from MacOS 10.13 to 10.14 to run current versions of other applications. So happy to learn if there are any workarounds to run some version of REW with MH drivers on Mac OS 10.14.6. I do have access to a machine running Mac OS 10.15 which I could try, but from the above I was not expecting REW 5.20 to work any differently running on 10.15 compared to 10.14.
Similarly, on Mojave's last release (10.14.6), the latest beta version of REW 5.20 has the same issue. The current version of REW 5.20 also displays a notification that the microphone cannot be accessed on the machine even though the audio input in REW is set to be the MH audio interface. Giving REW permission in the Mac system preferences to access the microphone does not prevent getting this notification. I have tried making the MH audio interface the default audio device in the Mac system preferences, and then for output selecting the default device (or the default audio device) in REW 5.20 preferences instead of directly selecting the MH driver. But none of these (3) selections in REW for an output device causes audio to show up iin the MH software mixer window with REW displaying output level in test mode. The above makes it seem like REW 5.20 does not see the MH audio interface at all for input or output.
Since REW 5.19 is listed to not run on Mac OS 10.14, then it seems I would need to revert back to running Mac OS 10.13. That would be difficult to do now as we finally had to uprgade from MacOS 10.13 to 10.14 to run current versions of other applications. So happy to learn if there are any workarounds to run some version of REW with MH drivers on Mac OS 10.14.6. I do have access to a machine running Mac OS 10.15 which I could try, but from the above I was not expecting REW 5.20 to work any differently running on 10.15 compared to 10.14.