Attempting to transcribe a piano piece and I was planning on using the original tune for reference, however everything other than Dorico is unfortunately muted. I can’t yet figure out how to unmute. Advice appreciated.
It depends on the driver and driver settings.
What OS are you on, what driver resp. audio interface do you use?
Windows 10 x64, using “Realtek High Definition Audio”, version 6.0.1.7535.
Everything on the volume mixer is at 100%, nothing is muted. Testing sound does nothing, visually or aurally.
Edit: If I attempt to play the reference mp3 using VLC, I get:
[02ab29e4] directsound audio output error: cannot start playing buffer: (hr=0x8889000a)
Edit 2: Windows believes the problem is with “Generic Audio Driver”.
Edit 3: I tried testing the audio device in Playback Devices.
Device In Use
The device is being used by another application. Please close any devices that are playing audio to this device and try again.
Doubtless that application is Dorico, but I have no idea why it would preclude other apps from playing audio.
Edit 4+6: Fixed!
In Dorico:
Edit >
Device Setup >
Device Control Panel (ASIO Driver: Generic Low Latency ASIO Driver) >
Uncheck “Allow ASIO host application to take exclusive control of selected port configuration”>
Edit 5: Unfortunately, while unchecking this option frees up other applications to play audio, Dorico will not play anything.
Edit 6: Ignore Edit 5.
Check "User definable under “Audio buffer size”.>
Drag the buffer size up in milliseconds. I went from 10ms to 50ms and now all applications output audio.
Have you tried the Preference option to let Dorico release control of the audio driver when the program loses focus?
I managed to fix it after the saga of edits. 
Hopefully I’ve provided enough information so that other people who have this issue can see what worked and what didn’t in my case.
This also works, and without the workaround