Dictation will not use external microphone
Dictation works fine for me speaking directly into the internal microphone but I cannot seem to get it to work with any external microphone whatsoever. These mics work fine for other applications, and when selected from Preferences > Keyboard > Dictation the little microphone icon on that page does monitor the external mic correctly. However, when I hit the keyboard shortcut to actually use dictation it will always use the internal mic regardless of what mic I have selected. Since I typically work with my mac in clamshell mode this means it's completely non-functional.
Any help troubleshooting this?
MacBook Pro 16″, macOS 10.15