Dictation not working on clamshell mode with external mic

What you are seeing is the default behavior with the newer T2 chips.

https://www.businessinsider.com/apple-macbook-air-and-2018-macbook-pro-disconnect-microphone-when-lid-is-closed-2018-11

As a workaround (which is not an ideal solution) until Apple changes things, you can enable Voice Control.

1. Choose Apple menu  > System Preferences, then click Accessibility.
2. Click Voice Control in the sidebar. 
3. Enable Voice Control

drsang wrote:

The T2 chip should have nothing to do with it not working with an external USB mic. It works with everything else except dictation.

It might have to do with the specific model of external mic and drivers it may have. What type of external mic are you using? Is the external mic detected and properly identified -- check in About this Mac ...

I'm having the same problem. My 2019 MBA is in clamshell mode when I connect it to an external monitor/keyboard/mouse. All other apps work with my external USB mic except dictation. Apple, please help.

the default behavior of a macbook which is closed is to go into sleep mode to conserve power, the problem is yours rather than a general one

read

https://www.hellotech.com/guide/for/how-to-keep-laptop-on-when-closed

more

https://www.google.com/search?sxsrf=ALeKk03clEO_yTq-a8_QlHTc9nljxAGE7g%3A1599315313084&ei=cZ1TX4jXBMnhkgWngKqoAg&q=mac+don%27t+sleep+when+lid+closed&oq=mac+don%27t+sleep+when+&gs_lcp=CgZwc3ktYWIQAxgAMgUIABDLATIFCAAQywEyBQgAEMsBMgUIABDLATIGCAAQFhAeMgYIABAWEB4yBggAEBYQHjIGCAAQFhAeMgIIADIGCAAQFhAeOgQIIxAnOgQIABAeOgYIABAIEB46BwgAEEYQ-QE6AgguOgYIABAHEB46BAgAEEM6BQgAELEDOggIABCxAxCDAToKCC4QsQMQgwEQQzoECAAQCjoFCC4QsQM6BggjECcQEzoECC4QQzoHCAAQsQMQClCuH1ipxw5gsswOaAFwAHgAgAGIAYgB-w2SAQQxNS41mAEAoAEBqgEHZ3dzLXdpesABAQ&sclient=psy-ab

The T2 chip should have nothing to do with it not working with an external USB mic. It works with everything else except dictation.

I am using a webcam with mic. It works with Siri, Zoom, and just about every other application that requires access to the microphone except dictation.

@Rudgar, Not sure you understood the question. The problem isn't keeping the Mac awake when the clamshell is closed. It's that Dictation doesn't work. Other services such as Zoom, Teams, FaceTime, and Voice Control all work when the clamshell is closed, just not Dictation. This leads me to believe it's a problem with the app, and I'm one of those who would like it fixed.

Maybe it will be addressed in Big Sur.