If you find your Siri or Dictation application that requires voice input through your internal microphone is not working whenever you plug in CalDigit Dock that has external microphone such as Thunderbolt Station 3 or USB-C Dock, this is because Siri or Dictation automatically chooses the input microphone to the external one by default. In CalDigit dock, it could be “USB audio CODEC”. To overwrite this default setting, you can change “Automatic” to “Internal Microphone” from system preference. For example:

Siri
Go to System Preference -> Siri and select the the Dock mic input

Dictation
Go to System Preference -> Keyboard -> Dictation and select the input from the list on the left-hand side

If you want to use CalDigit’s dock as the default voice command input, you can choose “USB audio CODEC” from the setting.

Additional Information:
Use Siri on your Mac
Setting Thunderbolt Station audio ports as default audio input and output