This guide will help in setting up microphone to work trough the RDP connection.
Configuring Device Redirection Services
First step is done on the local PC and target server. Run “gpedit.msc”:
Go by path:
Local Computer Policy -> Computer Configuration -> Administrative templates -> Windows Components -> Remote Desktop Services -> Remote Desktop Session Host -> Devise and Resource Redirection-> Enable “Allow audio recording redirection” и “Allow audio and video payback redirection”:
Enabling Windows Audio Services
Search for “services”: 
Find and open “Windows Audio” Service:
In the “Startup type” choose “Automatic” so that service is always available:
Updating registry settings
Run “REGEDIT”:
Go by path HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Terminal Server\WinStations\RDP-Tcp
Find fDisableAudioCapture and set to 00000000:
Adding role “Remote Desktop Session Host”
In the Start menu look for a “Server Manager”:
Click on the “Manage” and choose “Add roles and features”:
Next you will encounter a series of steps to finish installation. Following action order will tell you what to do on each step:
1)Next
2)Choose Role-based or feature-based installation + Next
3)Next
4)In the list choose “Remote Desktop Services” + Next
5)Next
6)Next
7)Choose Remote Desktop Session Host + Add Features + Next
Now install services and reboot the server.
After that don’t forget to allow the usage of the microphone in your RDP client and everything should be working fine. If you encounter any issues feel free to ask us via ticket or online chat. Thank you for reading!
Source: https://serverspace.io/support/help/how-to-use-microphone-in-rdp-session