Windows audio mixer control

[EBC Andy B]

Can anyone point me to Windows API docs regarding control of the Windows Mixer? Specifically, I need my code to increase and decrease the volume and turn the input-to-output loopback on and off. I've read a bit on the API but I can't find the specifics on these functions.
Thanks in advance for the fantastic solutions I'm about to receive,
Andy B

 

[Solaris17]

Looks like its under core audio. Here it is for master volume. min 0.0 max 1.0 (100%)

ISimpleAudioVolume::GetMasterVolume (audioclient.h) - Win32 apps

The GetMasterVolume method retrieves the client volume level for the audio session.

docs.microsoft.com