Its a small gist helps to know which apps using microphone ( which are in active state)

go.mod

module microphone

go 1.14

require (
	github.com/go-ole/go-ole v1.2.4
	github.com/moutend/go-wca v0.2.0
)

go.sum

github.com/go-ole/go-ole v1.2.4 h1:nNBDSCOigTSiarFpYE9J/KtEA1IOW4CNeqT9TQDqCxI=
github.com/go-ole/go-ole v1.2.4/go.mod h1:XCwSNxSkXRo4vlyPy93sltvi/qJq0jqQhjqQNIwKuxM=
github.com/moutend/go-wca v0.2.0 h1:AEzY6ltC5zPCldKyMYdyXv3TaLqwxSW1TIradqNqRpU=
github.com/moutend/go-wca v0.2.0/go.mod h1:L/ka++dPvkHYz0UuQ/PIQ3aTuecoXOIM1RSAesh6RYU=

main.go

package main

import (
	"fmt"
	"github.com/go-ole/go-ole"
	"github.com/moutend/go-wca/pkg/wca"
	"log"
	"strconv"
)

func main(){

	if err:= ole.CoInitialize(0); err != nil{
		log.Println("Error in initialize")
		log.Fatalln(err.Error())
	}
	pEnumator := &wca.IMMDeviceEnumerator{}
	pSessionManager := &wca.IAudioSessionManager2{}
	if err := wca.CoCreateInstance(wca.CLSID_MMDeviceEnumerator,0,wca.CLSCTX_ALL,wca.IID_IMMDeviceEnumerator,&pEnumator); err != nil{
		log.Fatalln(err.Error())
	}

	dCol := &wca.IMMDeviceCollection{}
	if err := pEnumator.EnumAudioEndpoints(wca.ECapture,wca.DEVICE_STATE_ACTIVE,&dCol); err != nil{
		log.Fatalln(err.Error())
	}

	var dCount uint32
	if err := dCol.GetCount(&dCount); err != nil{
		log.Fatalln(err.Error())
	}
	var i uint32
	for i = 0; i < dCount; i++{
		pCaptureDevice := &wca.IMMDevice{}
		if err := dCol.Item(i,&pCaptureDevice); err != nil{
			log.Fatalln(err.Error())
		}

		pProps := &wca.IPropertyStore{}
		if err := pCaptureDevice.OpenPropertyStore(wca.STGM_READ,&pProps); err != nil{
			log.Fatalln(err.Error())
		}

		varName := &wca.PROPVARIANT{}
		if err := pProps.GetValue(&wca.PKEY_Device_FriendlyName,varName); err != nil{
			log.Fatalln(err.Error())
		}
		device := varName.String()
		fmt.Println("\n\nMicrophone: "  + device)
		if err := pCaptureDevice.Activate(wca.IID_IAudioSessionManager2,wca.CLSCTX_ALL,0,&pSessionManager); err != nil{
			log.Fatalln(err)
		}

		if pSessionManager == nil{
			log.Fatalln("Not found session manager!")
		}
		cbSessionCount := 0
		pSessionList := &wca.IAudioSessionEnumerator{}
		pSessionControl := &wca.IAudioSessionControl{}
		pSessionControl2 := &wca.IAudioSessionControl2{}

		if err := pSessionManager.GetSessionEnumerator(&pSessionList); err != nil{
			log.Fatalln(err)
		}

		if err := pSessionList.GetCount(&cbSessionCount); err != nil{
			log.Fatalln(err)
		}

		log.Println(fmt.Sprintf("Session Count: %v", cbSessionCount))
		for j := 0; j<cbSessionCount; j++{
			fmt.Println("\n\nSession " + strconv.Itoa(j) + ":-")
			if err := pSessionList.GetSession(j,&pSessionControl); err != nil{
				log.Fatalln(err)
			}

			if err := pSessionControl.PutQueryInterface(wca.IID_IAudioSessionControl2,&pSessionControl2); err != nil{
				log.Fatalln(err)
			}

			instID := ""
			if err := pSessionControl2.GetSessionInstanceIdentifier(&instID); err != nil{
				log.Fatalln(err)
			}

			log.Println(fmt.Sprintf("SessionInstanceIdentifier: %v",instID))

			var state uint32
			if err := pSessionControl.GetState(&state); err != nil{
				log.Fatalln(err)
			}

			switch state {
			case wca.AudioSessionStateActive:
				log.Println("Session state: Active")
				break
			case wca.AudioSessionStateInactive:
				log.Println("Session State: Inactive")
				break
			case wca.AudioSessionStateExpired:
				log.Println("Session State: Expired")
				break
			default:
				log.Println("Session State: Not Found")
			}
		}
	}
}

An example of how it shows