A new Discord feature is available now and it allows priority speakers" within voice calls. When the priority speaker talks, the voices of all others will be lowered.
Raid leaders across the world cheer! Give roles the Priority Speaker permission and Discord will lower other peoples' voices when they speak. You'll see a green dot in the voice chat list next to people who have priority. pic.twitter.com/F91YTpYrZJ— Discord (@discordapp) August 2, 2018