Who are these angels?

Revelation 5:11 (ESV)

11 Then I looked, and I heard around the throne and the living creatures and the elders the voice of many angels, numbering myriads of myriads and thousands of thousands,

These angels are all faithful servants of God who have heard the call of the mighty angel in Revelation 5:2 and seen the Lamb approach the throne to take the scroll from God’s hand. They follow the lead of the inner circle in loud songs of praise for what they have witnessed.