^5:11 And I looked, and I heard the voice of many angels around the throne and the living creatures and the elders; and the number of them was myriads of myriads, and thousands of thousands,

And I looked, and I heard the VOICE of many angels around the THRONE

It almost looks as if there is one voice in which angels sing. Perhaps we would call it "singing in unison".

and the LIVING CREATURES

God's special angels participate too.

and the ELDERS,

We, the redeemed, are represented there too (as a royal priesthood).

and the number of them was myriads of myriads, and thousands of thousands,

The number is beyond our ability to count. This myriads is the same as the one in Hebrews 12:22-23 describing the same gathering at Mount Zion. The way Daniel saw it is described in Daniel 7:9-10. Here not singing but attending as "priests". The court sat ....

Furthermore, from the next verse, this VOICE is not sung at all, BUT is a verbal confession. See also Romans 14:10-12 and Philippians 2:9-11.