This expression stands for the ability that God gave John to see into heaven, at least by means of a vision. (See: [[rc://en/ta/man/translate/figs-metaphor]])
How the voice was like a trumpet can be stated clearly. AT: "speaking to me loudly like the sound of a trumpet" (See: [[rc://en/ta/man/translate/figs-simile]])
This refers to an instrument for producing music or for calling people to gather together for an announcement or meeting. See how you translated this in [Revelation 1:10](../01/10.md).