Psalm 81:5

New English Translation

⁵He decreed it as a regulation in Joseph,
when he attacked the land of Egypt.^[a]
I heard a voice I did not recognize.^[b]

Psalm 81:5 tn Heb “in his going out against the land of Egypt.” This apparently refers to the general time period of Israel’s exodus from Egypt. The LXX reads, “from Egypt,” in which case “Joseph” (see the preceding line) would be the subject of the verb, “when he [Joseph = Israel] left Egypt.”
Psalm 81:5 tn Heb “a lip I did not know, I heard.” Here the term “lip” probably stands for speech or a voice. Apparently the psalmist speaks here and refers to God’s voice, whose speech is recorded in the following verses.

New English Translation (NET)