John Gill Commentary Job 30:31

"Therefore is my harp [turned] to mourning, And my pipe into the voice of them that weep." — Job 30:31 (ASV)

My harp also is [turned] to mourning
Which he used, as David, either in religious worship, expressing praise to God thereby, or for his recreation in an innocent way; but now it was laid aside, and, instead of it, nothing was heard from him, or in his house, but the voice of mourning:

and my organ into the voice of them that weep ;
another instrument of music, which had its name from the pleasantness of its sound, and was of early use, being first invented by Jubal, (Genesis 4:21) ; but not that we now so call, which is of late invention: those instruments which Job might have and use, both in a civil and in a religious way, were now, through afflictions, become useless to him, and neglected by him; or these expressions in general may signify, that, instead of mirth and joy he was wont to have, there were nothing now to be heard but lamentation and woe; see (Lamentations 5:15) (Amos 8:10) .