R. Kelly may be behind bars … but he proved his vocal chords are as free as ever during a rare podcast interview when he serenaded the audience by singing two snippets of his songs.

The disgraced rapper — who is currently serving a 30-year sentence for federal racketeering and sex trafficking convictions — appeared on the “Inmate Tea with A&P” podcast and performed part of his 1998 song “When a Woman’s Fed Up” and later, some of his 2003 track, “Step in the Name of Love.”

Kelly confirmed his conviction hasn’t diminished his love for music, explaining … “Singing is a beautiful disease that’s uncurable … I’m always singing.”

Though he seems plenty busy behind bars in federal prison in North Carolina, he said he’s “working on getting out” so he can fully get back to his craft … adding that he is “using patience as a tactic.”

As you know … in addition to his federal conviction, RK was sentenced to 20 years in Chicago for his federal sex crimes case.

A federal judge sentenced him to just one additional year in prison … with the other 19 years being served concurrent with his original sentence.

However, a federal appeals court upheld his racketeering convictions and a 30-year prison sentence in February … so it looks like he will have time to write another 25 albums.