What you say is mostly true, but in the case of sound recordings from before 1972, it's actually the opposite. At the time such recordings were made, they were subject to an infinite copyright term! The Music Modernization Act [1] passed in 2018 to put a finite life on those copyrights. As a result, all sound recordings from before 1923 become public domain this January.

[1] https://en.wikipedia.org/wiki/Music_Modernization_Act