Still, opinion from my professor:

Any musical works published after 1923, and virtually all commercial sound recordings, are still under copyright in the U.S., and it is a violation of U.S. copyright law to post them online without the permission of the copyright owner. If you want to be safe, do not post or download any music or songs online without permission.

In many other countries, sound recordings receive only 50 years of protection, so sound recordings distributed to the public before 1956 would be in the public domain in those countries. In the U.S., however, sound recordings made before 1972 are governed by state law, not federal
law, and in some states copyright protection for sound recordings is perpetual until preempted by federal law in 2067.