I’ve done some digging in this area last year when I wanted some samples or to help with production.
I found that sample sources (original tracks) become public domain or royalty free after 70 years from the IP’s (Intellectual Property) original publishing/recording date. This time bracket also gets hazy because alot of old record companies and publishing houses go through changeovers and get purchased/consolidated with newer umbrella companies – with that, oftentimes IPs get republished under their new ownership/publishing agreements and the 70-year bracket restarts – HOWEVER – if you somehow find a recording of an IP that would be dated outside of 70 years you will find yourself in a gray spot of sorts where you’d be legally free to use portions of the IP.
There are a few places that archive these IPs and make then accessible for royalty free use (with parameters in place for proper credit and creative commons licensing).
In regards to public speeches and news broadcasts I can’t remember exactly what the parameters are but I do know that there are a bulk of items, especially from the Library of Congress and Project Gutenberg that are made available with varied licensing applications.
For further reading and fact finding on purely royalty free sample hunting, check out –
http://www.publicdomainsherpa.com/copyright-public-domain.html (Check out the contents menu on the right)
https://musopen.org/music/
https://archive.org/details/audio
.
