What caused broadcasts to have that “vintage” sound in the mid 20th century

Question

Not talking about the static, mainly the voices of people.

Examples:

https://youtu.be/yYAw79386WI?si=SKCkEeHFLn83ixCB (skip to 4:30)

And a final example of a modern recreation

In: Technology

Answer 1

In the UK, many recorded voices for radio, film and television would have ‘received pronunciation’ which was thought to be especially clear and authoritative – which is why it is often associated with the BBC.

You still hear it in places like announcements on the London Underground and with some presenters on Radio 4 and the World Service, but it is dying out.