There’s an article in Techdirt today that discusses just how many books would be available in the public domain if copyright had stayed at its original length. It also references a research article that concludes that the optimal term for copyright is 15 years [PDF link].
I’ve argued in the past in favour of a five-year copyright term, but with indefinite renewal for works that are commercially active, and a ‘use it or lose it’ clause to encourage both a more active commercial exploitation and distribution of a wider array of works and a more vibrant and healthy public domain.
Because far from providing ‘protection’, in most cases, blanket copyright is dooming recordings to be lost to history.