For printed music, works published prior to 1923 are in the public domain, although newer arrangements or editions may still be protected.
For recorded music, there is no way to be sure; the vast majority of works will be protected until February 15, 2067 at the earliest.
An extensive list of songs in the public domain (in the US) is linked below. It's much harder to find public domain recordings, as the copyrights for sound recordings are especially convoluted.
Yes; in the US, materials published prior to 1923 are in the public domain.
Yes.
The length of time music takes to enter the public domain can vary depending on various factors such as the date of its creation, copyright laws of the country, and any potential copyright extensions. In many countries, music typically enters the public domain 70 years after the death of the composer or author. However, it's important to consult local copyright laws for specific details.
Yes; US works prior to 1923 are in the public domain.
Materials can enter the public domain when copyright term expires, protection is not renewed (renewals are not available for new works), the creator donates the work to the public domain, or the materials are a work of the US Government.
Because notification is not required for protection, and because protection is automatic, it's usually safest to assume materials you encounter are protected until you can prove otherwise. In the US, sheet music printed before 1923 is in the public domain. Sheet music 1923-1963 is protected if it was renewed, and renewal records can be difficult to trace. Sheet music since 1964 is protected. In the US, sound recordings were covered by state law for many years and were not addressed by the federal copyright act until 1976; with the exception of recordings issued between 15 February 1972 and 1 March 1989 without notice and not subsequently renewed (which are in the public domain), they will be protected through 14 February 2067.
Most "traditional" or "folk" music is of sufficient age (pre 1923) to be in the public domain. Bear in mind however, that if the works are without copyright restriction, revisions to lyrics and music can be done at anytime and those are protected. Additionally while the music and lyrics may be unencumbered individual performances may not be.
It depends what country you're in, and what country the work was created in. In the US, works published in 1917 would enter the public domain, except for the fact that they're already there. Works published in 1978 or later by composers who died in 1941 would enter the public domain, except that that's impossible.
No, and it is staunchly protected by its rightsholders, as licensing it brings in about $2 million annually. In the EU, it will enter the public domain in 2017; in the US it will be protected through 2029.
It is protected in France and other countries with a copyright term of life plus 70 years (such as the US), but in the public domain in shorter-term countries such as Canada.
Yes; Robert W. Service's works entered the public domain in Canada (and other countries that acknowledge the "rule of the shorter term") in 2009. Just to be contrary, that particular poem entered the public domain in the US in 2003.