Community Audio (formerly Open Source Audio) is a subset of the Internet Archive Audio Archive specifically for music and spoken word audio files available under one or another of the CC licenses.
The Free Music Archive is a creation of the WFMU radio station in partnership other "curators" and provides legal music downloads in mp3 format from a variety of genres under a variety of pre-cleared rights arrangements.
Metamath Music Page: mathematical proofs set to music! All but one (noted) audio file was placed in the public domain.
Musopen provides public domain (largely classical) recordings and sheet music without any copyright restrictions.
Project Gutenberg , while focusing on texts, does offer a growing number of music digital audio files, sheet music, and audio books under their "Browse by Special Category" search.
The Miller Nichols Library also maintains subscriptions to several streaming media services, which cover permissions for streaming music or film for classroom purposes.
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