Link to archive.org - 14,500 audio files with 24-bit encoding:
http://www.archive.org/search.php?query=%2...20OR%2024bit%29 (http://www.archive.org/search.php?query=%28format%3A%2824Bit%20FLAC%29%20OR%20%28flac24%29%20OR%20%2824-bit%29%20OR%2024bit%29)
this can be used as source for samples anyone can use, it can be useful to analyze results of tests
nobody will have any problems with copyright, and anyone can share listening test experience
A lot of the search results mention AGP, which is someone's project of ripping obscure vinyl-only releases by musicians in various "avant garde" genres. One of the very first search results is for an AGP rip of a 1969 record on the Columbia label. I strongly doubt that Sony (owner of Columbia) has deliberately released anything whatsoever in their catalog into the public domain or given it a Creative Commons license. Same goes for Nonesuch (under Warner), the label for a record linked to from the AGP info page (http://www.archive.org/details/iaagp), which also happens to mention that they've had some deletions of commercial releases.
So...I would avoid those AGP releases, and I wouldn't blindly assume that everything in the Internet Archive's Community Audio section is necessarily licensed for noncommercial use or is even supposed to be there at all.