Literature

[Altus]

Choral Public Domain Library
http://www.cpdl.org/wiki/index.php/Main_Page

Werner Icking Music Archive

http://icking-music-archive.org/

Acadia Early Music Archive

http://ace.acadiau.ca/score/archive/ftp.htm

MusiXteX (scores of interest are by Dunstable, Tallis, Byrd)

http://www.mab.jpn.org/musictex/index_en.html#scores

http://www.mab.jpn.org/musictex/chorus_idx_e.html

Laymusic

http://www.laymusic.org/music-publish.html

Mutopia

http://www.mutopiaproject.org/cgibin/make-table.cgi?Instrument=Voice

Cipoo.net

http://www.cipoo.net/music_a.html

Gallery Music

http://www.psalmody.co.uk/contents/music.html