This site provides definitions and examples of music textures including monophonic, polyphonic, and mixed versions. (
www.uwosh.edu/faculty_staff/liske/musicalelements/textureframes.html
)
This site offers a general description of musical keys with links to each musical term for further understanding. Please note that users can edit Wikipedia entries, which may or may not introduce errors. (
http://en.wikipedia.org/wiki/key_%28music%29
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This informative link discusses musical form and offers detailed examples with ample text discussion and listening. (
http://www.empire.k12.ca.us/capistrano/Mike/capmusic/music_room/themusic.htm
)
This is another site offering musical examples and definition of texture with listening options for study. (
http://learn.midsouthcc.edu/LearningObjects/Music_Appreciation/musicaltexture/Musical_Tex...
)