This site provides music theory information on such topics as rhythm, intervals, scales, chords, etc. Also, there is a fine section which describes the basic concepts of form and structure.

This site looks at rhythm, terms and concepts, which include rhythm, score, note (parts of and kinds), rests, tie. Great information.

In music, notes often times must be articulated in certain ways. This site explains the various common articulations found in most music.

The author offers a complete explanation of the physics behind piano tuning and why piano tuning is an intricate process. Illustrations and graphs are included.