Timothy A. Smith has created an amazing site on Bach, full of analyses on canons, fugues, the Well-Tempered Clavier, Goldberg variations, and more. Here is a snippet from information on the canons of the Goldberg variations: - - - - - - Canon 1: canone all' Unisuono Structurally, the Goldberg Variations demonstrate the Baroque ideal of balance and internal coherence. Every third variation is a canon, of which this is the first. Canone all' Unisuono means "canon at the unison," implying that the canon leader
and follower begin on the same pitch. This title suggests that subsequent canons might use other intervals as indeed they do.
- - - - - - A lot of pages on the site feature Flash and Shockwave work that play musical bits from pieces to help illustrate certain points. Highly informative. Here is the main site on Bach.