; there's always my job and three kids keeping me busy; etc... Sorry. 
Generally speaking, we define passacaglia as a composition built on a repeating bass melody. The reason we define it this way is that that's what Bach called this piece. Over the centuries, different composers used the word to describe different types of music. But, because of Bach's stature in our eyes (ears?), we do what he said.
Tracks 10 and 11 of this disc are my favorite recording of Bach's Passacaglia and Fugue in C minor:
www.amazon.com/gp/product/B000002ZO1/qi ... c&v=glance
It wouldn't be a surprise if everybody recognizes it. It's been recorded hundreds of times, for organ as well as orchestral transcriptions. It's also heard in many movies and tv shows. The opening scene of White Knights is a good example. If you listen to this excerpt, you hear the theme almost three complete times. First, all by itself. A very sombre melody, eh? It is followed by twenty variations. If you listen for it, you will always hear the theme. It sometimes goes up to the higher notes, sometimes changes rhythmically, but it's always there. In one variation, it's even moved to the foot pedals, while the hands play a different rhythm.
I bumped Foul's Art of Fugue thread, so, if you need, you can read my very short description/definition of what a fugue is. After twenty variations in the passacaglia, Bach uses the theme as a fugue subject. Bach was the Fugue King. I swear, if you dropped a plate on the floor, he'd be able to make a fugue out of the sounds. He was a nut!
Emotionally, this piece takes me all over the place. To me, the theme is sombre. But what Bach does around it is... How can I say it? It's happy, sad, dancing, laughing, crying... Everything! Nobody has ever known how to write variations like Bach. Every musical device can be found, every affect can be felt.
Next, you can move on to Bach's chaconne for unaccompanied violin. Rather than a repeated melodic pattern, a chaconne is a repeating harmonic pattern. Again, this is our definition because that's what Bach called that piece. The Goldberg Variations is probably after that. It's about 80 minutes all by itself!
A girl I used to work with used to bring this in every year and play it for us at Halloween. 
So I was familiar with the work, I just did not know what it was called. 
Especially the first song; I cannot swear to it, but it seems that I have heard this in movies? Maybe old black & white horror movies? 
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