This is a question about metal in general especially children of bodom. I know they use a combination of Harmonic minor keys and major keys. A variety of them. My question is when they switch to a different key is it related or do they switch to completely different keys that aren't related. By related I am talking about the circle of fifths (how many sharps or flats a key has). For example can they change to unrelated keys like from C to G.

I know laiho likes to use P5 changes, move up a major 2nd, as well as down to minor 6ths for some of his changes. And in reply to your "For example can they change to unrelated keys like from C to G." It wouldn't be unrelated, C to G is a P5, which is in every major/minor mode, except the locrian. I guess you can say a change to any key is always somewhat in relation to the original change, you can always relate it to where you came from, that's what modes are for to stay in relation to what key your in, but play alien to the keys scale or root mode. Heh, I think of key changes like a rollercoaster, you start here, you go up some, down some, twist here, turn there, but you always return to where you started. Heh, yea, pretty retarded, and not always the case. Hope this helps....

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you can do anything you want in music, just because it goes againts some theory doesnt meen it will sound band. thats the great thing once you learn theory you can go againts it

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From what I know of Laiho he tends to just use one minor scale during most of his solos for example Cocked and Loaded he just did a bunch E Aeolian(natural minor). No changes, and this is from his tabbed version.

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Each chord is a member of a chordal scale, plus you can switch between the melodic/harmonic chordal scales which will give endless possibilities. There are substitutions for chords to add to the numbers.

99% of the time there is some connection, if one can find it anyway, haha.

Oops I explained my self wrong by giving a totally wrong example! C and G major keys are very closely related. C has no sharps or flats and G has only one sharp with no flats. My question is; is it common in metal that some songs for example switch directly from C to F#/Gb because they are extremely unrelated and switching to those unrelated keys would make it very noticeable. C has no sharps or flats and F#/Gb has 6 sharps and 6 flats making them the most unrelated keys in the circle of fifths.

I do switch keys when I'm arranging but progressively to other related keys which sound good for me. For example C major and A minor have the same notes except they start at different positions which means their modes are different. So when I'm arranging I play modes in C major than start playing A minor modes. To make it a little interesting I sometimes switch from C major key(A minor) to F major(D minor) or G major(minor) key modes since they are closely related by one added sharp or flat. So basically I switch progressively to other keys. I tried changing a couple of times to keys that are extremely unrelated and it sounded bad for me. I'm wondering if they do that in metal. If they do how do they make it sound not so obvious and make it flow coherently!

Schizoid, you hit the nail on the head and this relationship is the same for all the groups on the circle of fifths. The difference between each of the Dominant, Subdominant and Tonic chords is that each of their keys is off by only one note. So, it is very colorfull to play this way...

Manx