I would to know how is key change meaning in music,many of my favourite players do it,for instance the whole song in am and the solo in bm.
what is the effect this produce in the song.It seems to be quite useless for me
but works!!
This should really go in Musician Talk. Try asking there; you'll get better answers.
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Quote by Master Foo
“A man who mistakes secrets for knowledge is like a man who, seeking light, hugs a candle so closely that he smothers it and burns his hand.”

Can you just not apply it to your songwriting or do you not get why it works when others use it? Please clarify your question and I'll address it this evening if it hasn't been addressed in full before then; I have to go to class, and sprint at that!
Well, if you're familliar with how keys work, it's pretty much a just that. A Key change.
Let's say the song is in A minor.
A minor natural scale: A B C D E F G A
If you want to change keys, the best way is to use common tones/chords. Look up the lesson on "modulation" for that.
Let's say you want to change to D minor.
Your D minor scale is D E F G A Bb C D. Now, you're simply not only using this majority of notes, but also resolving to D minor rather than A minor.
This happens in music more often than you think. Sometimes it's done so subtly that you don't notice it, but people with a well-trained ear will probably still hear it.
I can help make each section sound unique. For example alot of popular rock tunes may have the intro in E minor, then move to A minor for the verse, then back to E for the chorus, or maybe up to D. Or maybe C! Music is you're oyster.

Also, it can make thigns a little more interesting for the musician themselves, rather than just playing the same notes throughout a song.
Have you guy's read anything about Joe Satriani's Pitch Axis Theory?