Making piano software

[Gostoso]

Hi everybody, I am developing sight reading software for the piano/keyboard and I have a question about it. My software generates single notes, intervals and chords for the left and the right hand, BUT it is possible that those notes don't sound NICE together at all. Is there a rule (theory) that explains the harmony between chords and intervals. So would a Major G chord in the right hand sound well with a for example Major F chord in the left hand? Why? or Why not?
Hope anyone can explain it to me well enough so I can translate into programming code   Thanks!

[davy10tunes]

Gostoso

There are rules about harmony.You want your notes to form a consonant (nice) harmony, rather than a dissonant harmony.An F major chord will not sound good with a G major chord because it is not part of the G major scale.To find out what all the chords are in a certain key, you need to build a triad on every note of the scale.I'll give you an example using the G major scale:
There are 7 notes in the scale, G to Fsharp, a chord can be built on each of these notes and they are numbered 1 to 7(in harmony roman numerals are used)
chord No.                      I   II   III   IV   V   VI   VII
notes of the scale:       G   A    B     C   D   E     F sharp(*)

now we make triads:    B  C    D     E   F*  G     A
to reveal the chords     D  E    F*    G   A    B    C
of the particular key
So now we know what chords belong to G major.
Chord I G maj, II a minor, III B maj etc.
However, this does not mean that because 2 chords belong to the same key, they can be played simultaneously.(you can use the above rule to make chord progressions ) If you want bitonal harmony like ravel for example, you can combine some chords of 2 scales a 3rd apart, for example C major and E flat major/minor, but It's been so long that I studied this stuff, I can't remember the rules, the best thing I can suggest is to read a book on harmony, which will explain it a lot better than I can.

David  

[davy10tunes]

Sorry the chord numbers and notes didn't line up.They did when I wrote it but moved when I posted it, but you can still understand it I hope. :-/

David

[Gostoso]

Hi David, thanks for your reply, but unfortunately I have a book in front of my which tells me already that I is associated with a Major chord, II with a Minor, III with a Minor, IV with a Major, V with a Major, VI with a Minor and VII with a Diminished Chord. My program already generates chords that 'belong' to a certain key, I find it really cool.. But unfortunately the harmony is sometimes nowhere to be found, so that is definitely the main problem. I will try to find some more information on harmony, but thanks anyway.