[quote]krome (1/30/2010)[hr]Hi Mike glad you saw the funny side of the link. 
[quote]
My question was more something like “why use one instead of another ?” or “How comes there are three scales for a single note ?” or “Is one of them more appropriate depending of the type of music you are producing ?”[/quote]
To be honest I could write a ver bad book about why use one over another but I suppose the succinct answer is each of the 3 minor scales has its own particular flavour or fingerprint.
Not only for melodies but for the accompanying harmonies too.
C Melodic Minor scale notes: C D Eb F G A B
Cmin Dmin Ebaug Fmaj Gmaj Adim Bdim
C harmonic minor scale notes: C D Eb F G Ab B
Cmin Ddim Ebaug Fmin Gmaj Abmaj Bdim
C natural minor scale notes: C D Eb F G Ab Bb
Cmin Ddim Ebmaj Fmin Gmin Abmaj Bbmaj
I encourage you to try each to get an idea of how they sound.
Also notice all three contain diminished chords.
Diminished chords are highly unstable and seek resolution more so than major or min. Think dark and you are on track.
Two contain augmented chords.
Augmented chords have a tense sound too that also seeks resolution.
Another chord type not even listed above is the Suspension chord.
sus2 and sus4 chords which offer a suspenseful sound.
Yet another chord type, the power chords. neither major nor minor
only 2 of the three notes of the triad are used (no 3rd) so the melody usually defines major or minor tonality.
Now depending on genre a lot of modern composers who aren’t bound by the laws of functional harmony mix and match chord sets otherwise known as borrowing chords. I think the days of worrying or being forced to use one chord type over another are well and truly numbered. Thankfully.
Unless you want to sound all arty and classical.
Summary
maj=happy
min=sad
augmented=tense
diminished =angry
sus2/4=suspense
power=neutral
its fair to say music isn’t like mathematics it comes more from the heart so any attempt to over formulize it will more than likely sound too mechanical or predictable for the listener.
So the mix and match approach (trial and error) is the way forward imo.
By the way heavy metal or heavy music more often than not uses power and harmonic minor chords with melodies from all manner of exotic scales.
Trance uses the natural minor (aeolian) with borrowed chords a lot to get that euphoric sound.[/quote]
really good post did you post this on another site 
