One of my all time favourite scales is the harmonic minor scale. It is just like the natural minor scale but the seventh degree is raised by a semitone.
E natural minor consists of E F# G A B C D E.
Here is how E natural minor sounds
E harmonic minor consists of E F# G A B C D# E.
Here is how E harmonic minor sounds
I love how the D# adds alot of tension and a touch of mystery to the scale. The D# creates tension by wanting to resolve towards the tonic of the scale, the E. Harmonic minor is used very widely in jazz and rock music.
I always have to think of Slash from Guns 'n' Roses when I hear the harmonic minor scale since he uses it extensively in his soli.
Have a listen to the Sweet Child of Mine solo (at 2:34). The first half and the high speed fill are entirely in Eb harmonic minor (it's just E harmonic minor but his guitar is tuned down by a semitone) and then the scale resolves to Eb natural minor which creates the 'release' feeling.
Here is a bit of music theory about why harmonic minor is actually called 'harmonic' - it all has to do with chordal harmony. But don't worry, it's very simple
E major consists of E F# G# A B C# D# and the chords you can build with this scale are
A very classical chord progression is I - IV - V - I, which in E major would be E - A - B - E. Here is what it sounds like
It does have a very classical feel to it doesn't it? I like the tension created by the dominant chord (the B) and the resolution to the tonic.
Now let’s see what happens when we do this chord progression in a natural minor scale. In E natural minor, the chord progression is Em - Am - Bm -Em. Have a listen!
Hm, kinda lacks the tension doesn’t it? That’s because the dominant is actually a minor chord. The chord lacks the D# that would make it a major chord to create the tension and lead back to the tonic of the scale. In order to give this natural minor scale a more harmonic feeling, we need to make the dominant chord (the Bm) a major chord. We do this by raising the seventh degree, the D#, by a semitone – and thus we get harmonic minor.
The progression has the feeling of a minor scale, but the same harmonic tension as the progression for the E major scale. Harmonic minor is a great sounding scale and you can
easily switch between the D and the D# while the harmonies of the song progress over the E minor scale. Have a listen to some other of Slash's soli - he has an amazing feel for when to introduce more tension by using the harmonic minor scale