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The melodic minor scale builds further on the harmonic scale. In the melodic scale both the sixth and the
seventh tone are raised.
However, "officially" the tones are only raised when playing the scale up (from low to high). When playing the
scale from high to low, the two tones go back to their
"normal" state.
In practice, it depends on the situation. In classical music the above rule often applies. In Jazz improvisation however, it depends on how you want to sound (which is beyond the scope of this theory tutorial).
This is A melodic minor up:

And this is the scale when playing from high to low:

This is how this scale sounds:

A Melodic Minor up and down
Next we'll look at some more exotic scales: the whole tone, diminished, octotonic and super locrian scales.