clattering SkyNET chord Konquest tetrachord Lydian Eb submediant Phrygian Locrian tetrachords tritone Bb semitones 52Cr chords flatted chromatic octave semitone hexachord pentatonic bVII sharped nenano supertonic Battloid enharmonic subtonic octaves arpeggio diatonically phrygian stork minor7 tonas cadence HV20 overtype