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ࡱ > f h e 9 bjbj .F l $ $ 0 > Y0 [0 [0 [0 [0 [0 [0 $ 2 84 B 0 0 p 0 p p p Y0 p Y0 p p &% Q' ' v pB{$ i' ' 0 0 0 q' , z4 z4 ' p $ $ Musical theory of diatonic Inversus
Playing a melody the right way is called Rectus, playing it by inverting the notes vertically around a pivotal point is called Inversus.
Analyzing the Inversus process used by W.A. Mozart, I infer the following rule:
To stay in the same key when going inversus, a diatonic scale is pivoting around its third degree. That note being the central note of the I chord, that chord stays identical when inverted, while the IV and V chords are always interchanged.
Example in the C major scale:
Rectus BCDEFGAInversusAGFEDCB
E is the third note of the scale (C, D, E, F, G, A, B).
Chord I (C major): C-E-G inverts to G-E-C (mirror position of the same C chord).
Chord IV (F major): F-A-C inverts to D-B-G (mirror position of G major V chord)
Chord V (G major): G-B-D inverts to C-A- F (mirror position of F major IV chord)
Applying that rule to a mechanical instrument, we have two cases:
The instrument has an odd number of notes. Inverting the band (or book), the pivoting point falls on the central note. Ex.: With the Sankyo 15k, note C8 stays identical, in unison:
123456789101112131415RectusC DEFGABCDEFGABCInversusCBAGFEDCBAGFEDC
C is the central note of the A minor chord (A-C-E = E-A-C). So we are inverting the scale based on that chord: A minor aeolian modal scale. The V chord E minor (E-G-B) is permuting with the IV chord D minor (A-F-D, mirror position of D-F-A). Ex.:California dream: CalDrmIn.mid
2. The instrument has an even number of notes. Inverting the band, the pivoting point falls between two notes. With the Sankyo 20k, between E10 and F11:
1234567891011121314151617181920Rectus CDEFGABCDEFGABCDEFGAInversus AGFEDCBAGFEDCBAGFEDC
The whole central octave becomes the pivoting point, and B is the actual pivoting note one octave apart: B7 inverts to B14. B being the central note of the G major chord (G-B-D = D-B-G), we are inverting the scale based on that chord: G major mixolydian modal scale.
With that F natural (not F#) the V chord is D minor (D-F-A), inverting to the IV chord C major (G-E-C, alternate position of C-E-G). Ex.:Forlorne: Forlorin.mid
How to invert the important C major key
With an odd numbered notes instrument, the pivot note must be E, so the C major chord will stay the same when inverted: C-E-G = G-E-C.
Imagine the Sankyo 20 noter as being an odd numbered 21 noter. Adding a virtual note (V) in the lower margin (M), E10 becomes the center note, the hinge:
M1234567891011121314151617181920Rectus VCDEFGABCDEFGABCDEFGA Inversus AGFEDCBAGFEDCBAGFEDC
E is the central note of the C major chord. So we are inverting the scale based on that chord: C major scale. (The inverted band moves down the width of a track, since its upper margin has been diminished, as explained in the main text). In rectus, all 20 notes play normally. In inversus, a hole in virtual V will activate the highest A. So we dont loose any notes. Ex.: BrunoInv.mid
If we slide the inverted scale in the other direction, note F11 becomes the center, and we get a scale in D minor, dorian mode, [D-F-A= A-F-D):
1234567891011121314151617181920MRectus CDEFGABCDEFGABCDEFGAV Inversus AGFEDCBAGF E DCBAGFEDC
Ex.: Scarborough Fair (ScarboIn.mid) and So What? (SoWhatIn.mid)
Arranging in inversus is challenging, especially with preexisting melodies.
The permutation of chords V and IV is delicate. I consider the chords as incomplete 4-notes (Dm7=G7, CM7=C6, F6=G7, Em7=FM7). I imagine the accompaniment as an inverted melody on its own. Since the treble notes are heard more distinctly than the bass notes in a music box, the accompaniment is less clearly perceived than the treble melody.
My MIDI examples are just studies to illustrate the inversus, not polished arrangements.
It would be stimulating to hear other arrangers try it.
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