I just got a TC Quintessence harmony pedal, and I was surprised to learn how it creates third-above harmony notes when set to the natural minor scale. The idea of the effect pedal is to create harmony voices for any notes fed to the input, and this is done by specifying a scale and one or two intervals, for example C natural minor and a 3rd up. This is simple and works as expected, as long as the input follows the set scale. However the input doesn't have to be restricted to the specified scale, and the pedal will produce something for notes outside the scale as well. For the example of a 3rd above in C natural minor ("aeolian"), the note mapping goes like this: (not caring about enharmonic spellings)
- input:C, harmony:Eb
- input:C#, harmony:E
- input:D, harmony:F
- input:Eb, harmony:G
- input:E, harmony:Ab (!? why not G?)
- input:F, harmony:Ab
- input:F#, harmony:A
- input:G, harmony:Bb
- input:Ab, harmony:C
- input:A, harmony:C# (!? why not C?)
- input:Bb, harmony:D
- input:B, harmony:Eb (!? why not D?)
My question is, is there a music-theoretical justification for harmonizing E, A and B with major thirds like that? Is there perhaps a style of music, a tradition or genre, where E, A and B would be harmonized with major thirds, if a minor key is assumed? Or is it just an arbitrary choice, perhaps for technical, not musical reasons. Because for practical situations it would be vastly more useful if E mapped to G instead of Ab, so that it would harmonize well in melodies that temporarily use C major and an E melody note, which is a common pattern. And if A mapped to C and B mapped to D, the same scale would somewhat support melodies using harmonic and melodic minor as well as natural minor. The mappings for C# and F# are actually good, because a C# is quite often used in a C#dim7/C -> Fm motion or C7b9 chord, and F# is often used e.g. in a D7 -> G7 motion.
The way E, A and B are currently programmed, it's hard to come up with any song or practical situation where those harmonies would make sense. But maybe they make sense in theory, and there's just something I don't understand? I've been trying to get my head around the "TonePrint" programming thingy, and I'm feeling that maybe I just don't understand the theory. They have all sorts of fancy scales like "Super Locrian", but these are not really explained anywhere, and playing out-of-scale notes usually produces musically meaningless harmonies.
Why I suspect there might be a theoretical justification for why my idea might be better is, the "bad" notes are exactly those ones that are flattened compared to C major. C minor has three flats: Bb, Eb and Ab. And the way TC has handled the out-of-scale notes, each of them is mapped to the previous lower in-scale note's harmony, plus one semitone. But that's not very musical IMO. Another interesting thing to notice is that all of the bad notes are major thirds (or four semitones). If those were minor thirds, then all five out-of-scale notes would be better harmonized with minor thirds above. Maybe in the style of music I'm playing, the only reason to use non-diatonic notes is to imply a diminished chord? Looking at the reasons why I'd like to have it that way, is exactly that - in pop melodies I use out-of-scale notes almost exclusively to do a dominant (or predominant) and then a dim chord is the right thing to use, thinking that D7 ≈ F#dim etc.
(Also feel free to tell if you know of other harmonizers where a third-above in a minor scale works or can be made to work like I explained)
Edit. I asked about this from TC Behringer's support, and after a couple of rounds of getting irrelevant copy-pasted text from user manuals they said that the behavior cannot be changed and that's it. Well OK, the customer support person was about a light-year away from being able to give any sort of musical justification for why the pedal does what it does.
For comparison I tested the competing (decade-old) Boss PS-6 pedal at a music store, and its handling of the five non-diatonic notes in "minor key" mode was not 5/5 either. And its sound quality is like a generation behind. So far I haven't found any sensible reasons behind any of this stuff. Probably they just didn't think about the whole thing.