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Im having trouble understanding a concept in Persichetti’s book 20th century harmony (Page 43) where he introduces new scales he calls synthetic scales.
Just before that he talks about the church modes & how you can build chords, and why you should avoid tritones, etc.... with that same concept how do I apply that to a scale like the octatonic scale? Do I still need to avoid the the Tritones for that scale in order to stay true to the mode?

How do I find the characteristic notes in a scale like the octatonic or super Iocrian? He talks about using tetrachords in order to find the primary chords which I kinda understand, but what confused me was when he talks about testing further possibilities of each scale by scanning Intervallic points between the original and mirrored versions of the scale in order to find “hidden potentialities, cadential patterns, passing textures and outer voice movement.”

How do I start this process so I can test and use any scale

  • Take the bog standard scales above like the harmonic minor and pentatonic major scales. How do you (already) use them? How do you answer your questions for those scales? – Dekkadeci Oct 24 at 10:21
  • what I’m asking is how do you find the primary chords for these scales? Should I still avoid the tritone? How do I cadence in a scale like the octatonic scale? – eraserhead Oct 24 at 12:50
  • This is a good question. I might suspect that chords built on these scales may not be as meaningful as those built on Major and Melodic minor. The standard approach of stacking 3rds, or every other note, may start to fail. – ggcg Oct 24 at 16:45
  • Having not read Persichetti’s book, I don't understand why you would be avoiding tritones in any scale. Can you elaborate or give a little context? – ibonyun Oct 24 at 20:01
  • And what do you mean by "mirrored version" of a scale? – ibonyun Oct 24 at 20:10
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I haven't read Persichetti’s book so I maybe don't understand the context of your questions well enough to give you a satisfying answer. That said, I have studied 20C music at length and frequently use all sorts of synthetic scales in my own compositions, so hopefully something I say will be useful.

Terminology might differ by region, but I think in general the term synthetic scale simply refers to any scale that is somehow an artificial construct of the mind, ie invented, rather than having originated "naturally" within a particular music culture (the way the diatonic church modes did in the West). This includes scales which are derived from traditional scales -- eg by altering notes or by combining diatonic tetrachords that don't normally go together -- as well as scales which are invented based on some sort of theoretical principle -- eg symmetrical scales like whole tone or octatonic, which are created by equally dividing the octave into repeated intervalic patterns.

This is a huge and heterogeneous category, so it is difficult to impart general guidelines for how to use them. Which scale are we talking about? What are you trying to achieve musically? Presumably you're not going for functional harmony, but maybe you still want a tonic? In composition, anything goes. The exciting thing about abandoning the rules of common practice music is that you get to make your own set of rules.

To become familiar with a new scale/mode, I suggest noodling in that scale on a polyphonic instrument such as piano or guitar. That way you can explore the harmonic possibilities. If you're interested in having a tonic, then I'd suggest that you drone the tonic while you noodle, because you'll want to hear how each note feels relative to the tonic. If you're really interested in harmony, I'd suggest being systematic.

How to handle harmony? I don't think I can give any generally applicable guidelines here. Literally any combination of notes is a valid chord. Some will be useful and some won't. In most cases, you're unlikely to find chords which will drive your music the same way dominant quality chords drive common practice music. But you might be able to achieve a pseudo-functional effect by resolving intervals (eg tritones) in traditional ways, only in the context of the new scale.

Do I still need to avoid the the Tritones for that scale in order to stay true to the mode?

I don't see why you would need to avoid tritones in any scale. Both tonal and atonal music and full of tritones. Melodic tritones are typically avoided in common practice music, but they're allowed -- even required -- by its harmony.

How do I find the characteristic notes in a scale

Every note in a scale is important. The idea of some notes being somehow "characteristic" of a scale only makes sense when you consider scales relative to each other. Take dorian mode for example. When compared against the natural minor scale its characteristic note is its raised 6th degree, whereas when compared against the major scale its characteristic notes are its lowered 3rd and 7th degrees. Simply put, distinguishing features depend on context. It might not be the scale degrees themselves which are characteristic, but maybe a particular intervallic pattern.

That's all pretty vague, I know, but it's a broad question. Hopefully you'll find some utility in my answer.

  • I understand what your saying, but I’m trying to use these scales while keeping a sense of direction in mind. In his book he explains that the tritone should be avoided because it needs to resolve, just like in a major mode. So in order to keep the sound of the mode the tritone is avoided. So for example if I was in Dorian mode the characteristic note is the raised 6th degree, so therefore the primary chords (or dominant equivalent) are chords with that note because they need to be emphasized. I’m just wondering how to find these primary chords in a synthetic or exotic scale like octatonic – eraserhead Oct 24 at 21:46
  • Ok, I think I understand what you're after. I couldn't get access to this book without paying, but I did find a free summary which was quite detailed. So I now have the context I was missing before. I will edit my answer accordingly when I have time. – ibonyun Oct 25 at 7:23
  • I did a lot of searching and Im starting to understand it now.... if you want I can explain & does this website have an inbox? I can send you a link to the book if you want – eraserhead Oct 25 at 19:27

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