Background: A program that generates common chord progressions given a key. For example, in the key of C major, one of the popular progressions we have is I – vi – IV – V (C – Am – F – G). My goal is to render these 4 chords from the neck of the guitar onto the screen.

Let's say I have a C chord and I want to figure out playable positions for it on the guitar fretboard starting at the open string position. The C major triad consists of [C, E, G]. I came up with the following chord that marks all the [C, E, G] notes from fret 0 (open string position) to fret 3

Now this is obviously wrong but It has all the required notes by the C major triad (please disregard multiple notes on the same string, as I am still working on this program). Is there a set of "rules" or heuristics I can use to figure out which fretted notes sound good as a chord while played together with other chords in the progression? For example, if I play the C chord from above, then Am, F and G, it sounds a bit dissonant compared to playing x32010 which sounds a bit cleaner. I think one of the rules is that the chord always needs to start at the root position, this would eliminate the low E string, because the root note is not E or G.

Do inversions play a role in this?

  • What makes it 'wrong'? It may not be the 'standard' open C, but it's a voicing I've played for years. There's also nothing 'wrong' with not having the root as the lowest note.It could even have an open bottom string, and still not be 'wrong'. Also what sort of 'set of rules' are you in search of? If there is a rule, it'll be 'play the notes that belong to the chord - if possible, mute all others'. – Tim Jul 12 at 5:56
  • Wrong in the sense that it’s not x32010 chord. This for a computer program I am building and it needs to produce correct chords, or at least what people consider correct. – hyde Jul 12 at 6:01
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    I'm questioning the term 'correct'. A lot of guitar sites only show root position chords - that doesn't make them 'correct'. Most jazz guitarists would agree with that! A lot of guitar sites seem to not recognise the existence of flats, using only sharps. That again isn't 'correct' - for a good reason! 'Correct' doesn't equal 'root position'. – Tim Jul 12 at 6:05
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    @user1079505 - the diagram shows options for all notes playable in open position. There are two options on each E string - open or 3rd fret. – Tim Jul 12 at 8:38
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    @piiperiReinstateMonica - I believe so many of the 'guitar' sites are trying to brainwash us into thinking the root position is the only one guitarists ought to play. Or do they simply just not know any better? – Tim Jul 12 at 9:49

The rules are thus:

  1. Can you play it? Like, physically, can your fingers reach the notes and can they do so consistently in the context of a song as chords are changing? This sounds obvious but it's important because sometimes "closed" voicings can be tough on a guitar fretboard especially when you get into seventh chords. This rule invalidates your "always needs to start at the root position" premise. Inversions and "drop" chords are essential both for voice leading and the simple practicality of being able to reach all the notes. You only have 4 fretting fingers and the fact that you can only sound 1 note per string makes compromises necessary.
  2. Does it sound good? Some voicings, even if they technically contain all the required notes, don't sound good. Sometimes it's because two notes are too close together, sometimes it's because a certain note doesn't sound good in the root, and sometimes the register just makes it sound too muddy or shrill. Also the context is important. You usually want to "voice lead" the changes which means to consider each individual note as its own voice or part that should change either minimally or melodically as the chord changes. For instance imagine your four fingers are a barber shop quartet each singing their own part. Each finger should form a melodic line but together they should form a chord. In practice, this usually means that if two adjacent chords share a note, then that finger should stay put and the others should move as minimally as possible. But what does your ear say, does it sound good?
  3. Does it fulfill the functional harmonic purpose? You don't have to include all the notes. For instance you might read somewhere that a 13th chord includes the 1, 3, 5, 7, 9, 11, and 13. But, in reality, that rarely happens. You might have 4 or so of those notes that conveys that chord. And that chord is one of a series where one chord leads to another for a harmonic purpose. It serves a function in that it leads you to the next chord and the totality of which leads you from beginning to the end making a meaningful harmonic progression. So, did you include the notes that fulfill that? In other words—even outside of functional harmony—the song calls for a particular chord for a particular purpose. Does it fulfill that purpose?
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  • @hyde "This is for a computer program I'm buidling". Let me just say as both a programmer and a musician, these rules make your task admirable but futile. It would be a nice problem to solve programatically but it requires too much art, for lack of a better word. – user66401 Jul 12 at 7:23
  • A better way to put it might be that context matters and the permutations of which make a simple dictionary of playable chords unhelpful. A chord might be playable physically and it might theoretically be a CMaj chord. But that doesn't mean it will be sound good. There have been books upon books of chord dictionaries that have failed to provide much purpose for the same reason. – user66401 Jul 12 at 7:24
  • You could narrow down certain rules like the only 1 note can sound per string and the human hand can only stretch so far therefor only these voicings are possible. But from the musician's perspective the context and aesthetic matter much more than you realize and those kind of rules are rarely more helpful than simply playing and hearing them. – user66401 Jul 12 at 7:25
  • For instance it's usually obvious if a chord is too hard to reach or if it sounds bad. Even for beginners it's typically better for them to either use the standard voicings in books that we've all been using for years—for good reasons—or for them to learn how to construct chords themselves and ultimately decide that most of the voicings they already know are at least good starting points—for good reasons. – user66401 Jul 12 at 7:25
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    Why are you commenting on your own answer? You can edit it if you think something is missing. :) – piiperi Reinstate Monica Jul 12 at 9:19

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