SongTrellis
Music and Musical Know-how For You

Author:  David Luebbert Posted:  2/22/03; 10:36:24 PM Topic:  Voice Leading Msg#:  3498 (in response to 3497) Prev/Next:  3497/3499 Reads:  1198

Gerald,

The MIDI files and scores for nearly all of the changes I've posted to the site were created with the Mac version of the SongTrellis editor. The chord sequences were mostly voiced by the editor using an algorithm I developed. Early versionsof the editor used  much looser voice leading rules which allowed large interval leaps between chords almost always. I learned better music theory after that and coded voice leading rules for the editor that give much smoother results. I started using those new rules in June, 2001.

If you encounter a progression that was submitted before 6/1/01 it's much more likely that the progression will use wider disjunct intervals in the voice leading. If there was something truly unpleasant going on in a progression, I might have manually adjusted the voicings to make them sound better but I didn't have a theoretical basis for making those decisions, so it was hit or miss whether I actually improved the voice leading.

If you follow the "List all chord progressions from newest to oldest" link on The Changes page, you should be able to notice the difference in quality between the pre-6/01 and post 6/01 postings. The old algorithm broke down and did a worse job when chord durations were short or the tempo was fast.

Here's a description of the algorithm in caricature form. In most common chord progressions it ends up that the third and seventh intervals of the chords you play guide your ear to the next chord in the sequence. It's most important to provide smooth transitions between the thirds and sevenths of adjacent chords. Our goal is to align either thirds in the first chord with thirds  in the second chord and sevenths in the first chord with sevenths in the second chord or else thirds in the first with sevenths in the second and sevenths in the first with thirds in the second.  We would like to keep to a minimum the skips between chord notes that serve these functions.

When the roots of adjacent chords move by 4ths or 5ths, you'll find that geometrically the third of the first chord will be within a major 2nd or minor third interval distance of the seventh of the second chord. Similarly, you'll find that the seventh of the first chord will be a small interval away from the third of the second chord.

It does not matter if you wish to place the third or the seventh interval lower in the chord voicing of your initial chord in a sequence. But wherever you choose to place the chord's third in a voicing, if the root motion is by perfect 4th, flat 5, or perfect 5th up or down, you will choose to place the seventh of the following chord as close as possible to the third, which will typically be a major 2nd or less.Whatever register you decide to place the seventh of the first chord, for 4th or 5th root motion,  you will place the third of the following chord as close to it as possible, frequently within a major 2nd in most cases.

If your chord roots move between adjacent chords by less a major 2nd or less, you will attempt to match 3rds with 3rds and 7ths with 7ths between the adjacent chords. Nearly always this maintains a major 2nd distance between adjacent guide tones which gives your ear a nice smooth sensation when you move from the first chord to the second.

If the root motion between chords is a major or minor third it will not be possible to make a minimal sized transition between adjacent guide tones so you are free in this instance to place thirds in the first chord next to either thirds or sevenths in the second chord and to likewise to place sevenths in the first chord next to thirds or sevenths in the second chord.

After determining the placement of the thirds and sevenths, you just need to handle the positions of the roots and fifths in your voicings. Almost always you will play the root as the bottom note of each chord. You will place the fifth according to your taste, lower than, in the midst of or higher than the thirds and sevenths. Using this conception you are pretty likely to produce voicings which will flow smoothly into the next chord of the progression.

To summarize here are the important features of the scheme: keep the roots on the bottom nearly always. Let the fifths float above them as your ear allows. Pay most attention to how you hand off between the thirds and sevenths of your chords. You can start with thirds below sevenths or vice versa. They should both be placed above the root.When you have root motion up or down by 4ths and 5ths, thirds will lead to sevenths and sevenths will lead to thirds. When you have root motion by major or minor 2nds up or down or the roots do not change, thirds lead to thirds, sevenths lead to sevenths. When you have motion by 3rds, minor or major, up or down,  the thirds and sevenths will not line up all that closely, so you can have third leading to third, seventh leading to seventh, third leading to seventh or seventh leading to third according to your taste. This list exhausts the possibilities.

• Re: Voice Leading, Gerald Oplinger, 2/23/03; 4:52:04 PM

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