Harmony and Dyads
Music is more than just scales and melody. Musicians combine notes to produce different moods and ideas in music, and each combination of notes provides a different flavor. Whenever two or more notes are combined (sounded at the same time), we call it harmony. And the pitch space between them is called an interval.
You'll remember in the scales section earlier that each interval has a name based on the distance between the two notes. Here is that list of intervals again:
Each of these intervals has their own unique sound, though some of them are related. First of all, any interval that is the same just an octave wider is related. For example, the major 3rd and the major 10th sound very similar. But even within the octave there are related intervals. For example in key of C, there is a minor 3rd interval between E and G. But if we flip the interval upside down (so the G is in the bass), the interval is a Major 6th. These intervals sound more closely related to each other than to others. If we flip all the intervals within an octave, we see these related pairs:
And here are all the intervals with their related intervals and the intervals octave higher that are related:
Intervals either sound consonant or dissonant. That is, they either sound comfortable when played together or tense. The reason they sound either consonant or dissonant has to do with how their wavelengths relate to each other. Intervals with wavelengths in simple ratios sound more consonant. Intervals with more complex ratio relationships sound dissonant.
For example, the C that vibrates at 261 Hz has a ratio of 3:2 with the G that vibrates at 392 Hz. (A 3:2 ratio means multiply the first number by three and the second number by two and the two products will be the same.) This is the fifth interval and it always sounds the same whether it is C and G, A and E, Bb and F, etc. The ratio is always 3:2 and so always has the same character. And because 3:2 is such a basic whole number ratio between the wavelengths, the sound is very stable and consonant.
The C at 261 Hz with the B at 247 Hz however, does not sound so consonant. This is a minor second interval and the ratio is around 16/15, which is not very stable. The wavelengths of the two notes sound very dissonant and out of tune.
Below is the list of sounds in order of most comfortable to least. Notes from C Major are used as examples, but the ratios of these intervals are the same no matter what key you are playing in, even if the frequencies of the notes change.
*Note that these ratios are approximations. If every interval were tuned in perfect whole number ratios, the last interval tuned would be out of tune with the first interval tuned. This last interval is known as the “wolf interval.” It is why true “Pythagorean” style tuning has been abandoned on modern instruments. Today keyboard and stringed instruments are usually tuned with equal temperament between each semitone. This causes each interval to sound a little off, but avoids having one completely useless interval in the mix. For more information on this, check this link: "JUST INTONATION."
Playing the Dyads
In rock and country music, a lot of steel guitar playing consists of 2-note harmonized parts. These two-note parts are called dyads.
Dyads are where the steel guitar’s capabilities really start to get interesting. The steel guitar is one of the few instruments that allow one interval to be turned into another without any disruption in the sound of the notes, so that all the continuous minute pitches are heard between the pairs of notes. Even the most advanced electronic music production equipment cannot perform some of the dyad sounds capable on the steel guitar in real time.
Because dyads make up such a large part of steel guitar playing, it is important to memorize where they are located, how to play them, and what they sound like. There are a few ways to play dyads on the steel guitar, among these are bar slants, pedal usage, and pedals used in combination with bar movement.
Before the pedals and levers were added to the steel guitar, bar slants were necessary to play certain harmonies.
A bar slant is just what it sounds like; the bar is placed on the strings at an angle so that two different frets can be reached with the same bar. The problem with bar slants is that accuracy is difficult and notes that are more than two frets apart from each other are almost always impossible to play.
Today, we can use pedals to accurately change from one dyad to another. And we can use pedals in combination with bar movement to make wide interval changes. Bar slants are still used on occasion by steel guitarists today, but it is primarily to acquire a harmony for which no pedal exists. If you are playing a student model, or your tuning differs from mine, you may need to use bar slants to acquire certain dyads that I play.
In this example below, strings 5 and 8 are struck at fret 8. Then the lower part of the bar is held steady over fret 8 while the upper half of the bar is slid up to fret 10.
In this example, strings 6 and 8 are struck. Part of the bar is held at fret 8 while the other part is slid down to fret 7.
Using the Pedals.
Pedals have been on the steel guitar since the 1940’s, but it wasn’t until the fifties that steel guitarists began using the pedals to change from one interval to another without blocking the sound between the two intervals. The quintessential steel guitar sound is attributable to this technique.
Here are some examples:
The dyad above moves a major 2nd interval (C-D) to a Major 3rd interval (C-E). This is one of the most used dyad movements in steel guitar playing, and can be played at any fret (depending on the key of the song) on the same two strings using the same two pedals.
This moves a perfect fourth interval (C-F) to a Major third (C-E). This is another very common played dyad movement on the steel guitar.
This moves a minor 6th interval (EC) into a Minor 5th interval (FB). The interesting part about this movement is that the notes are moving in opposite directions. The E moves up a semitone to F, while the C moves a half tone down to B. This is the stuff steel guitars are made of.
As you may now begin to see, there are numerous ways to change from one harmony to another on the steel guitar. Every set of two strings offers a different way to change from one interval to the next.
Using Pedals and Bar Movement.
Just using the pedals alone allows a variety of dyad playing, but we can also use bar movement in combination with pedal movement in order to create unique sounds. This adds another level of complexity to the instrument, but allows for the production of interesting sounds not possible on other instruments.
This move turns a Major 6th interval (FD) into a minor 6th interval (BG). These notes (GBDF) make a dominant seventh chord. The great thing about a dyad move like this one is that you can play the notes of the G7 chord in smoothly connected parts instead of as one clump of chord notes, as you would on a piano for example. This further makes the steel guitar unique in its approach to the creation of harmony.
Steel guitarists often use harmonized scales. These are dyads that are in scale order. They are often used for solos or other melodic parts. Harmonized scales can be composed of any intervals of the scale, but are usually thirds and sixths.
Harmonized scales can be played in two ways: either vertically, across the strings with one bar position, or horizontally, across the neck with bar movement.
Vertical Harmonized scales.
Moving through a harmonized scale vertically can be slow and cumbersome. Look at the example of playing harmonized thirds in the key of C at the 8th fret.
Notice how much room there is for error. You have to depress different pedal combinations and move your fingers to different strings, some adjacent to each other, while others are not. What's more, you cannot play all these harmonies smoothly into each other.
This is why it is easier to play harmonized scales across the neck of the instrument (horizontally). That noted, there are going to be times when some vertical dyad movement will be necessary for certain musical passages.
Horizontal Harmonized Scales.
Horizontal dyad playing allows for quick movement through a harmonized scale. It also allows for every dyad (even the entire scale with one pick strike) to be smoothly played into the next. Many of the unique steel guitar sounds result from playing harmonized scales in this way.
Here are 2 locations to play harmonized thirds in the key of C:
Here are 2 locations to play harmonized sixths in the key of C:
These are just some of the locations for harmonized thirds and sixths. There are obviously many more ways to play these scales on the steel guitar.
Harmonized scales can be comprised of intervals besides thirds and sixths. Tenths, seconds, fourths are all used. And of course there are many different ways to play these scales as well.
The examples above show harmonized scales for the diatonic (Major) scale, but they can be played in other scales as well, such as the diatonic minor scale, the harmonic minor scale, etc. Sometimes these harmonized scales don’t sound quite right, though. For example, even the natural minor (Aeolian of the diatonic scale) sounds a little off when played in harmonized thirds. It is for this reason that centuries ago musicians developed the harmonic minor scale. The harmonic minor raises the 7th note of the scale and as a result adds a stronger sense of resolution to move towards the root note dyad.
Other scales may sound a little off when harmonized, particularly non-diatonic and exotic scales. But these scales can be altered like the natural minor in order to make them more appealing. Some of them already have different harmonized parts that have evolved into them over the centuries. Others are harmonized in many different ways.
Pentatonic Harmonized Scales
Pentatonic (and hexatonic scales) are not usually played as a series of harmonized thirds. The reason is simple, there are not third intervals to harmonize every note within the scale.
Pentatonic Harmonized Scales.
Many times players will harmonize the pentatonic scale by combining the notes that are one note apart from each other. So in the A minor pentatonic the root notes would be: ACDEG. And the harmonized notes would be: DEGAC.
This leaves a harmonized scale that looks like this:
The resulting intervals are a fourth, a major third, and 3 more fourth intervals. All the fourths cause the harmonized pentatonic to have a very ambiguous sounding harmony.
Another common practice is to harmonize freely, using any intervals among the scale to be harmonized with any other note. So A is harmonized with C or G or E. The D is harmonized with A or G, etc. This allows for major second harmonies, sevenths, sixths, minor thirds, major thirds, etc. Whatever sounds good is played.
Hexatonic Harmonized Scales
Hexatonic (and pentatonic scales) are not usually played as a series of harmonized thirds. The reason is simple, there are not third intervals to harmonize every note within the scale.
Hexatonic Harmonized Scales.
The hexatonic scales have been harmonized by players in the same way. The Country and Blues scales have an interesting practice however. The Blues scale in A minor is spelled: ACDD#EG.
But it is usually harmonized like a normal pentatonic, without the D#. When the D# is included, it is treated as a passing tone and harmonized with the A, C, or G.
In other words, the Blues scale is usually harmonized like this:
But the D# is included as a passing note so that it can be found harmonized with any A, E, or, G. Here are some harmonizing possibilities of the blues scale:
D   D#   E
A   A     A
G   G     G
D   D#   E
A   A     A
D   D#   E
But again, like with pentatonic harmonizing, anything goes with the blues scale. If the harmony sounds good then it will be played. In fact, sometimes notes that are not found in the scale will be used to harmonize depending on the context of the tune.
Since the major pentatonic and country scales are comprised of the same notes as the minor pentatonic and blues scales (just starting on a different note), the same rules for harmony apply.
Beyond two-note harmonies.
Music is not just two part harmonies, as you may know. Melodies can be harmonized with many notes (called “voices”). When more than two notes are harmonized together, it is called a chord. Chords are the topic of the next section.