One of the sounds that best characterizes the blues, especially in the second halve of the last century, is related to the use of the bichords, particularly in guitar and keyboard riffs. A bichord is a simultaneous group of two sounds, that usually go up the 1st and 5th degrees of a scale. Looking at the following example, you can see how we can extract two notes, the 1st and the 5th from the scale of C major, obtaining the bichord of C.
According to the rules of musical theory, this cannot be considered a chord, because it only contains two degrees and not three. Remember that a chord must have at least three degrees.
We must consider the fact that the purpose of a bichord is to identify the form (major or minor) of the chord.
The exact definition of a bichord is the C5, which is made up of the C note (keynote) and G (5th degree).
A bichord can also be defined in the fundamental position when the keynote is low, but is defined as the reverse position when the low note is of the 5th degree. In the example below we can see a series of bichords in the fundamental and reverse positions.
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Rock uses the Power Chords, which are from bichords where one of the two degrees are doubled. Using an example in C, we can have a power chord formed by notes C, G and C or G, C and G (reversed). Both degrees can be doubled, playing doubled bichords. In the figure to the right you can see the various Power Chords in C. |
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After the introduction on theory, we will now see how to work with bichords directly within our blues sequence, playing a chorus in C.
We begin with the basic bichord, which is formed by the keynote and the 5th degree, and is developed on a shuffle rhythm and played with down picking. As you can see from the score, the execution is very simple because we only have three different bichords to work with (inherent to C) which are C5, F5 and G5.
Listening to the base midi you will realize how normal this sound is for this type of accompaniment. As always, for the first few times play it slowly.
The basic structure of the bichord can be amplified working on the scale notes of that bichord. In the harmonic environment typical of the blues, the bichord is extracted with the mixolidian scale (in C: C-D-E-F-G-A-Bb-C), and conceptually this is also valid for the other chords in the basic harmonization of the blues.
At this point we can analyze how the structure of a bichord evolves, looking at what is called a riff.
Lets observe a beat with shuffle rhythmics on the C bichord and replacing the G note (5th degree) of the second and fourth movement of the beat with the A note, which is the 6th degree: the bichord of C5 is now harmonized in a bichord of C6. We get a classic blues riff using the fifth bichords, seen in the example on the left. The example on the right is fifth alternated to those of the sixth.
Obviously, as already stated before, even the other chords can be varied. One of the qualities of the guitar is the possibility to transport the fingerings along the fretboard, varying the tone maintaining the same configurations for the left hand. Like this you can easily play the following blues in C, using fifth and sixth bichords.
As always, you can listen to the base midi, to evaluate how you did. In the next page, we will study the construction of some typical blues riffs, based on the use of bichords.
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