Power Chords
I do not assume any responsibility for frustration, injury or death resulting from the application of these exercises.
Overdriving or distorting a guitar makes the overtones much more prevalent. On the surface, this creates the warm, glowing sound that inspires us so much and with compression and sustain that masks all the glitches in our playing. However, the overtones don't just add sparkle. They also introduce the risk of interference.
On distorted guitar, even consonant intervals like the third and the sixth introduce a certain amount of beating. This beating is due to a collision between the overtones of the notes.
Basic Power Chords
Therefore, rock and metal players use chord voicings that only contain the simplest frequency ratios as found in the harmonic overtone series: octave, fifth and fourth. These are called power chords.
The most common form of power chord is a two-note chord (dyad) that contains the root and the perfect fifth. The symbol for a root-fifth power chord is the simple, unequivocal C5, D5, F#5, and so on.
There are a few examples of power chords in first open, then moveable (barre) forms:
E5 A5 G5 E5 E-----|-----|-----|----- B-----|-----|-----|----- G-----|-----|-----|----- D-----|--2--|-----|--9-- A--2--|--0--|--5--|--7-- E--0--|-----|--3--|-----
Power Chord Voicings
According to the principles of chord voicings, the upper chord members may be voiced in any way so long as the root remains in the bass. This opens up possibilities for fuller and/or more interesting power chord shapes.
Open E5 and A5 can utilize open strings:
E5 shapes: A5 shapes: E-------------0--0--|-----------0--0-- B----------5--0--0--|--------5-----5-- G-------4--4-----4--|-----2--2--2--2-- D----2--2--2--2--2--|--2--2--2--2--2-- A-2--2--2--2--2--2--|--0--0--0--0--0-- E-0--0--0--0--0--0--|-----------------
The open strings can also be used to reinforce chord shapes that are played higher up on the neck:
E-----|----- B-----|----- G-----|--9-- D--9--|--7-- A--7--|--0-- E--0--|-----
D5 can also be played open, as can C5 and G5:
D5 shapes: C5 shapes: G5 shapes: E--------5--|--------3--|-----------3-- B-----3--3--|-----1--1--|--------3--3-- G--2--2--2--|--0--0--0--|-----0--0--0-- D--0--0--0--|-----------|--0--0--0--0-- A-----------|--3--3--3--|-------------- E-----------|-----------|--3--3--3--3--
The fingering used for power chords is a subtle and surprisingly tricky issue. The fuller shapes are commonly played by barreing the fifth and octave. Watch what that finger is doing. It is all too easy to inadvertently extend the barre so that the 11th is fretted, for a rather distracting sus4 sonority.
Inverted Power Chords
Power chords can also be played in inversion, i.e. with the fifth in the bass:
E5/B B5/F# E-----|----- B-----|----- G-----|----- D--2--|----- A--2--|--2-- E-----|--2--
Adding the lower fifth below the root can create the illusion of a lower string, because of the difference tone creating a perceived octave doubling of the root. In this way, the sound of a 7-string guitar can be approximated, especially together with a 5-string bass guitar.
This type of chord can also be encountered as a melodic variation of the fifth as part of a riff, this one in the intro to Earthshine by Rush:
E---------------|----------------------- B---------------|----------------------- G---------------|----------------------- D---------------|----------------------- A-9-7--9--7-9-7-|-(7)-9---7-10-12-10-12- E-7-7--7--7-7-7-|-(7)-7---7-10-10-10-10-
Conclusion: look for the harmonic context of the chord.
Altered Power Chords
Altered power chords use some other interval than the perfect fifth above the root. Most commonly, we encounter a diminished or augmented fifth, but perfect fourths and major sixths can also occur.
A-5 A5 A+5 A4 A6 E-----|-----|-----|-----|----- B-----|-----|-----|-----|----- G-----|-----|-----|-----|----- D-----|-----|-----|-----|----- A--6--|--7--|--8--|--5--|--9-- E--5--|--5--|--5--|--5--|--5--
It is important not to confuse altered power chords with incomplete inverted triads, such as this progression from E5 to G5:
E----------- B----------- G----------- D----------- A--2--5--5-- E--0--2--3--
In this example, the second chord, the F#-D dyad, is not an augmented F#+5 power chord (which would be written F#-Cx) but an incomplete first inversion D major chord.
Likewise, diminished fifth power chords might imply some form of diminished triad, i.e. an incomplete dominant seventh:
C5 B5 B7/D# E5 E-------------------- B-------------------- G-------------------- D--5--4----7-----9--- A--3--2----6-----7--- E--------------------
Colored Power Chords
Traditional open and barre chords can indeed be used to great effect with distortion, but too much of them and the ears tend to tune it out as a big mush.
Instead, you can try adding certain extension intervals to power chords for a bit more spice. For example, you can add a major ninth, which creates a chord that can be analyzed as a sus2 chord:
Esus2 Asus2 Dsus2 Csus2 Gsus2 E-----7--|-----0--|--0--5--|-----3--|-------- B-----7--|-----0--|--3--5--|--3--3--|-----3-- G--4--9--|--4--2--|--2--2--|--0--0--|--2--2-- D--4--9--|--2--2--|--0--0--|--------|--0--0-- A--2--7--|--0--0--|--------|--3--3--|-------- E--0-----|--------|--------|--------|--3--3--
The minor ninth power chord gets a less clear chord symbol but a decidedly more evil sound:
E5add-9 A5add-9 D5add-9 C5add-9 G5add-9 E--------|--------|-----5--|--------|-------- B--------|--------|--4--4--|--2-----|-----3-- G--------|--3--9--|--2--2--|--0--6--|--1--1-- D--3--9--|--2--8--|--0--0--|-----5--|--0--0-- A--2--8--|--0--0--|--------|--3--3--|-------- E--0--0--|--------|--------|--------|--3--3--