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Exploring consonance and dissonance
1 Rather than kick off this month with our usual C major scale, this time round we’re starting with a chromatic scale – all the notes, including the black ones, from C to C on the piano keyboard, totalling 12 in all (well, 13 if you count the high octave of C). 2 I’ve already discussed intervals at some length in previous EasyGuides, so here’s a quick refresher. Every note in the chromatic scale is a set interval, or number of semitones, above the root note. This chart shows the names of all of the intervals that occur in an octave. 3 Intervals come in two categories – consonant and dissonant. The consonant (ie, pleasant-sounding) intervals can be further separated as perfect and imperfect. Perfect consonances include the perfect fifth and octave, while the major third and sixth are in the imperfect camp. 4 Dissonant intervals include the minor second (a single semitone), major second (two semitones) and major and minor sevenths. Let’s not forget the evilsounding tritone, too, also known as the augmented fourth or diminished fifth – an interval of six semitones, or exactly half the octave. Played out of context, these intervals sound jarring and unsettling. 5 We can put this theory to good use. For a second, let’s compare dissonance to, say, chilli powder. Eat it by itself, and it’s not a very pleasant experience. Add a dash of it here and there to other dishes, though, and it can make all the difference. To illustrate, here’s a short, single-note melody containing notes taken from the C major scale. 6 I’ll harmonise the notes in two-part harmony, but using only dissonant intervals. It now sounds like something out of your worst nightmares. This is an extreme example, though – remember the chilli analogy? Dissonance can be thought of as musical seasoning – if we didn’t use it at all, music would be extremely bland.
7 Here’s the same tune harmonised with more consonant intervals. It’s much more cheerful, due to its major key and consonant intervals between melody and harmony. But, note the second and third notes, D and E have been harmonised with minor thirds – dissonant intervals. They work here, as they use notes diatonic to C major, the key we’re in.
8 One of the most common everyday ways we use dissonance is when voicing extended chords. Take a major seventh chord, for example. The regular voicing of a major triad goes root, major third, fifth – all consonant intervals. Adding a dissonant major seventh shouldn’t work, but it makes a much more grown-up chord in the shape of the major seventh.
9 The example you can see above is Cmaj7 – C, E, G, B. If we were to invert the chord to the second inversion, by moving the lowest two tones up one octave to get G, B, C, E, we would get a cluster of two notes in the middle of the chord – B and C – that are effectively separated by an even more dissonant minor second interval.
10 Here’s a short progression in the key of A minor – the relative minor of C major. We’ve got the chords F major - E minor - E minor - F major. Currently, the chords are voiced as regular triads, containing just the root, third and fifth of each chord. So, with the exception of the odd minor third, the intervals are therefore mostly consonant.
11 To spice things up, I’ll add a major seventh melody note ( E) to the top of the first F major chord, making Fmaj7. I slip in a passing Dm7/G chord to underpin the melody, before adding a C to the first Em chord and raising the bass note from E to
A to make an Am9. The dissonance here is the minor second interval between the B and C notes.
12 In the second of the Em chords, I use the melody note of D to effectively move the consonant fifth ( B) to a dissonant minor seventh ( D), destabilising the chord a little and giving it the character of an Em7. Meanwhile, the final F major chord receives a G note between the F root and the melody note of A, making an F9 chord.