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Un­der­stand­ing and us­ing ba­sic tonal har­mony

Computer Music - - Tutorials -

1 Mostly, Western tonal mu­sic is writ­ten ei­ther in a major or mi­nor key. I’ll start by look­ing at major keys. Let’s start with a C major scale – eight notes from C to C, played on the white notes of the piano key­board, to keep things sim­ple for a mo­ment – C D E F G A B C. The pat­tern of in­ter­vals be­tween the notes in this scale is what gives it its major qual­ity.

2 Here, we’ve har­monised the scale by stack­ing thirds up on top of each scale de­gree. This re­sults in a set of di­a­tonic chords – C, Dm, Em, F, G, Am, Bdim and C. The notes in each of the chords are taken from the par­ent scale of the key we’re in. Since this scale is C major, that makes th­ese chords di­a­tonic to the key of C major.

3 We can la­bel th­ese tri­ads with Ro­man nu­mer­als, from 1 to 8, so that we can de­scribe chord pro­gres­sions with­out wor­ry­ing about be­ing in any par­tic­u­lar key. Up­per­case nu­mer­als are used for major chords, and low­er­case for mi­nor and di­min­ished chords. So that gives us I, ii, iii, IV, V, vi, viiº and I, as shown here.

4 In tonal mu­sic, the way a chord works within the con­text of a mu­si­cal key or har­monic pro­gres­sion (se­quence of chords) is known as its har­monic func­tion. Each chord in a pro­gres­sion will be there to per­form a spe­cific func­tion, like set­ting up the next chord or in­creas­ing a feel­ing of in­sta­bil­ity. There are three kinds of har­monic func­tion: tonic, pre­dom­i­nant or dom­i­nant.

5 So, in tonal har­mony, ev­ery chord in a di­a­tonic set has a spe­cific har­monic func­tion. For in­stance, the ii and IV chords have a pre­dom­i­nant func­tion, mean­ing that they cre­ate a bit of ten­sion, but not much. Their main pur­pose is to get you to the dom­i­nant chord in a pro­gres­sion. As an ex­am­ple, here’s a IV - V pro­gres­sion in the key of C major: F major - G major.

6 In con­trast, the V and vii chords have a dom­i­nant func­tion, mean­ing that they cre­ate a lot more ten­sion. The main func­tion of a dom­i­nant chord is to get you from a pre­dom­i­nant chord to a tonic chord. In the key of C major, the V chord is G major, which re­ally has a sense of want­ing to go back to the tonic chord, C major.

7 The I, iii and vi chords have a tonic func­tion, which essen­tially means that they have no ten­sion at all, but are used to re­solve the ten­sion from the other chords. It’s easy to see how the well-known ii-V-I pro­gres­sion, used so much in jazz, came about – it fol­lows the or­der pre­dom­i­nant, dom­i­nant, tonic, or in C major, D mi­nor - G major - C major, as shown here.

8 So tonal chord pro­gres­sions are made up of chords whose func­tion it is to drive the pro­gres­sion along to­wards the tonal cen­tre, or tonic. To show how one chord’s func­tion changes ac­cord­ing to the key we’re in, a C major triad will have the tonic func­tion in the key of C major, the pre­dom­i­nant func­tion in G major, and the dom­i­nant func­tion in F major.

9 Let’s now look at mi­nor tonal­ity with a piece in C mi­nor. The di­a­tonic chords Eb, Ab, Bb for this key are Cm, Ddim, Fm, Gm, and Cm – all chords built from the C mi­nor

Eb Ab Bb scale (C D FG C). The har­monic func­tion is un­changed re­gard­less of the major/mi­nor make-up - i, III and VI are tonic, iiº and iv are pre­dom­i­nant, and v and VII are dom­i­nant.

10 Our ex­am­ple piece con­sists of some drums, a synth bass part and a synth melody play­ing notes from the C mi­nor scale. We’ll har­monise the melody by choos­ing chords from the di­a­tonic set.

Bb Since the bass is just play­ing C and notes, this should fit nicely with our di­a­tonic chords, so let’s go for the tonic as Eb- the first chord, C mi­nor ( G-C).

11 We want a four-bar se­quence to wrap around to Cm again, so after two bars of Cm, we’ll pick a pre­dom­i­nant chord to go in bar 3. The iv chord of the key of Ab- C mi­nor, Fm ( F- C), fits the bill nicely. This would log­i­cally be fol­lowed by a dom­i­nant Bb- chord in bar 4, so we’ll use Gm ( G- D), the v chord of C mi­nor.

12 As the se­quence rolls around to bar five, the re­cur­ring Cm chord re­solves the ten­sion pro­vided by the Gm’s dom­i­nant func­tion. And this time round, we’ll make a slight change - we keep the two bars of Cm in bars 5 and 6, and re­peat the Fm in bar 7, but in­tro­duce a new fi­nal Bb Bb­dom­i­nant chord in bar 8, ( F- D) - the VII chord in the key of C mi­nor.

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