>Step by step

Ex­plor­ing con­so­nance and dis­so­nance

Computer Music - - Make Music Now / Easy Guide -

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.

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