People often get in a muddle about keys, especially those that do not read sheet music. It would be silly to dwell on them in a series focusing on improvisation, but given that they are, essentially, the grounds upon which any song you are going to improvise over is written, some instruction is probably required.
Okay, a song is essentially a collection of notes. These notes relate to each other to form harmony, which is where the music comes from. A key is, essentially, which notes you use. These are the ones that the melody (be it sung of played) uses and the ones that the chords are made up of.
There are two kinds of key: major and minor. Major ones sound happy and minor ones sad, although much of the emotion in a piece comes from composition and not choice of key alone. Let us look at a few examples (NB a note with # after it is raised by one. One with b next to it is lowered one semitone. And a semitone is one fret i.e., the first fret on the 6th string is one semitone lower than the second fret on the 6th string)
Let us consider some examples, just so you know what I'm getting at:
C major's notes are
Notice, also, how the keys are set out. The note the key is named after, which is called the root note or just the root comes first. We give each note a number, normally done in roman numerals, so the key note is I (one) and the second note is II (two) and so on. See below
C major's notes are
A Quick Note About Scales
There's going to be lesson after lesson on scales, but all you need to know now is that If you play a scale, you play the notes of that key in order, most usually ascending then descending.
Chords are a real stickler, but basically govern what you play when improvising and so it's best to tackle them now. Let's look at them as simply as possible:
So, lets say an A chord is being played in the key of C major. A major's key has a C# in it, making in A-C#-E. Yet the key of C major has no C# in it. Crisis! Or not, as the case may be. One simply plays an A minor, flattening the third (C# becomes C) to fit the key signature. This new chord is called an A minor.
And why? Well there's two ways of looking at this. One is simply that, when you flatten the 3rd of and chord, it becomes a minor chord. The other is that, in the key of A minor, chord one (A minor) is A-C-E.
Identifying A Key
It helps a lot to know what key you are in. How can you work this out? Here are a number of strategies:
The Hard Way
Write out all the chords that are used in it, ignoring any that are only used very rarely or that appear to be dissonant (that is, they do not fit with the music), including whether they be major or minor. Compare them to this
Chord Number: 1 2 3 4 5 6 7 Tonality: maj min min maj maj min (diminished, but ignore this).
and see what pattern most likely fits this one.
G major, D major, B minor, A major, in a chord progression, These all fit in if we have D as chord one with the chart above, so it is likely in D major.
If, however, a chord progression appears more minor in its tonality, it is likely in a minor key. Identify its key as above, but then you will have to find the relative minor. A relative minor is the minor key which shares its notes with a major key, for instance, A minor shares its key with C major; simply lower 3 semitones from the major key to find its relative minor.
Hopefully that has cleared some stuff up for you all. I realise there was zero on improvising in this particular episode, however next time I hope to at least introduce some basic scales and ideas that will, eventually lead towards some simple improvisation exercises.