Understanding keys

So musicians that play together have to agree first on the scale to use (if they want to avoid playing notes that don’t go well together). But this is not enough. They also have to agree on the key they will use. The key (in tonespace at least) is just a fancy word for the starting note or better, the starting pitch class of the scale [4]. A key of C means we start at the first pitch class (being zero). A key of C# means we start at the second pitch class (being 1). A key of D means the third pitch class (being 2). And so forth.

You can control the key using the key parameter in tonespace.

Note: when you hear someone saying : “let’s play in the key of C Major”, actually this says two things at once:

the scale to use, i.e. the intervals between valid notes (Major)

the starting pitch class (C or offset 0)

This means that, starting from C (offset 0), you will use only notes that you find at the relative offsets [0 2 4 5 7 9 11]. For the key of C that starting pitch class would be 0, therefore, for the middle octave which starts at midi 60, we get to keep midi 60+0+0, 60+0+2, 60+0+4, 60+0+5, 60+0+7, 60+0+9 and 70+0+11. This is shown in the space fragment below:

Should you instead agree on D Major, then the intervals would remain the same (major), but the starting pitch class would be different (offset 2), leading to the following midi notes in the scale/key : 60+2+0, 60+2+2, 60+2+4, 60+2+5, 60+2+7, 60+2+9 and 60+2+11. The result looks like this:

Notice how you get the same pattern of allowed notes starting from either C in the first picture and starting from D in the second picture. It is just shifted upward by 2 semitones.

Should you agree instead on C Minor, then the starting note remains the same as C Major (offset 0), but now the intervals that you add to that starting note will be different (minor) : [0 2 3 5 7 8 10], yielding midi notes 60+0+0, 60+0+2, 60+0+3, 60+0+5, 60+0+7, 60+0+8 and 60+0+10. Which looks like this:

So keep in mind that the resulting note selection is always a function of these two things : the scale (the intervals) and the starting note to which the intervals are added. You are encouraged to play a bit with the scale and key parameters in tonespace to get a feel of how scales and keys interact to select a bunch of notes.

Notice also how the underlying space never changes. Applying a scale and key is in fact just putting a filter onto the space, making certain cells black and adjusting the note labels in each cell. It does however not alter the location of the midi notes within the space. Midi notes are an absolute pitch notation whereas scales, keys and note names are relative to the point of view of the musician [5].