Aleatory has its genesis in Latin as aleator – a dice player which, in turn, comes from alea, the singular of dice, i.e. die. Aleatory art (or, to be 60's hip, aleatoric art), therefore, is based on randomness, like the throw of a die.
While there are sixty-three and two-thirds (an aleatoric number I just made up) variations on the theme, aleatoric music has some component of randomness. Similar to the idea of improvisation, but with a major difference: improvisation generally is done in a restricted manner. Improvisation is accomplished by being in the same key or mode of the song being played. It has a rhythmic relationship to the song, as well. This makes it 'fit in' to the song and yet allows for a more performer-varied expression and latitude than playing just the melody 'as written'. The genre of Jazz exhibits the most frequent use of improvisational technique. Frequent as in always.
Three broad, basic concepts exist for aleatoric music: unrestricted composition, semi-restricted composition and restricted composition. Improvisation essentially falls into the last category, restricted composition, because the song's key, tempo and rhythm limit the choices to something considerably less than randomly distributed notes, tempos and rhythmic structure. Even if the song goes through tempo changes, key changes, or whatever the composer throws out, the improvisational aspect follows along, changing its key, tempo and rhythm in sync.
Semi-restricted composition can be thought of as an extremely loose improvisation. For instance, the song's composer might indicate a chord outline for the piece and leave the details of individual notes, tempo and rhythm up to the performers. While this could end up sounding like two cats fighting in a metal garbage can rolling downhill, most experienced musicians actually have some sort of unspoken connection, very similar to the practitioners of stage improv, where actors play a scene only knowing a limited amount of information (Abe Lincoln and Mel Torme meet on a subway in New York City. Go!). It can lead to a very surreal experience for both the performers and the audience.
Unrestricted composition is the easiest to implement with a computer. Unrestricted means just that: no rules. Any note can be played at any time with or without any rhythm and tempo, or all those attributes can change from note to note. Needless to say, it can be “interesting” (in quotes, italicized), as we will see, and resembles the music I wrote when I first touched a piano at age 5. Meaning I hit random keys and made a lot of noise.
Even if you don't play piano, you probably can quickly see there are two groups totaling five black keys that repeat. So, take one die and roll it, then hit one of those five black keys. If you roll a six, that's a rest, or pause, and no note is played.
Even though it is called 'unrestricted', in fact there are still some restricted parameters in this composition type. Our tiny example limits the player to 5 notes, rather than the full 88 notes available on most pianos. Adding dice would lift that restriction, at the cost of sounding less like music and more like me at the piano, at the age of 5. The restriction imposed by our black-key die example limits the notes available to what is known as the pentatonic scale. Generally, you can't make displeasing music if you stay on just those five notes. You can even hit 2 or 3 of them at the same time and have a halfway decent sound.
I bring that up because it is the main theoretical postulate of what we will be doing here. To state it in simple terms, by judiciously choosing what rules to follow, we can have a computer make some pretty interesting music.
But, like me as a five year-old, we have to start somewhere and work our way up. So, next blog, we'll see the simple hardware we will start with to create what I call “Arty, The Aleatoric Arduino”.