As great as pretty harmonies and soaring melodies can be, sometimes you need a much more raw and chaotic effect. If you're scoring a chase scene you might want to have quick sharp stabs at unexpected and random times. Or perhaps you're working on a free jazz album and want to give every player complete freedom to blurt out whatever musical idea comes into their head.
A simple but effective way to maintain stability in an otherwise chaotic and random texture is to use a sustaining element. Very often in orchestral music it is something soft and unobtrusive like a french horn or tremolo strings. In electronic music it could be a pad or soft synth. In jazz even just a steady beat on the ride cymbal is enough to maintain order and keep your music grounded.
The problem with random and unexpected elements is that it's difficult for your listener to understand what's going on. They don't know what to expect next, and while that can keep them on the edge of their seat for a brief period, if it goes on for too long they'll become bored and disinterested.
Let's look at a few examples of using a sustaining element to act as an anchor for otherwise random and unexpected events. In all three examples I'll play you the random part first, and then we'll see how just a simple sustaining element brings it all into coherence. None of these examples are going to be especially musical, but they should all show the concept of added stability.
Drums and Strings
Our first example is a film score staple: big accented toms. These big drums are great for excitement, energy and masculinity. Playing a drum groove is completely inappropriate if you're trying to convey a sense of fear and excitement, so we need to keep people a little more on their toes:
A little too random perhaps? I'm less excited and more just annoyed. So let's add some tremolo strings, in octaves around mid-range.
The strings add just the right amount of stability that our drums no longer feel like they're whacking us over the head from out of nowhere.
The next example is simply a few shakuhachi licks and some ambient percussion:
Although the effect is somewhat zen, on their own these elements feel a bit empty and lonely. If we simply add a low pad underneath we can create a much larger ambient space and give the shaku and percussion a bed to play over.
Our last example will show that you don't necessarily need your sustaining element to serve a harmonic role. Using percussion can be just as effective as keeping everything stable. Here I've played a random and rather meaningless keyboard and bass part, imagining that these are two guys whose heads are way off into the clouds.
Now all we need to give the illusion of bringing them back to Earth is a steady and reliable ride cymbal pattern:
OK so the whole thing is a little 70s, but hopefully you get the idea.
If for some reason you have a need for random elements, or you simply have ideas that don't fit in nicely to a rhythmic grid, consider adding a sustained instrument underneath as a supporting element. Often that anchor is all you need to give your chaos just enough sense of order.