Electronica is quite possibly the most complex and varied of all genres of modern music. On one hand, there's IDM, which has arrangements masterful enough that some would say rivals that of Classical music while at the same time experimenting on the fringes of noise and music. On the other hand, there is the dance-based music of House, Trance, and Techno, with incessant, repetitive, yet catchy and organized collections of sound intended to stimulate the feet as much as the ears. But what makes these two ends of the spectrum of Electronica similar? Besides both having roots in music specifically ordained for dancing, they both have a seemingly mindless attraction to percussion (to the point that such artist as Squarepusher and Autechre have built quasi-melodies based entirely on rhythm). Because of this strong fascination for the rhythm side of music, an entirely new form of composition has sprung up from the Electronica of the late nineties and early aughts.
For a couple hundred years, music of the popular (as in, non-classical) variety has been based on simple "songwriting" structures (i.e. verse, chorus, verse). While Rock from the Prog-Rock era and beyond to an extent has experimented with more "Classical" arrangements (based on movements of music), Electronica has taken a different approach.
If one listens to the typical Trance song, there are immediately two things that come to mind regarding rhythm and song structure. The first is that these songs are usually over six minutes in length. The second is that pieces of the song are usually introduced in a gradual manner. The latter accomplishes two things: by having each instrument come in gradually, a climax is easily reached because the increase in volume and complexity. The second is that former song structures are eschewed in favor of loop-based ]structures.
And finally we get to the topic: loop-based composition. Basically this involves dividing up music into its individual samples. Typically, in computer-based composition, one uses MIDI or data of the arrangement rather than sound files to create music because typically this allows more freedom in the composition.
Once the song is divided into its individual samples, it can be arranged. Programs that are used to arrange loop-based music include Ableton Live!, Fruity Loops, and Acid. Basically one takes each sound and places it rhythmically and structurally to create a whole song.
Bass drum + open hi-hat + clap + bassline + first synth + second synth...
A typical arrangement may look like this:
D = Drums
S = Synth line
St = Synth stab
P = Pad
- = Continuing sample
D------- D------- D------- D-------
S------- -------- S------- --------
St St St St St St St St
P---P--- P---P--- P---P--- P---P---
How is this different than using a sequencer such as Emagic Logic Audio or Steinberg Cubase, one might ask? Well, while it is true that these programs can be used to make music similar or indeed identical to music created using loop-based music programs, loop-based music programs have three important features: looping, pitch/time stretching, and live DJ performance.
But first, some history. In the mid-nineties, a small European software company by the name of Propellerheads released a program called ReCycle that allowed one to take samples such as that of drums and divide them up into beats. What made this so important to modern Electronica is that it allowed one to (almost) seamlessly stretch the samples to nearly any tempo without the pitch changing and with little noticable degrade in sound quality. While it is true that hardware sequencers allowed one to cut up samples, pitch-shifting and time-shifting was always a pain-staking task. However, ReCycle made this a simple task and also simplified such tasks as creating breakbeats (by scrambling the drum beats) and doing such "simple" things as removing syncopation in "funkier" songs for use in more "formal" Trance songs.
Around the same time, a small program called Acid was released. It utilized .wav files with extra data (that could still be used for their original purpose) that allowed them to be used with any tempo without pitch change, or vice-versa. While this was in effect similar to ReCycle, Acid went a step further by not only including a library of samples but also by integrating a sequencer, allowing songs to be created by arranging samples. This was different than other sequencers at the time because of the ability to change the tempo with one mouse click instead of endless effect tweaking.
Many loop-based programs, such as Ableton Live! also allow one to take sound samples divided into measures and loop them, allowing one drum beat to continue playing unabated among multiple measures (this of course can be done to other samples as well). It does this by looking at the beats and fitting them to a measure and then basically duplicating it among multiple measures.
Fast forward to 2002. With the release of Ableton Live! and other live loop-based DJ applications, loop-based compositions have become something entirely different than most likely anyone would have guessed in the mid-nineties. While Trance, House, and other Dance-based Electronica was always largely a live act, it is now not at all uncommon to see laptops as well as rackmount hardware, keyboards, and turntables among the arsenal of dance DJs. Because of looping, beatmatching with turntables has found an easier alternative, and with the advent of pitch and time stretching, tempo can be easily altered with a couple clicks. In addition, samples can be assigned to keys on a MIDI or computer keyboard or even MIDI guitar, (or, by utilizing Antares Kantos, even the voice or any monophonic instrument) and triggered by the keys. This allows for live arranging of songs and allows for a very exciting live element. Of course, plug-ins can be used in a live fashion as well, to create echos and even subtly changing samples over multiple measures.
Because of another piece of software made by Propellerheads (ReWire), many of these programs can be integrated with software synths (like ReBirth and Reason) as well as traditional sequencers (like ProTools and Cubase). The end result is that these programs have reached a higher level of usefulness, as samples don't necessarily have to be static samples and live songs can directly enter post-production or even be altered in more complex ways than a live DJ program would allow.
And as such, loop-based composition, especially in recent years, has become an easy and attractive way of creating music.