The most important instrument in electronic dance music -- if a genre of music isn't (at least partially) defined by having a 303, then it's partially defined by not having it. Analogous to the piano in classical music, I suppose. This instrument's popularity is due to its distinct, unmistakable sound, which can go from crystal clear to violently harsh, or from deeply abstract to easily danceable. The distinctive sound comes from a few of its characteristics that just aren't shared by many other synths, except the ones made just to emulate a TB-303.

  1. The filter used in the TB-303 is 3 pole, instead of the regular 2 or 4, which means that its sound reduction rate is 18 Db per octave, instead of 12 or 24. It is also made with a modified diode ladder, using transistors wired to work like diodes. Most synthesizers use a pure capacitor and resistor setup for filtering. The filter can only be pushed into self-resonance in the upper octaves, and when it is it produces a lot of harmonics that give sort of a biting shriek to the machine's sound.

  2. The sequencer is a truly interesting beast. Programming a pattern is accomplished in three passes: adding the notes to be played, adding the length of the notes (which can be done in two equally unintuitive ways :-), and adding accent and slide to the notes. There are manuals available on the internet that explain how to do this, but rest assured it is not an easy task to turn a given piece of sheet music into a 303 pattern. Some artists don't even try to work out a pattern before they put it in, they just push buttons to get semi-random patterns, and keep the ones that sound good.

    The accent function of the sequencer increases the filter resonance amount and the volume of the note. With the resonance turned way up, this makes the note sound completely different. Also, when the volume -- controlled by a VCA -- is changed in this manner, the filter cutoff bounces up and down a little bit, adding even more strangeness to the accented note's sound.

    Another secret weapon of the sequencer is its slide function. Instead of sliding at a variable rate -- so you end up on closer notes faster, like on most synths -- it slides at a constant rate (about 60 ms) no matter how far away a note is. A common acid techno trick is to play most of the pattern in a low octave, but have one or two notes slide to notes a few octaves up, producing an attention-grabbing sort of vvweeeep sound. Also, where most portamento is done during the first little bit of the next note, the 303 sequencer recognizes a slide will be coming, and starts the slide at the end of the preceding note. If the 303 is playing lots of short notes at a high tempo, the slide will be unable to reach the next note in the allotted 60 ms, which sounds like a terrifically random chopping noise in the pattern.

  3. The oscillator is pretty unremarkable, except that it can be changed between a square and sawtooth wave with a switch on the back of the machine. The sawtooth wave is by far the more "acidic" sounding one, and is used extensively by the acid techno scene (Chris Liberator, Rowland the Bastard, DDR, etc.). Without much filtering, it sounds vaguely like a trumpet. The square wave is much cleaner and beepier sounding, but can get pretty distorted with the filter. It is used by ambient artists, as well as on Plastikman's more abstract material, and sounds something like a clarinet when not modified. Every once in a while, a techno track will let the 303 get quiet, then switch from one waveform to the other and bring the pattern back in, adding a nice dramatic change to the music.