PRODUCTION EXPO 2014: Nowadays, the term 'bass' is used somewhat loosely. We're used to hearing the fundamental frequency (or first harmonic) of a bass note over a club PA or subwoofer system, but we actually perceive far more bass if the sound's upper harmonics (ie, midrange frequencies) are also present.
These harmonics are even more vital if we're listening on laptop speakers or smaller-range headphones (which cannot reproduce bass frequencies), as they still provide us with the sonic information that tricks us into thinking we're hearing a huge 'bass' sound.
But what if your bass sound is lacking upper harmonics? Using layering, this extra info can be added, arriving at a bass sound with the best of both worlds. Begin with the fundamental (ie, a pure sine wave) to give the sound power in the lower octaves, then duplicate this sine and distort the copy to generate new upper harmonics.
As with subtractive synthesis, this distorted layer can then be filtered, modulated and widened to provide mid-range movement and texture to the sound whilst your original sub holds it down in terms of solidity and power.
The splitting and/or layering of basses can be taken to even more creative extremes. As most club sound systems are in mono, it's generally a good idea to keep all frequencies below about 300-400Hz in the dead centre of the mix. This splitting lets you create the desired width using spatial effects on your mid/upper-mid layers.
For more videos like this check out Computer Music issue 199.