Synth bass in dubstep was heavily influenced by D’n’B and so adheres to some very similar principles (ie, saw or sine/triangle/square waves stacked together, compressed and EQd, then overdriven using distortion or overdrive/granular plug-ins for a nastier, grittier sound.
The infamous dubstep bass ‘wobble’ can be recreated by stacking a sine and square together, compressing a little, adding some white noise, resonance and distortion/overdrive, then adding an LFO modulating filter cutoff synced to your DAW’s MIDI clock and set to eighth notes.
Also, sending keyboard velocity to filter cutoff works well when playing this kind of bass, as does using band-pass and comb filtering, plus detuning and/or chorus.
Finally, try automating glide/portamento, or recording in pitchbend between notes to smooth transitions and give a more liquid feel.
Dubstep wobble bass
Hear it on: Excision – Subsonic; Skream - Midnight Request Line