Creating Bass Sounds

1. The Oscillator
   For bass sounds, you can use any of the first three wave forms. Using triangle waves will result in deep, sine-like sounds, great for R&B and soul. Sawtooth waves will get you a more solid, defined sound, good for funk, techno and dance sounds as well as for emulating original bass guitar sounds. If you're trying to create an electro-like bass sound, the square wave form is just what you need.
2. The Envelope Generator
   A good start for bass sounds as well as lead sounds is setting the attack, decay and release fairly low, the sustain value quite high and the hold time off, resulting in a 'snappy' envelope. When your sound needs to have a sharper attack, lower the sustain value.
3. The Cut-off Filter
   Using the cut-off filter really is essential when creating bass sounds. To get warm and deep sounds, start with the frequency and peak values around position 5. For techno and dance sounds, turn the peak value up to get those freaky filter effects.
4. Modulation
   One thing that definitely works great with bass sounds, is modulating the cut-off frequency using the envelope generator (the EG knob in the filter section). Slightly modulating it with the modulation generator (the MG knob) works quite well for moody, deep sounds.
5. The Finishing Touch
   Adding a bit of portamento often works great for funky and analog-like sounds. Also adding just a little bit of pink or white noise can give good results in combination with the cut-off filter. It can be very worthwhile to experiment with the filter modulation EG value and with keyboard velocity modulation.

Next: Creating Lead Sounds

See Also
Creating sounds
Using FabFilter One