Not a single effect has occupied my time as much as distortion in the three years that I've played bass. Chorus? Set it thick and shiny, then forget about it. Envelope? As long as it quacks, I'm not particular. Slap? Crank the compression and drop the mids. But getting a good fuzz bass has been like Pulling Teeth, pardon the pun.
Even for a traditional bassist, I think distortion is a challenge. Guitarists get all the best high-gain pedals, but those same effects tend to filter out the low frequencies, with the end result that the bass disappears in the mix. Dedicated bass pedals started adding a blend knob to combine dry signal with the overdrive. For some settings, this works--on others, the Blend knob doesn't really blend, and it sounds like two instruments playing simultaneously, or even worse, a horde of bees following a weak bass around.
For players who just want a little growl, the sound is easier to achieve. I hear a lot of good comments from Sansamp Bass DI users, which can create a growling tube amp sound. But I'm not a low-gain player. Even when I played more conventional bass roles, I wanted to be able to fill a huge space of sound. Nowadays, I need a distortion that can be a jack of all trades--good on single lines or chords, giving me a full-bodied low end as well as a sharp high fuzz. I could pretty much get that from the MXR M-80 live, but when recording it was hit or miss. And since I record my loop performances to a single track, I needed it to consistently sound right without a lot of extra EQ.
Moving to the VST effects rig was the perfect chance to be able to create my own distortion from a blend of the many free plugins available, and I spent three nights tweaking it until I could get a good result in the mix of several songs. I'll post a cover of something in a sketchpad as an illustration as soon as possible. Here's how I cooked up an overdrive that doesn't make me cringe.
First of all, I knew that the best bass distortions usually involve at least two different amps blended together. Tim Commerford, who may have the best single-line bass sound in rock, uses three amps with increasing amounts of dirt in each. John Entwhistle, whose bass sound was groundbreaking, split the sound by into separate high and low frequencies, then ran them through a mix of guitar and bass amplifiers. So my first goal was to achieve the same thing through two different plugins, EQ'd to fit together into one big sound. In Phrazor, you do this by using the two busses for each effects track--one receives dry signal, and the other is wired in series, with separate input volumes for each.
For the bass half, I used Audio Damage's Fuzz Plus 2. The Fuzz Plus actually doesn't do a great fuzz in my opinion--it's more of a very heavy drive. That's perfect for a growling low end that'll support but won't stick out too cleanly. I dimed the fuzz control, but cut the tone all the way down (Phrazor tells me it's set at 400Hz). On top of that sound, I ran a second signal chain through the series bus with a Tube Screamer into a Marshall JCM 900 amp emulation, both from the Simulanalog Guitar Suite. The Tube Screamer gives the amp a bit more oomph, just like its real-world counterpart, and the Marshall preamp has its lows removed and its mids severely cut. That gives me a wide high-end fuzz to sharpen and define the lower frequencies.
Balancing those two signals together gave me a full, uniform fuzz, but it was still a bit too digital-sounding. That's happened to me before, like when I tried to crank the overdrive for Sketchpad 6 ("Strange Chemistry") and ended up with harshness and clipping. To tame the harsh high frequencies without blunting the amp's sound, I added a low-pass filter after the amp simulation. A low-pass does exactly that: it lets frequencies below a certain point through, but anything higher is removed. The filter is set at around 9KHz, which is very restricted (most people can hear past 16KHz). Normally, a filter set that far down would make the amp sound muffled as all the treble was removed, but I also raised the resonance, so that frequencies near the cutoff were actually boosted. The harshness was still far enough past the cutoff to be eliminated, and the resonance accentuated particular thicker parts of the fuzz. The end result was a classically scooped high-gain distortion, but one that has lower gain at the bass end for a meatier tone. I could probably still spend weeks or years tweaking it, but it's a solid and reliable foundation for recording.