One of the trickiest things about bass tone is nailing a good distorted sound. Unfortunately it’s usually not just a matter of stomping on a distortion pedal and having a usable tone come out of the speaker. The low frequencies that a bass dwells in don’t tend to play very nicely with distortion. So let’s look at one way of getting some serious grindage along with your rumble.
The trick to getting a distorted bass to sound good is usually to run two signals: a clean one and a dirty one. If the low frequencies are too distorted you’ll lose the tightness of your attack and the precision with which you lock in with the kick drum. So it’s a good idea to split your signal into two chains and use each signal for something different. You can do this with two amps if you have them, or with some kind of signal splitter or a pedal with stereo outs then a small mixer to recombine the two sounds. Try using a clean sound for the low frequencies: roll off the high end, dip the mids and do away with the treble to leave behind a big, bassy but clean tone, similar to what a subwoofer might pump out in a home theatre setup. To really maximise the punch, add some compression or limiting with a medium attack time. This signal probably won’t carry much pitch information, but the important thing is to really lay a sonic foundation which performs the rhythmic role of what a bass is designed to do.
For the other signal, try a fuzz or overdrive pedal. If your dirt pedal has comprehensive tone sculpting controls, dial out the low end and focus on the mids and treble (and if it doesn’t, you might need to use an EQ after the fuzz/overdrive). Generally you’ll want to still be a little bit conservative with the treble, because a fizzy bass distortion will clash with the cymbals and mess with the mix. So roll off anything over 5kHz, and don’t be afraid to get some midrange in there because that’s where a lot of the harmonic information of the note lives. You don’t necessarily need to compress this signal. In fact sometimes it’s more effective if it has a little extra dynamic range to it. But if you do compress it, go nuts! Bass overdrive can sound really great when it’s used on Rush-style riffs where the bass is leading the charge.
Having said that, if you’re playing death metal it’s okay to scoop the midrange out of your distorted tone and boost the treble a bit. You might even find that you like the sound of a chorus pedal added after the distortion.
One easy way of getting some great bass distortion happening is to use plugins: go direct into your recording interface or mixing desk (via a DI if you need to, obviously), create two audio tracks, send the signal from the bass to both tracks, and create a suite of plugins for each track: one for the clean, low-end stuff and one for the dirty mids and highs. You can get really creative here and even increase the track count. Try one channel of clean subwoofer-y bass, one of punchy compressed overdrive and one with an envelope filter. Or apply tremolo and stereo ping pong delay to the high sound to create synth-like textures while still holding down the low end.
And when you throw pitch-shifting plugins into the equation, the sky’s the limit. I’ve had good results from using a floor multi effects unit to add two harmonies – one an octave up, the other an octave and a fifth up – then smothering this with distortion and delay to add guitar-like power chords to a track. It’s the kind of thing that might sound a little bit artificial when listened to by itself, but you can get away with it when combined with drums, guitar and vocals in a mix.