Avoid all the low-frequency pitfalls and learn to achieve the perfect foundation for any mix, with our bass-mixing masterclass...
H ow do I mix bass? It's a simple question, but compare a dozen records picked at random and you'll see that there's no simple answer. When it comes to instruments, 'bass' can mean (at the very least) guitar, upright, drum or synth. Each can perform many musical roles, and every genre has different conventions for low-end sonics. In this article, I'll help you make sense of all that, whatever instruments or genre you're working with. Cancellation Insurance
A bass 'sound' is often a combination of several similar signals: for example, electric bass can be multi-miked; a DI signal may be captured; and you might introduce MIDI-triggered layers to fill things out further. Such shenanigans give you tremendous power to refine your sound, but also enough rope to hang yourself, because the layers don't always reinforce each other when mixed. In fact, they can cancel gruesomely at certain frequencies if there are polarity or phase mismatches — so you need a clear understanding of phase and polarity! There's an in-depth article on the SOS web site (/sos/apr08/articles/phasedemystified.htm) but I'll run through the basics.
Phase differences are caused by one signal being delayed relative to another; and polarity differences are caused by one waveform being inverted relative to another. If you're unlucky, the phase/polarity relationship between a pair of similar signals can result in tonal carnage when they're combined, and you must tackle such issues as early as possible.
With multi-mic/DI recordings, a good way to start is to zoom in on their waveforms and try to match them up as closely as possible, so that phase and polarity differences are minimised and you get the strongest reinforcement. Sort out any obviously polarity-inverted waveform first — by either processing the audio region or hitting that channel's polarity-inversion switch — and drag the audio regions to line up better. If judging things visually is tricky, hunt for transients, which tend to be more easily identifiable.
Now to start refining things by ear. Put the first two tracks out of polarity with each other, fade them up to equal levels, and adjust the timing offset between them to achieve the strongest cancellation. Returning to a matched polarity will then give you the fullest composite sound. Repeat this process, adjusting the timing of each new layer in relation to those you've phase-matched.
It's by no means 'wrong' to deliberately mismatch polarity and phase settings to radically transform what was captured (this is art, after all) but creative phase-cancellation is something of a lottery, and there's a tendency for it to mess with the relative balance of different note pitches, thus introducing musical irregularities. Phase Me Baby, Right Round...
It's often hard to judge the relative polarity and timing offset of mic and DI bass signals by looking at their waveforms, (upper pair). It's easier if you focus on transients, such as the note onset (lower pair). Even then, though, you need to use your ears.