Inside every bass note…
Play a note from a saw wave oscillator – any note, not just bass – and check out the resulting sound on a frequency analyser. What you see are a series of harmonics, starting at the frequency of the note you’re playing, and continuing at intervals of that frequency. For example, in the image below we’re playing an A2, which is 110Hz. We see a harmonic at 110Hz, then the next at 220Hz (110 x 2), another at 330Hz (110 x 3), 440Hz, 550Hz, 660Hz and so on.
Switch the oscillator to a sine wave, though, and you should only see one of these harmonics – the original 110Hz (if you see more, you may have some distortion in the signal path). We can actually start to recreate the saw wave by playing just sines, adding to the original A2 (110Hz) note with the notes A3 (220Hz), E4 (about 330Hz), A4 (440Hz), C#5 (about 550Hz).
We could keep going, but we’d need a lot of fingers. What we’re trying to get across is that a bass note – as long as it’s been made using a ‘complex’ oscillator (ie, not just a sine wave) – actually contains many harmonics at many frequencies, and these frequencies are musically related to each other.
You can find these harmonics in almost every sound we consider musical: a synth, a string, a trumpet, a clarinet, a vocal and anything else. The ‘times two, times three’ relationship is usually the norm, although some instruments – a xylophone or a bell, maybe – have different relationships between their harmonics. The point we want to get across here, though, is that when you create a bass sound, it contains energy in the lowest frequencies, sure, but there’s also much more happening further up.
Bass and EQ
So while your ‘bass frequencies’ are always low, your ‘bass sound’ might take up a far broader range of frequencies, with the sub bass, bass, low-mids, high-mids and possibly even the highest frequencies playing a role in the sound. That means that it’s helpful to identify which parts of your patch, sample or instrument are giving it the character it has, in order to emphasise or de-emphasise each of them while mixing the bass into a multitrack mix.
In the low-mids (250Hz - 1kHz), boxiness can be a bad quality you’ll want to cut, while boosting might emphasise any warmth already present in the signal. In the high-mids (1 - 4kHz), you might find the ‘nose’ of your bass sound; the area that gives it its bite and helps it attack further up the frequency spectrum. This may be more a hangover from bass guitar mixing techniques, though, and for synthesised bass sounds, it’s possible to give a sound a character of your choosing by adding a little something extra at these high-mid frequencies.
No size fits all
We’re avoiding giving you specific frequencies and recipes for bass here for a reason: your bassline and your whole track will determine which frequencies need care and attention, and why. From synth sounds and timbres to note choices, the number of instruments and the arrangement – nobody can tell you exactly which frequencies to boost, reduce or chop off completely, because different tracks contain energy and character at entirely different places. We’re afraid it’s time for us to pull out the old ‘use your ears’ card here.
Top: A saw wave oscillator playing an A2 note – we can see harmonics at 110Hz, 220Hz, 330Hz, etc. Bottom: The same note on a sine oscillator creates only one spike, at 110Hz