The SCIENCE of Mixing Perfect Kick & Bass

Phasing Issues in the Low-Frequency Range

Simply put, the low-frequency range is harder to mix because of the physics of sound waves.

Whereas higher frequencies have multiple oscillations within a short distance, low frequencies have incredibly long wavelengths. For example, 40Hz has a wavelength of almost 30ft - which explains why when people put subwoofers in their cars, they still can’t hear the bass as loud as we can from outside the car - they’re too close to the subwoofer for the waveform to fully travel.

But it’s when we combine the physical nature of waveforms with our perception of them that we really run into problems.

People perceive notes as being separate, not by their exact frequency, but by the ratio of their respective frequencies. This ratio is 1.06; in other words, a 6% change in the frequency is needed for us to hear these frequencies as 2 separate notes.

For example, if I play the note A4, which has a frequency of 440Hz. - and we multiply that by 1.06, we get 466. Guess what the frequency of A#4 is? Yep - 466Hz.

But what does this have to do with the lows?

Well, let’s look at the note E1, which has a frequency of 41.2Hz. Multiplied by 1.06, the next note we can perceive is 43.6Hz. So, in the low mids or with A4, we have 26Hz in between the perceived notes, but here we have only 2.4Hz between the 2.

Although we can hear these as separate notes, physics really doesn’t like having these 2 notes present at the same time.

Playing both results in significant destructive interference, in which the 2 waveforms periodically overlap in a way that causes complete phase cancellation.

If you’ve ever heard of binaural beats, this is how they’re made - listen, and you’ll notice this beating sound that occurs at a constant rate.

Watch the video to learn more >

How Can We Use this Info?

The first way we can improve our mixes actually comes from composition.

Say I have a kick drum, and its fundamental is E1. Then, the bass hits an F1 note at the same time as the kick. We’re guaranteed to have phase cancellation in the lows, making mixing incredibly difficult.

But, what if the kick hits E1, and the bass plays F2 instead? Already we’ve greatly improved the low end by reducing phase cancellation.

Building on this idea - let’s say the kick drum has an overtone, and it’s F#2. This means we have E1, F2, and F#2 playing at the same time - F#2 will likely interfere with F2, which, again, is the bass’s fundamental.

I definitely don’t want the bass’s fundamental to have periodic phase cancellation - so we could attenuate this overtone on the kick with EQ.

And this brings me to my next point, which is We Can Combine Processing with Composition

Processing and the music being processed are inherently linked - and with particular processors, we can shape the relationship between notes and instruments to our advantage - which we already saw with EQ.

So, same example, the kick’s fundamental is E1 and it has an overtone of F#2 - which we’ve attenuated with EQ.

But, what if we could change the kick’s harmonics? Well, that’s why we have saturators - they generate harmonics or multiples of the fundamental frequency.

So now, instead of a kick that has an overtone at F#2, I can generate a harmonic at E3. Not only does this E3 note interfere with the bass’s fundamental less than F#2, but it also sounds more musical since it’s directly related to the kick’s fundamental.

Here, take a listen and notice how the 2 instruments are more distinct.

Watch the video to learn more >

High Frequencies of Kick and Bass

We don’t think about kick and bass as having high frequencies - but at the very least, they have a significant presence in the mids and often the high mids.

Again, we can use this to our advantage when mixing them.

As we discussed, the gap between frequency ranges in the mids and high mids is much larger than in the lows - this means if we accentuate and amplify the high frequencies of the kick and bass, they’ll become much more distinct due to significantly less phase cancellation in these ranges.

This is why I recommend using exciters on the kick and the bass - it adds harmonics just like a saturator but measures the fundamental as being higher in frequency. This means the harmonics it introduces are also higher in frequency.

Subsequently, we amplify the high ranges of the kick and bass, causing increased distinction between the instruments and, again, a lower ratio of phase cancellation to the relevant signal.

Not only can we introduce high-order harmonics with exciters, but we can also emphasize the harmonics and overtones that are already present with transient expanders. The majority of high frequencies in a kick and a bass occur within the first roughly 50ms of it being hit or plucked or during the signal’s Attack and Decay.

By introducing a mild transient expander, we amplify these frequencies, again increasing the distinction between these 2 instruments.

Watch the video to learn more >

If you combine the ideas here and monitor the relationship between your kick and bass, or whichever low-frequency instruments you have, you’ll find the lows to be a much easier range to mix.